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Jing Yao, Lu Chen, Qi Zhu, [Ji‐Guang Li](https://orcid.org/0000-0002-5625-7361)

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This is the peer reviewed version of the following article: Pressureless sintering of LRH nanoplates on amorphous alumina for near-infrared GAP:Mn4+ transparent ceramic film, which has been published in final form at https://doi.org/10.1111/jace.18879. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. This article may not be enhanced, enriched or otherwise transformed into a derivative work, without express permission from Wiley or by statutory rights under applicable legislation. Copyright notices must not be removed, obscured or modified. The article must be linked to Wiley’s version of record on Wiley Online Library and any embedding, framing or otherwise making available the article or pages thereof by third parties from platforms, services and websites other than Wiley Online Library must be prohibited.[In Copyright](http://rightsstatements.org/vocab/InC/1.0/)

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[Pressureless sintering of LRH nanoplates on amorphous alumina for near-infrared GAP:Mn4+ transparent ceramic film](https://mdr.nims.go.jp/datasets/0e7ac50a-0da9-46f6-a716-cd741aafdbef)

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For Peer ReviewPressureless sintering of LRH nanoplates on amorphous alumina for near-infrared GAP: Mn4+ transparent ceramic filmJing Yaoa, Lu Chena, Qi Zhua*, Ji-Guang LibaKey Laboratory for Anisotropy and Texture of Materials (Ministry of Education), School of Materials Science and Engineering, Northeastern University, Shenyang, Liaoning 110819, ChinabResearch Center for Functional Materials, National Institute for Materials Science, Namiki 1-1, Tsukuba, Ibaraki 305-0044, Japan*Corresponding authorDr. Qi ZhuTel: +86-24-8367-2700E-mail: zhuq@smm.neu.edu.cnPage 1 of 24Journal of the American Ceramic SocietyJournal of the American Ceramic Society123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960mailto:zhuq@smm.neu.edu.cnFor Peer ReviewAbstractTransparent ceramics have become a research hotspot in the preparation of fluorescent materials in recent years because of their excellent physical and chemical properties and high transparency. Gadolinium aluminate, as a stable matrix material, is often doped with various active ions to obtain luminescence with different colors. However, it is very difficult to fabricate gadolinium aluminate transparent ceramics by a traditional method, although they are the charming solid lighting materials. Here, we developed a pressureless sintering method to prepare GdAlO3: Mn (GAP: Mn) transparent ceramic films, which were prepared by spin coating rare earth hydroxide (LRH) on amorphous alumina substrate and sintering at 1550 oC for 2 hours. Through the interface reaction, the Al2O3 reacts with Gd2O3 to form mesophase Gd4Al2O9 below 1550 oC. However, the final products are GdAlO3 at 1550 oC. The GAP: Mn4+ film exhibits a high transmittance of over 90%. Under UV excitation at 310 nm, the ceramic film outputs deep red and NIR emissions, which are both arising from the 2Eg-4A2g transition of Mn4+. Due to the electron traps arising from unequal valence substitution, the ceramic film exhibits a negative thermal quenching phenomenon. The ceramic film has a good luminescence thermal stability, because its emission intensity at 150 oC maintains over 72% that at room temperature. This work may pave a new way to fabricate transparent ceramics using rare earth hydroxides.Keywords: Transparent ceramics; GdAlO3; Mn4+; Interface reaction; Layered rare earth hydroxidePage 2 of 24Journal of the American Ceramic SocietyJournal of the American Ceramic Society123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960For Peer Review1. IntroductionThe perovskite family of materials has attracted extensive attention due to the various interesting properties such as ferroelectricity, photoluminescence, superconductivity, and magnetoresistance 1, 2. Perovskite (CaTiO3) was first discovered by Gustav Rose in 1839 and named after the Russian mineralogist L.A. perovskite 3. In recent years, a lot of researches have been done on the luminescence of solid perovskites, including luminescence in powders, single crystals, thin films, and amorphous materials. Metal halogenated perovskite materials have a wide range of applications in the fields of solar cells, photodetectors and light-emitting diodes 4, 5, 6. The most representative oxide perovskite material is CaTiO3. In 1997, Diallo et al. 7 reported the Pr3+ doped calcium titanate material for the first time, and they discussed and analyzed the red luminescence and the spectral properties of CaTiO3: Pr3+ phosphors in detail. After that, CaTiO3: Pr3+ materials were given a lot of research 8, 9, 10, and the ion types doped with CaTiO3 gradually increased, including Dy3+ doped white phosphors 11, Eu3+ doped red phosphors 12, Bi3+ doped yellow phosphors 13 and Sm3+ doped orange-red phosphors 14, etc. Due to the special structure of perovskite oxide (ABO3), many types of ions can substitute for A or B site, resