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Huanhuan Zhang, Jialing Ou, Guoying Zhao, Jingshan Hou, Yufeng Liu, Xin Qiao, Zhongzhi Wang, [Ji-Guang Li](https://orcid.org/0000-0002-5625-7361), Yongzheng Fang

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[Preparation and luminescent performances of tellurite glass coated CsPbBr3@glass film for remote LED color converter](https://mdr.nims.go.jp/datasets/66e39db4-4fcb-4d2b-bfa9-57977e752c9b)

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1  Preparation and Luminescent Performances of Tellurite Glass Coated CsPbBr3@glass Film for Remote LED Color Converter Huanhuan Zhang1, Jialing Ou1, Guoying Zhao1*, Jingshan Hou1, Yufeng Liu1, Xin Qiao2, Zhongzhi Wang2, Ji-Guang Li3, Yongzheng Fang1* 1 School of Materials Science and Engineering, Shanghai Institute of Technology, Shanghai 201418, PR China 2Baotou Research Institute of Rare Earths, Baotou, 014030, China 3Research Center for Functional Materials, National Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan *Corresponding author, E-mail addresses: zhaogy135@126.com; fyz1003@sina.com. ABSTRACT: We know that perovskite quantum dot (PQD) glass is one of the effective ways to achieve high stability, high reliability and high weather resistance. However, quantum dot glass is still unable to achieve completely uniform crystallization as a whole, so quantum dot glass has to be used in the form of powder by mixing glue. The use of organic matter leads to the problems of heat accumulation and stability. In this work, the concept of double cladding encapsulation was realized to solve the above problems in the application of quantum dot glass, and the remote inorganic fluorescent film is prepared. CsPbBr3 PQDs embedded in borosilicate glass (PQDs@glass) were prepared using traditional melting-quenching and heat-treatment processes. By optimizing the raw material composition and melting conditions, excellent PQDs@glass were obtained, and its photoluminescence quantum yield (PLQY) was as high as 88.06%. The CsPbBr3 PQDs embedded borosilicate glass has been dispersed in tellurite glass film again along with color-compensatory red-emitting nitride phosphor, which is a doubly encapsulated system with inorganic glass matrixes to improve stability and color-tunability. A series of prototypes light-emitting diode devices were assembled based on the as-made doubly encapsulated glass film with a commercial blue chip, resulting in bright white light luminescence at a color temperature of 3920 K and a high color rendering index of 87.2. Keywords: Remote glass film; CsPbBr3 perovskite quantum dot; High quantum yield; Double REVISED Manuscript (text UNmarked) Click here to view linked Referenceshttps://www.editorialmanager.com/lumin/viewRCResults.aspx?pdf=1&docID=17531&rev=3&fileID=312898&msid=9aeb65cd-c758-4604-b03b-706ea58c704bhttps://www.editorialmanager.com/lumin/viewRCResults.aspx?pdf=1&docID=17531&rev=3&fileID=312898&msid=9aeb65cd-c758-4604-b03b-706ea58c704b 2  Encapsulation 1. Introduction   Recently, due to the unique optical properties, inorganic cesium lead halide (CsPbX3, X = Cl, Br, I) perovskite quantum dots (PQDs) have attracted growing attention[1-4]. The photoluminescence (PL) of lead halide perovskite PQDs covers the entire visible spectral region with high quantum yield, which may find potential applications in various photoelectronic devices[5-8]. Thermal corrosion of monodisperse perovskite CsPbBr3 nanostructures in amorphous glass substrates and during co-sintering with low melting point glass is negligible, ensuring good luminous properties. By the passivation of surface traps in wet-chemical synthesis strategy, the photoluminescence quantum yields (PLQYs) of CsPbBr3 can reach over 90% in green spectral region[9]. However, the PLQYs of glass-stabilized CsPbBr3 is relatively lower than the colloidal counterpart, and the highest value of PLQY is 81% that is obtained from boron-germanium glass, which hampers their practical application for  photoelectronic devices[10]. In general, borosilicate glass is characterized by excellent physical and chemical stability compared to other glass systems when exposed to air or moisture. Owning to the ligand sensibility of CsPbBr3 PQDs in glass, it is necessary to optimize the borosilicate glass grid structure to achieve high PLQY and long-term stability. As is known to all, the present commercial w-LED is assembled with yellow yttrium aluminum garnet phosphor and packaging material-organic epoxy silicone mixed, using "dispensing" technology means coated on LED chip[11-14]. However, as the LED power increases, the operating time increases, resulting in the PN junction temperature rise, at this time the chip temperature can be as high as 150~200 °C, which will make the phosphor temperature quenching effect[15,16]. It will also make LED device efficiency decline, color coordinate deviation, service life suddenly reduced service life of a sudden reduction[17,18]. It has been proposed to replace organic materials such as phosphorus in glass (PiG) with inorganic components. The PiG method is a simple mixture of transparent glass and phosphor sintered together at a certain temperature. Yoon et al. suggested a novel inorganic color converter for white LED with a single phosphor-in-glass (PiG) plate. CsPbBr3 perovskite nanocrystals embedded in germanate glass was used as a green phosphor and mixed with a transparent silicate glass to prepare the PiG plate. The photo stability and thermal stability of CsPbBr3 perovskite nanocrystals are improve[19]. Compared to glass ceramic plate, PiG film can be  3  easily sintered and its color coordination can be simply controlled by adjusting the rations of PQDs@glass and phosphors. In addition, PiG film has high thermal conductivity and adjustable high refractive index, which can diffuse the heat accumulated on the phosphorus layer onto the silicon glass substrate. Therefore, the PiG film exhibits the robust stability when compared with the organic encapsulants. Red nitride phosphors have been widely studied for their excellent photoluminescent behaviors. Unfortunately, the commercial red nitride phosphors suffer from the poor structural stability during the low temperature co-sintering procedure[20]. Therefore, the mother glass protecting the embedded phosphor particles is a key factor identifying the photoluminescent performances of PiG.  Tellurite glass is characterized by TeO2 as the main component, often by adding some oxides and halides to improve the glass forming ability and stability[21]. As a kind of heavy metal oxide glasses, tellurite glass has its own unique advantages including: high refractive index (around 2.0), wide infrared transmission range (0.35-5 um), low phonon energy in oxide glass (about 600-850 cm-1) and low melting temperature (800-950 °C)[22]. Benefiting from the high refractive index and low phonon energy, high absorption and emission cross section and low non-radiative transition rates of rare earth ion can be obtained[23,24]. As to the use of mother glass for PiG, the high refractive index of tellurite glass is favorable to matching the refractive index of doped phosphor to a greater extent[25]. Besides, the relatively low glass transition temperature will reduce the thermal corrosion of photoluminescent phase. Therefore, tellurite glass is considered to be an excellent candidate for PiG.  In this study, the concept of double cladding encapsulation was realized in borosilicate stabilized CsPbBr3 PQDs using tellurite glass as the outer clad. Firstly, we obtain the CsPbBr3 PQDs with the high quantum efficiency through the regulation of glass grid.  By spinning coating technology, the as-made borosilicate stabilized CsPbBr3 PQDs and commercial nitride phosphors are uniformly dispersed in tellurite glass on the silica substrate. Finally, after determining the optimal sintering temperature, we prepared a series of QiG(quantum dots in glass)@glass flakes and then mounted them on a blue chip with a wavelength of 450 nm to produce white light. The effects of sintering temperature and glass-phosphor ratio on the properties of QiG@glass were discussed.  2. Experimental section  4  2.1 Fabrication of CsPbBr3 PQDs in borosilicate glasses The glass carrier is prepared from high-purity SiO2, H3BO3 and ZnO powders, and the perovskite components were added into Cs2CO3, PbBr2 and KBr (CPB). The purity and supplier of all reagents are given in Table 2. All experiments are conducted without toxic and harmful organic reagents. All raw materials are first ground into a powder in an agate mortar and then transferred to a corundum crucible. The powder is melted in a muffle furnace at 1200 °C for 15 min. The molten glass is then poured into a preheated copper mold and immediately transferred to a muffle furnace at 350 °C and held for 2 h to release stress. Finally, the precursor glass was heat treated near the glass transition temperature to obtain CsPbBr3 PQDs multi-component glass. Stored at a heat treatment temperature of 470 °C for 10 hours, a series of CsPbBr3 PQDs multi-component glass samples were obtained. For further study, the resulting glass is ground into a powder or optically polished. Table 1. Glass compositions [xSiO2- (67-x) B2O3-16ZnO (x=35, 38, 41, 48, 58 mol%)] and the added perovskite-related components. Sample SiO2 B2O3 ZnO Cs2CO3 PbBr2 KBr 35Si 35 32 16 9 3 6 38Si 38 29 16 9 3 6 41Si 41 26 16 9 3 6 48Si 48 19 16 9 3 6 58Si 58 9 16 9 3 6 8CPB 38 29 16 8 2 4 9CPB 38 29 16 9 3 6 10CPB 38 29 16 10 4 8 11CPB 38 29 16 11 5 10 12CPB 38 29 16 12 6 12 9CPB-1.8 38 29 16 9 5.4 10.8 9CPB-2.1 38 29 16 9 6.3 12.6 9CPB-2.4 38 29 16 9 7.2 14.4 9CPB-2.7 38 29 16 9 8.1 16.2 9CPB-3.0 38 29 16 9 9 18 2.2 Fabrication of QiG@glass films Glasses with composition 20B2O3-60TeO2-10ZnO-10Na2O were prepared by using analytical grade B2O3, TeO2, ZnO, Na2CO3 as starting materials. Based on a certain stoichiometric ratio, the starting materials were weighted and mixed together. It was thoroughly ground and placed in an  5  alumina crucible and then melted for 0.5 h at 950 °C in a muffle furnace. Subsequently, the melt were poured into a preheated brass mold and annealed at 300 °C for 15 h. Glass samples were cut and carefully polished to meet optical measurements. Each sample looks more transparent. The slurries were mixed by suitable powder dosing: the prepared glass-stabilized CsPbBr3 PQDs powder, Sr2Si5N8 red phosphor, and tellurite glass matrix. All powders were mixed into organic vehicle which composition were terpilenol and ethyl cellulose at 80 K for 12 h by 700 rpm. The mixed slurry is spin coated onto the glass substrate (r = 20 mm) by scraping and then the resultant samples were dried at 150 °C for 5 h in order to make the organic matter completely volatile. Finally, QiG@glass film was obtained by sintering the glass film at 460 °C for 30 min.  Table 2. Purity and supplier of each starting reagent. Start reagent Purity Supplier SiO2 GR Shanghai Maclin Biochemical Technology Co., LTD H3BO3 GR Shanghai Titan Technology Co., LTD ZnO AR, 99.0% Shanghai Titan Technology Co., LTD Cs2CO3 99.9% Shanghai Merrier Chemical Technology Co., LTD KBr AR, 99.0% Sinopharm Chemical Reagent Co. LTD PbBr2 99 % Shanghai Titan Technology Co., LTD TeO2 99.99% Chengdu Zhongjian Materials Optoelectronic Materials Co., LTD Na2CO3 AR, ≥ 99.8% Shanghai Titan Technology Co., LTD 2.3 Characterization The phase purity of phosphor powders and QiG@glass firms was confirmed by using an X-ray powder diffractometer (TD-3500, Dandong, China) with Cu Kα irradiation at 40 kV and 40 mA. The microstructure and elemental mappings were observed by a field-emission scanning microscope (SU70, Hitachi) equipped with an energy-dispersive X-ray spectroscope (EDS) system and Transmission Electron Microscopy (FEI Tecnai F20). The photo-luminescence (PL) and photo-luminescence excitation (PLE) of the samples were measured using a spectrometer (Hitachi F-7000) with a xenon discharge lamp. FS5 fluorescence spectrometer is standard equipped with absorption detector, which can achieve fluorescence and UV testing functions on the same instrument at the same time, so we tested the quantum yield by FS5. Decimal methods can also be applied to a wider javascript:; 6  range of sample types and are the only reliable method for samples such as solid powder and thin films. The test requires an integrating sphere that is coupled to the fluorescence spectrometer as a test attachment. In absolute quantum yield testing, all light emitted by a sample is captured using an integrating sphere, and the quantum yield is determined by comparing the number of photons emitted to the number of photons absorbed. Such as formula (1): 𝜂 =𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑝ℎ𝑜𝑡𝑜𝑛𝑠 𝑒𝑚𝑖𝑡𝑡𝑒𝑑𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑝ℎ𝑜𝑡𝑜𝑛𝑠 𝑎𝑏𝑠𝑜𝑟𝑏𝑒𝑑                                               (1) The difference in integral area between the sample and the reference indicates the number of the absorbed photons. The emitted photons were determined by integrating the related emission band. Test the blank curve with the blank sample that comes with the integrating sphere. The scattering curve and the sample curve are combined to calculate the quantum yield. The optical properties of the w-LED module are obtained in the integrating sphere, including chromaticity color coordinates, correlated color temperature (CCT), color rendering index (CRI), luminous efficiency, and electroluminescence (EL) emission spectroscopy (HAAS-2000).  3. Results and Discussion 3.1   Microstructure and luminescence of PQDs@glass  Fig. 1 (a-c) Photoluminescence spectra and PLQY of xSiO2- (67-x) B2O3-16ZnO (x=35, 38, 41, 48, 58 mol%) glass with different CPB components excited at 365 nm.  Fig. 1 shows the photoluminescence (PL) spectra and PLQYs of CsPbBr3 PQDs from borosilicate samples under excitation at 365 nm and 450 nm. It can be seen that the well crystallized CsPbBr3 PQDs formed in B39Si28 glass containing 9CPB-2.4 has the highest PLQY value (88.06%). With the decrease of B/Si ratio, the emission intensity increases first and then decreases, reaching the maximum value at Si38B29, and the change of quantum yield also presents the similar trend. The photoluminescence of sample exhibits the narrow-band emission characteristics of a) b) c)  7  quantum dot materials. It can be seen from Fig. 1(a) that the luminescence of CsPbBr3 PQDs doped glass is controlled by changing the topological structure of the glass. The glass grid structure has an important impact on the precipitation and growth of quantum dots from mother glass, which in turn affects the luminescence performance. Based on our previous work, there exists an optimal B/Si molar ratio that possesses the moderate glass rigidity, which can boost the precipitation of CPB elements and accelerate the growth of nanocrystals from glass network[26]. Therefore, Si38B29 sample is selected as glass host to optimize CPB concentration (PL spectra shown in Fig. 1(b and c))[27]. In order to compensate for the volatile loss of Br element during the melting procedure, excess amounts of halogen compounds, PbBr2 and KBr, needed to be added to the raw material. With the increase of doped concentration, more and more quantum dots polymerize and grow in glass, resulting in an increase in PQDs concentration, it is worth noting that a moderate excess of Br supplementation in raw materials is more conducive to the growth of PQD in glass. The results show that the quantum efficiency of the sample reaches the maximum when the CPB concentration is further increased to 9Cs2CO3−7.2PbBr2−14.4KBr mol%.   As showed in TEM image (shown in Fig. 2(a)), the CsPbBr3 PQDs are evenly dispersed in the glass matrix, and their average particle size is 2.98 nm. High-resolution TEM (HRTEM) image (Fig. 2(b)) evidences homogeneous precipitation of CsPbBr3 PQDs with well-resolved lattice fringes with high-crystallinity, which shows clear lattice fringes with an interplanar distance of 0.288 nm. The lattice fringes have 0.288 nm interplanar distance that corresponds to the [200] lattice plane of the cubic CsPbBr3[28,29]. It can be seen that the PQDs in the glass are different from the cubic form of the colloidal PQDs prepared by wet chemistry, and the PQDs in the glass is a spherical form, which may be due to the restriction effect of inorganic oxidized glass on the growth of PQDs. Elemental mapping of these nanocrystals suggested that these nanocrystals were highly rich in Cs, Pb and Br. In general, the precipitation of CsPbBr3 nanocrystals in the sample was confirmed.   8   Fig. 2 (a and b) TEM image of the CsPbBr3 PQDs@glass. (c) HRTEM micrograph of the CsPbBr3 PQDs@glass. (d-i) B, Si, Cs, Pb, and Br elemental mappings. 3.2.  Microstructure and luminescence of QiG@glass film. QiG@glass films have high thermal stability compared to conventional organic encapsulation; Good moisture resistance; It has the characteristics of corrosion resistance and high chemical stability. The XRD patterns of quantum dot glass, red phosphor and QiG@glass samples are shown in Fig. 3(a). The different peaks correspond to the Sr2Si5N8 and PQDs, which is in accord with that of the pure Sr2Si5N8 phosphor and standard card of CsPbBr3 (PDF #75–0412), respectively. The QiG@glass film has little effect on the phosphors, and the fluorescent crystal phase is intact in glass matrix. Furthermore, the 9CPB-2.4 QiG@glass film was chosen to check the possible reaction between as-prepared glass and the phosphor, SEM, EDS and EDS mapping were carried out. Fig. 3(b-h) indicates that the glass and phosphor powder are uniformly distributed in the tellurite glass matrix. The moderate concentration of pores in film is beneficial to reducing the reflection of incident light to improve the utility of pump light [30,31]. The cross section image (shown in Fig. 3(c)) suggests the phosphor layer with a thickness of approximately 24.54μm has been well adhered on the surface of silica glass substrate after sintering.  1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.005101520  CountGrain diameter(nm)a) b) d) e) f) g) h) i) c)  9   Fig. 3 (a) The XRD patterns of quantum dot glass, red phosphor and QiG@glass samples. (b and c) SEM of QiG@glass film. (d) EDS spectrum of QiG@glass film. (e-h) Mapping image of Te, N and Cs.  We prepared a series of W-LEDs by changing the ratio of quantum dot glass powder to red phosphor. To research the luminescence properties, the prepared QiG@glass film is assembled on the top of the blue chip under the 450 nm irradiation with a drive current of 10 mA (Fig. 4 (b)). To produce white light, we mixed the red phosphor Sr2Si5N8 with glass powder at the content sub-point and then embedded in the tellurite glass to form a QiG@glass. The weight ratio of glass to phosphorus is adjusted from 10:1 to 14:1. The resulting electroluminescence diagram and color coordinates are shown in Fig. 4(a and c). According to EL spectrum and chromaticity diagram, the ratio of glass to phosphor is 13:1, which is the best ratio to produce white light. As the proportion of glass powder in QiG@glass increased, the 450 nm blue component in the spectrum increased, and the light color changed from warm white to cold white, as shown in Fig. 4(c).  f ) g) b) c) e) d) a) h)  10   Fig. 4 (a) Optimum ratio electroluminescence diagram. (b) Schematic diagram of LED package. (c) Color coordinates at different scales and real pictures. Fig. 5(a) shows the excitation and emission spectra of the glass powder and phosphor used in the experiment, respectively. It can be seen that the emission peak of the glass powder is located at 526 nm. It indicates that the emission spectrum of the glass powder and the excitation spectrum of the red powder have a large area of spectral overlap. The emission spectrum of glass powder can theoretically be reabsorbed by red powder and converted into red emission spectrum, which improves the emission intensity of red light, and correspondingly reduces the probability of green light transmitted out of the film to the space. QiG@glass films (the ratio of glass to red phosphor power was 13:1) were prepared at a sintering temperature of 460 °C to 490 °C. As the sintering temperature increased, the color of the sample gradually darkened, and the color rendering index decreased from 87.2 to 55.7. The color temperature increased from 3920 K to 12821 K. The results show that the sintering conditions of the QiG@glass film have a significant effect on the performance of the red phosphor. This may be due to the instability of the crystal phase structure of nitride in glass[32-37]. At a low sintering temperature of 460 °C, the thermal damage can be reduced for better luminous performance. At this temperature, warm white light with high visibility can be obtained.  tellurite glass red phosphor CsPbBr3 glass Blue LED mount 10：1 11：1 13：1 14：1 12：1 b) a) c)  11   Fig. 5 (a) Emission spectrum of glass powder and excitation spectrum of phosphor powder. (b) The electroluminescence diagram of QiG@glass at different sintering temperatures. 3.3 The stability of QiG@glass film The stability of QiG@glass is an important parameter for its applications. The PL temperature dependence was investigated (Fig. 6(a)), showing the PL spectra of QiG@glass at eight typical temperatures of 25, 50, 75, 100, 125, 150, 175 and 200 °C (298-473 K). With increasing of temperature (solid lines), the PL intensity decreased and its peak wavelength was blue-shifted. When the sample were cooled (dashed lines), the PL intensity and the shifted peak wavelength were reversibly recovered. These characteristic temperature dependent PL intensity change and emission peak shift have been commonly found in CsPbBr3 perovskite nanocrystals, which can be attributed to the thermal expansion and phonon−electron interaction[19]. Furthermore, the long-term stability for the QiG@glass samples was investigated by dipping them in water. PL spectra shows that there is no obvious change of PL intensity (Fig. 6(c)) in water for 60 days. Under the protection of tellurite glass and borosilicate glass, the emission intensity is basically unchanged after 60 days of immersion in water. This result confirms that tellurite glass carriers and borosilicate glass are indeed effective in protecting PQDs from decomposition.  a) b)  12   Fig. 6 (a) Temperature-dependent PL spectra (λex = 450 nm) for the QiG@glass in the temperature range of 298-473 K. (b) Integral photoluminescence intensities of QiG@glass specimens recorded during thermal cycling experiment. (c) PL spectra for QiG@glass directly immersing in water for 60 days and inset is a photo of glass in water under the illumination of a blue light chip. (d) Integrated photoluminescence intensities in water stability.  The QIG@glass film was irradiated with a blue light of 300 mA forward current for 0, 3, 9, 21, 45, 93 h, equally its luminescence spectrum was tested (Fig. 7(a and b)), and the luminous intensity only decreased by about 3%. By introducing oxygen into the tube furnace, the oxygen stability of the film was studied by making the film stand in the oxygen environment for 0, 12, 48, 96 h. The luminescence spectrum shows (Fig. 7(c and d)) with no significant change in luminous intensity. Therefore, tellurite glass matrix can protect the stability of PQDs and phosphors effectively.   0       30      60 a) b) c) d)  13   Fig. 7 (a) PL spectra (λex = 450 nm) of QiG@glass under different duration blue light irradiation (b) Integrated photoluminescence intensities in light stability. (c) PL spectra (λex = 450 nm) of QiG@glass under different duration oxygen conditions. (d) Integrated photoluminescence intensities in oxygen stability. 4. Conclusions We successfully deposited CsPbBr3 PQDs into borosilicate glass by melt quenching technique and heat treatment. The quantum efficiency PLQY of CsPbBr3 reached 88.06% after the regulation of various components in the glass. QiG@glass film was prepared by scraping and coating technique. Tellurite glass with low melting point was double coated to protect the stability of phosphors. A red phosphor emitting a wide spectrum was used to improve the color rendering index. The color rendering index of single-luminescent center QiG@glass thin-film conversion W-LED device is up to 87.2, the corresponding color temperature is 3920K, and the color gamut of 111.92% of the NTSC standard.  Acknowledgement Guoying Zhao acknowledges financial supported by Science and Technology Talents a) b) d) c)  14  Development Fund for Young Middle-aged Teachers Fund, Collaborative Innovation Fund (No. XTCX2022-03) of Shanghai Institute of Technology and Development of key technologies for the preparation and application of high-performance rare earth fluorescent block materials (No. BFXT-2022-D0046). Jingshan Hou acknowledges financial supported by the National Natural Science Foundation of China (No. 51902203). Yongzheng Fang acknowledges financial supported by the National Natural Science Foundation of China (No. 51472162). References  [1] Cai C, Wang X, Ling L, et al. 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Journal of Materials Science-Materials in Electronics, 2018, 29(5): 4011-4019.   1  Preparation and Luminescent Performances of Tellurite 1 Glass Coated CsPbBr3@glass Film for Remote LED Color 2 Converter 3 Huanhuan Zhang1, Jialing Ou1, Guoying Zhao1*, Jingshan Hou1, Yufeng Liu1, Xin Qiao2, Zhongzhi 4 Wang2, Ji-Guang Li3, Yongzheng Fang1* 5 1 School of Materials Science and Engineering, Shanghai Institute of Technology, Shanghai 201418, 6 PR China 7 2Baotou Research Institute of Rare Earths, Baotou, 014030, China 8 3Research Center for Functional Materials, National Institute for Materials Science, Tsukuba, 9 Ibaraki 305-0044, Japan 10 *Corresponding author, E-mail addresses: zhaogy135@126.com; fyz1003@sina.com. 11 ABSTRACT: We know that perovskite quantum dot (PQD) glass is one of the effective ways to 12 achieve high stability, high reliability and high weather resistance. However, quantum dot glass is 13 still unable to achieve completely uniform crystallization as a whole, so quantum dot glass has to 14 be used in the form of powder by mixing glue. The use of organic matter leads to the problems of 15 heat accumulation and stability. In this work, the concept of double cladding encapsulation was 16 realized to solve the above problems in the application of quantum dot glass, and the remote 17 inorganic fluorescent film is prepared. CsPbBr3 PQDs embedded in borosilicate glass (PQDs@glass) 18 were prepared using traditional melting-quenching and heat-treatment processes. By optimizing the 19 raw material composition and melting conditions, excellent PQDs@glass were obtained, and its 20 photoluminescence quantum yield (PLQY) was as high as 88.06%. The CsPbBr3 PQDs embedded 21 borosilicate glass has been dispersed in tellurite glass film again along with color-compensatory 22 red-emitting nitride phosphor, which is a doubly encapsulated system with inorganic glass matrixes 23 to improve stability and color-tunability. A series of prototypes light-emitting diode devices were 24 assembled based on the as-made doubly encapsulated glass film with a commercial blue chip, 25 resulting in bright white light luminescence at a color temperature of 3920 K and a high color 26 rendering index of 87.2. 27 Keywords: Remote glass film; CsPbBr3 perovskite quantum dot; High quantum yield; Double 28 Revised Manuscript with Changes Marked 2  Encapsulation 1 1. Introduction   2 Recently, due to the unique optical properties, inorganic cesium lead halide (CsPbX3, X = Cl, 3 Br, I) perovskite quantum dots (PQDs) have attracted growing attention[1-4]. The photoluminescence 4 (PL) of lead halide perovskite PQDs covers the entire visible spectral region with high quantum 5 yield, which may find potential applications in various photoelectronic devices[5-8]. Thermal 6 corrosion of monodisperse perovskite CsPbBr3 nanostructures in amorphous glass substrates and 7 during co-sintering with low melting point glass is negligible, ensuring good luminous properties. 8 By the passivation of surface traps in wet-chemical synthesis strategy, the photoluminescence 9 quantum yields (PLQYs) of CsPbBr3 can reach over 90% in green spectral region[9]. However, the 10 PLQYs of glass-stabilized CsPbBr3 is relatively lower than the colloidal counterpart, and the highest 11 value of PLQY is 81% that is obtained from boron-germanium glass, which hampers their practical 12 application for  photoelectronic devices[10]. In general, borosilicate glass is characterized by 13 excellent physical and chemical stability compared to other glass systems when exposed to air or 14 moisture. Owning to the ligand sensibility of CsPbBr3 PQDs in glass, it is necessary to optimize the 15 borosilicate glass grid structure to achieve high PLQY and long-term stability. 16 As is known to all, the present commercial w-LED is assembled with yellow yttrium aluminum 17 garnet phosphor and packaging material-organic epoxy silicone mixed, using "dispensing" 18 technology means coated on LED chip[11-14]. However, as the LED power increases, the operating 19 time increases, resulting in the PN junction temperature rise, at this time the chip temperature can 20 be as high as 150~200 °C, which will make the phosphor temperature quenching effect[15,16]. It will 21 also make LED device efficiency decline, color coordinate deviation, service life suddenly reduced 22 service life of a sudden reduction[17,18]. It has been proposed to replace organic materials such as 23 phosphorus in glass (PiG) with inorganic components. The PiG method is a simple mixture of 24 transparent glass and phosphor sintered together at a certain temperature. Yoon et al. suggested a 25 novel inorganic color converter for white LED with a single phosphor-in-glass (PiG) plate. CsPbBr3 26 perovskite nanocrystals embedded in germanate glass was used as a green phosphor and mixed with 27 a transparent silicate glass to prepare the PiG plate. The photo stability and thermal stability of 28 CsPbBr3 perovskite nanocrystals are improve[19]. Compared to glass ceramic plate, PiG film can be 29  3  easily sintered and its color coordination can be simply controlled by adjusting the rations of 1 PQDs@glass and phosphors. In addition, PiG film has high thermal conductivity and adjustable 2 high refractive index, which can diffuse the heat accumulated on the phosphorus layer onto the 3 silicon glass substrate. Therefore, the PiG film exhibits the robust stability when compared with the 4 organic encapsulants. Red nitride phosphors have been widely studied for their excellent 5 photoluminescent behaviors. Unfortunately, the commercial red nitride phosphors suffer from the 6 poor structural stability during the low temperature co-sintering procedure[20]. Therefore, the mother 7 glass protecting the embedded phosphor particles is a key factor identifying the photoluminescent 8 performances of PiG.  9 Tellurite glass is characterized by TeO2 as the main component, often by adding some oxides 10 and halides to improve the glass forming ability and stability[21]. As a kind of heavy metal oxide 11 glasses, tellurite glass has its own unique advantages including: high refractive index (around 2.0), 12 wide infrared transmission range (0.35-5 um), low phonon energy in oxide glass (about 600-850 13 cm-1) and low melting temperature (800-950 °C)[22]. Benefiting from the high refractive index and 14 low phonon energy, high absorption and emission cross section and low non-radiative transition 15 rates of rare earth ion can be obtained[23,24]. As to the use of mother glass for PiG, the high refractive 16 index of tellurite glass is favorable to matching the refractive index of doped phosphor to a greater 17 extent[25]. Besides, the relatively low glass transition temperature will reduce the thermal corrosion 18 of photoluminescent phase. Therefore, tellurite glass is considered to be an excellent candidate for 19 PiG.  20 In this study, the concept of double cladding encapsulation was realized in borosilicate 21 stabilized CsPbBr3 PQDs using tellurite glass as the outer clad. Firstly, we obtain the CsPbBr3 PQDs 22 with the high quantum efficiency through the regulation of glass grid.  By spinning coating 23 technology, the as-made borosilicate stabilized CsPbBr3 PQDs and commercial nitride phosphors 24 are uniformly dispersed in tellurite glass on the silica substrate. Finally, after determining the 25 optimal sintering temperature, we prepared a series of QiG(quantum dots in glass)@glass flakes and 26 then mounted them on a blue chip with a wavelength of 450 nm to produce white light. The effects 27 of sintering temperature and glass-phosphor ratio on the properties of QiG@glass were discussed.  28 2. Experimental section 29  4  2.1 Fabrication of CsPbBr3 PQDs in borosilicate glasses 1 The glass carrier is prepared from high-purity SiO2, H3BO3 and ZnO powders, and the 2 perovskite components were added into Cs2CO3, PbBr2 and KBr (CPB). The purity and supplier of 3 all reagents are given in Table 2. All experiments are conducted without toxic and harmful organic 4 reagents. All raw materials are first ground into a powder in an agate mortar and then transferred to 5 a corundum crucible. The powder is melted in a muffle furnace at 1200 °C for 15 min. The molten 6 glass is then poured into a preheated copper mold and immediately transferred to a muffle furnace 7 at 350 °C and held for 2 h to release stress. Finally, the precursor glass was heat treated near the 8 glass transition temperature to obtain CsPbBr3 PQDs multi-component glass. Stored at a heat 9 treatment temperature of 470 °C for 10 hours, a series of CsPbBr3 PQDs multi-component glass 10 samples were obtained. For further study, the resulting glass is ground into a powder or optically 11 polished. 12 Table 1. Glass compositions [xSiO2- (67-x) B2O3-16ZnO (x=35, 38, 41, 48, 58 mol%)] and the added 13 perovskite-related components. 14 Sample SiO2 B2O3 ZnO Cs2CO3 PbBr2 KBr 35Si 35 32 16 9 3 6 38Si 38 29 16 9 3 6 41Si 41 26 16 9 3 6 48Si 48 19 16 9 3 6 58Si 58 9 16 9 3 6 8CPB 38 29 16 8 2 4 9CPB 38 29 16 9 3 6 10CPB 38 29 16 10 4 8 11CPB 38 29 16 11 5 10 12CPB 38 29 16 12 6 12 9CPB-1.8 38 29 16 9 5.4 10.8 9CPB-2.1 38 29 16 9 6.3 12.6 9CPB-2.4 38 29 16 9 7.2 14.4 9CPB-2.7 38 29 16 9 8.1 16.2 9CPB-3.0 38 29 16 9 9 18 2.2 Fabrication of QiG@glass films 15 Glasses with composition 20B2O3-60TeO2-10ZnO-10Na2O were prepared by using analytical 16 grade B2O3, TeO2, ZnO, Na2CO3 as starting materials. Based on a certain stoichiometric ratio, the 17 starting materials were weighted and mixed together. It was thoroughly ground and placed in an 18  5  alumina crucible and then melted for 0.5 h at 950 °C in a muffle furnace. Subsequently, the melt 1 were poured into a preheated brass mold and annealed at 300 °C for 15 h. Glass samples were cut 2 and carefully polished to meet optical measurements. Each sample looks more transparent. 3 The slurries were mixed by suitable powder dosing: the prepared glass-stabilized CsPbBr3 4 PQDs powder, Sr2Si5N8 red phosphor, and tellurite glass matrix. All powders were mixed into 5 organic vehicle which composition were terpilenol and ethyl cellulose at 80 K for 12 h by 700 rpm. 6 The mixed slurry is spin coated onto the glass substrate (r = 20 mm) by scraping and then the 7 resultant samples were dried at 150 °C for 5 h in order to make the organic matter completely volatile. 8 Finally, QiG@glass film was obtained by sintering the glass film at 460 °C for 30 min.  9 Table 2. Purity and supplier of each starting reagent. 10 Start reagent Purity Supplier SiO2 GR Shanghai Maclin Biochemical Technology Co., LTD H3BO3 GR Shanghai Titan Technology Co., LTD ZnO AR, 99.0% Shanghai Titan Technology Co., LTD Cs2CO3 99.9% Shanghai Merrier Chemical Technology Co., LTD KBr AR, 99.0% Sinopharm Chemical Reagent Co. LTD PbBr2 99 % Shanghai Titan Technology Co., LTD TeO2 99.99% Chengdu Zhongjian Materials Optoelectronic Materials Co., LTD Na2CO3 AR, ≥ 99.8% Shanghai Titan Technology Co., LTD 2.3 Characterization 11 The phase purity of phosphor powders and QiG@glass firms was confirmed by using an X-ray 12 powder diffractometer (TD-3500, Dandong, China) with Cu Kα irradiation at 40 kV and 40 mA. 13 The microstructure and elemental mappings were observed by a field-emission scanning microscope 14 (SU70, Hitachi) equipped with an energy-dispersive X-ray spectroscope (EDS) system and 15 Transmission Electron Microscopy (FEI Tecnai F20). The photo-luminescence (PL) and photo-16 luminescence excitation (PLE) of the samples were measured using a spectrometer (Hitachi F-7000) 17 with a xenon discharge lamp. FS5 fluorescence spectrometer is standard equipped with absorption 18 detector, which can achieve fluorescence and UV testing functions on the same instrument at the 19 same time, so we tested the quantum yield by FS5. Decimal methods can also be applied to a wider 20 javascript:; 6  range of sample types and are the only reliable method for samples such as solid powder and thin 1 films. The test requires an integrating sphere that is coupled to the fluorescence spectrometer as a 2 test attachment. In absolute quantum yield testing, all light emitted by a sample is captured using an 3 integrating sphere, and the quantum yield is determined by comparing the number of photons 4 emitted to the number of photons absorbed. Such as formula (1): 5 𝜂 =𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑝ℎ𝑜𝑡𝑜𝑛𝑠 𝑒𝑚𝑖𝑡𝑡𝑒𝑑𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑝ℎ𝑜𝑡𝑜𝑛𝑠 𝑎𝑏𝑠𝑜𝑟𝑏𝑒𝑑                                               (1) 6 The difference in integral area between the sample and the reference indicates the number of the 7 absorbed photons. The emitted photons were determined by integrating the related emission band. 8 Test the blank curve with the blank sample that comes with the integrating sphere. The scattering 9 curve and the sample curve are combined to calculate the quantum yield. The optical properties of 10 the w-LED module are obtained in the integrating sphere, including chromaticity color coordinates, 11 correlated color temperature (CCT), color rendering index (CRI), luminous efficiency, and 12 electroluminescence (EL) emission spectroscopy (HAAS-2000).  13 3. Results and Discussion 14 3.1   Microstructure and luminescence of PQDs@glass 15  16 Fig. 1 (a-c) Photoluminescence spectra and PLQY of xSiO2- (67-x) B2O3-16ZnO (x=35, 38, 41, 17 48, 58 mol%) glass with different CPB components excited at 365 nm.  18 Fig. 1 shows the photoluminescence (PL) spectra and PLQYs of CsPbBr3 PQDs from 19 borosilicate samples under excitation at 365 nm and 450 nm. It can be seen that the well crystallized 20 CsPbBr3 PQDs formed in B39Si28 glass containing 9CPB-2.4 has the highest PLQY value 21 (88.06%). With the decrease of B/Si ratio, the emission intensity increases first and then decreases, 22 reaching the maximum value at Si38B29, and the change of quantum yield also presents the similar 23 trend. The photoluminescence of sample exhibits the narrow-band emission characteristics of 24 a) b) c)  7  quantum dot materials. It can be seen from Fig. 1(a) that the luminescence of CsPbBr3 PQDs doped 1 glass is controlled by changing the topological structure of the glass. The glass grid structure has an 2 important impact on the precipitation and growth of quantum dots from mother glass, which in turn 3 affects the luminescence performance. Based on our previous work, there exists an optimal B/Si 4 molar ratio that possesses the moderate glass rigidity, which can boost the precipitation of CPB 5 elements and accelerate the growth of nanocrystals from glass network[26]. Therefore, Si38B29 6 sample is selected as glass host to optimize CPB concentration (PL spectra shown in Fig. 1(b and 7 c))[27]. In order to compensate for the volatile loss of Br element during the melting procedure, 8 excess amounts of halogen compounds, PbBr2 and KBr, needed to be added to the raw material. 9 With the increase of doped concentration, more and more quantum dots polymerize and grow in 10 glass, resulting in an increase in PQDs concentration, it is worth noting that a moderate excess of 11 Br supplementation in raw materials is more conducive to the growth of PQD in glass. The results 12 show that the quantum efficiency of the sample reaches the maximum when the CPB concentration 13 is further increased to 9Cs2CO3−7.2PbBr2−14.4KBr mol%.   14 As showed in TEM image (shown in Fig. 2(a)), the CsPbBr3 PQDs are evenly dispersed in the 15 glass matrix, and their average particle size is 2.98 nm. High-resolution TEM (HRTEM) image (Fig. 16 2(b)) evidences homogeneous precipitation of CsPbBr3 PQDs with well-resolved lattice fringes with 17 high-crystallinity, which shows clear lattice fringes with an interplanar distance of 0.288 nm. The 18 lattice fringes have 0.288 nm interplanar distance that corresponds to the [200] lattice plane of the 19 cubic CsPbBr3[28,29]. It can be seen that the PQDs in the glass are different from the cubic form of 20 the colloidal PQDs prepared by wet chemistry, and the PQDs in the glass is a spherical form, which 21 may be due to the restriction effect of inorganic oxidized glass on the growth of PQDs. Elemental 22 mapping of these nanocrystals suggested that these nanocrystals were highly rich in Cs, Pb and Br. 23 In general, the precipitation of CsPbBr3 nanocrystals in the sample was confirmed.  24  8   1 Fig. 2 (a and b) TEM image of the CsPbBr3 PQDs@glass. (c) HRTEM micrograph of the CsPbBr3 2 PQDs@glass. (d-i) B, Si, Cs, Pb, and Br elemental mappings. 3 3.2.  Microstructure and luminescence of QiG@glass film. 4 QiG@glass films have high thermal stability compared to conventional organic encapsulation; 5 Good moisture resistance; It has the characteristics of corrosion resistance and high chemical 6 stability. The XRD patterns of quantum dot glass, red phosphor and QiG@glass samples are shown 7 in Fig. 3(a). The different peaks correspond to the Sr2Si5N8 and PQDs, which is in accord with that 8 of the pure Sr2Si5N8 phosphor and standard card of CsPbBr3 (PDF #75–0412), respectively. The 9 QiG@glass film has little effect on the phosphors, and the fluorescent crystal phase is intact in glass 10 matrix. Furthermore, the 9CPB-2.4 QiG@glass film was chosen to check the possible reaction 11 between as-prepared glass and the phosphor, SEM, EDS and EDS mapping were carried out. Fig. 12 3(b-h) indicates that the glass and phosphor powder are uniformly distributed in the tellurite glass 13 matrix. The moderate concentration of pores in film is beneficial to reducing the reflection of 14 incident light to improve the utility of pump light [30,31]. The cross section image (shown in Fig. 3(c)) 15 suggests the phosphor layer with a thickness of approximately 24.54μm has been well adhered on 16 the surface of silica glass substrate after sintering.  17 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.005101520  CountGrain diameter(nm)a) b) d) e) f) g) h) i) c)  9   1 Fig. 3 (a) The XRD patterns of quantum dot glass, red phosphor and QiG@glass samples. (b and 2 c) SEM of QiG@glass film. (d) EDS spectrum of QiG@glass film. (e-h) Mapping image of Te, N 3 and Cs.  4 We prepared a series of W-LEDs by changing the ratio of quantum dot glass powder to red 5 phosphor. To research the luminescence properties, the prepared QiG@glass film is assembled on 6 the top of the blue chip under the 450 nm irradiation with a drive current of 10 mA (Fig. 4 (b)). To 7 produce white light, we mixed the red phosphor Sr2Si5N8 with glass powder at the content sub-point 8 and then embedded in the tellurite glass to form a QiG@glass. The weight ratio of glass to 9 phosphorus is adjusted from 10:1 to 14:1. The resulting electroluminescence diagram and color 10 coordinates are shown in Fig. 4(a and c). According to EL spectrum and chromaticity diagram, the 11 ratio of glass to phosphor is 13:1, which is the best ratio to produce white light. As the proportion 12 of glass powder in QiG@glass increased, the 450 nm blue component in the spectrum increased, 13 and the light color changed from warm white to cold white, as shown in Fig. 4(c).  14 f ) g) b) c) e) d) a) h)  10   1 Fig. 4 (a) Optimum ratio electroluminescence diagram. (b) Schematic diagram of LED package. 2 (c) Color coordinates at different scales and real pictures. 3 Fig. 5(a) shows the excitation and emission spectra of the glass powder and phosphor used in 4 the experiment, respectively. It can be seen that the emission peak of the glass powder is located at 5 526 nm. It indicates that the emission spectrum of the glass powder and the excitation spectrum of 6 the red powder have a large area of spectral overlap. The emission spectrum of glass powder can 7 theoretically be reabsorbed by red powder and converted into red emission spectrum, which 8 improves the emission intensity of red light, and correspondingly reduces the probability of green 9 light transmitted out of the film to the space. QiG@glass films (the ratio of glass to red phosphor 10 power was 13:1) were prepared at a sintering temperature of 460 °C to 490 °C. As the sintering 11 temperature increased, the color of the sample gradually darkened, and the color rendering index 12 decreased from 87.2 to 55.7. The color temperature increased from 3920 K to 12821 K. The results 13 show that the sintering conditions of the QiG@glass film have a significant effect on the 14 performance of the red phosphor. This may be due to the instability of the crystal phase structure of 15 nitride in glass[32-37]. At a low sintering temperature of 460 °C, the thermal damage can be reduced 16 for better luminous performance. At this temperature, warm white light with high visibility can be 17 obtained.  18 tellurite glass red phosphor CsPbBr3 glass Blue LED mount 10：1 11：1 13：1 14：1 12：1 b) a) c)  11   1 Fig. 5 (a) Emission spectrum of glass powder and excitation spectrum of phosphor powder. (b) 2 The electroluminescence diagram of QiG@glass at different sintering temperatures. 3 3.3 The stability of QiG@glass film 4 The stability of QiG@glass is an important parameter for its applications. The PL temperature 5 dependence was investigated (Fig. 6(a)), showing the PL spectra of QiG@glass at eight typical 6 temperatures of 25, 50, 75, 100, 125, 150, 175 and 200 °C (298-473 K). With increasing of 7 temperature (solid lines), the PL intensity decreased and its peak wavelength was blue-shifted. 8 When the sample were cooled (dashed lines), the PL intensity and the shifted peak wavelength were 9 reversibly recovered. These characteristic temperature dependent PL intensity change and emission 10 peak shift have been commonly found in CsPbBr3 perovskite nanocrystals, which can be attributed 11 to the thermal expansion and phonon−electron interaction[19]. Furthermore, the long-term stability 12 for the QiG@glass samples was investigated by dipping them in water. PL spectra shows that there 13 is no obvious change of PL intensity (Fig. 6(c)) in water for 60 days. Under the protection of tellurite 14 glass and borosilicate glass, the emission intensity is basically unchanged after 60 days of immersion 15 in water. This result confirms that tellurite glass carriers and borosilicate glass are indeed effective 16 in protecting PQDs from decomposition.  17 a) b)  12   1 Fig. 6 (a) Temperature-dependent PL spectra (λex = 450 nm) for the QiG@glass in the 2 temperature range of 298-473 K. (b) Integral photoluminescence intensities of QiG@glass 3 specimens recorded during thermal cycling experiment. (c) PL spectra for QiG@glass 4 directly immersing in water for 60 days and inset is a photo of glass in water under the 5 illumination of a blue light chip. (d) Integrated photoluminescence intensities in water 6 stability.  7 The QIG@glass film was irradiated with a blue light of 300 mA forward current for 0, 3, 9, 21, 8 45, 93 h, equally its luminescence spectrum was tested (Fig. 7(a and b)), and the luminous intensity 9 only decreased by about 3%. By introducing oxygen into the tube furnace, the oxygen stability of 10 the film was studied by making the film stand in the oxygen environment for 0, 12, 48, 96 h. The 11 luminescence spectrum shows (Fig. 7(c and d)) with no significant change in luminous intensity. 12 Therefore, tellurite glass matrix can protect the stability of PQDs and phosphors effectively.  13  14 0       30      60 a) b) c) d)  13   1 Fig. 7 (a) PL spectra (λex = 450 nm) of QiG@glass under different duration blue light 2 irradiation (b) Integrated photoluminescence intensities in light stability. (c) PL spectra (λex = 450 3 nm) of QiG@glass under different duration oxygen conditions. (d) Integrated photoluminescence 4 intensities in oxygen stability. 5 4. Conclusions 6 We successfully deposited CsPbBr3 PQDs into borosilicate glass by melt quenching technique 7 and heat treatment. The quantum efficiency PLQY of CsPbBr3 reached 88.06% after the regulation 8 of various components in the glass. QiG@glass film was prepared by scraping and coating technique. 9 Tellurite glass with low melting point was double coated to protect the stability of phosphors. A red 10 phosphor emitting a wide spectrum was used to improve the color rendering index. The color 11 rendering index of single-luminescent center QiG@glass thin-film conversion W-LED device is up 12 to 87.2, the corresponding color temperature is 3920K, and the color gamut of 111.92% of the NTSC 13 standard.  14 Acknowledgement 15 Guoying Zhao acknowledges financial supported by Science and Technology Talents 16 a) b) d) c)  14  Development Fund for Young Middle-aged Teachers Fund, Collaborative Innovation Fund (No. 1 XTCX2022-03) of Shanghai Institute of Technology and Development of key technologies for the 2 preparation and application of high-performance rare earth fluorescent block materials (No. BFXT-3 2022-D0046). Jingshan Hou acknowledges financial supported by the National Natural Science 4 Foundation of China (No. 51902203). Yongzheng Fang acknowledges financial supported by the 5 National Natural Science Foundation of China (No. 51472162). 6 References  7 [1] Cai C, Wang X, Ling L, et al. 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Conflict of InterestCRediT authorship contribution statement Huanhuan Zhang: Conceptualization, Writing - Original Draft, Investigation. Jialing Ou: Methodology, Data Curation, Investigation. Guoying Zhao: Methodology, Writing – Review＆Editing. Jingshan Hou: Resources, Validation. Yufeng Liu: Resources, Formal analysis. Xin Qiao: Resources, Data curation. Zhongzhi Wang: Methodology, Resources. JiGuang Li: Resources. Yongzheng Fang: Funding acquisition, Supervision.  Author Statement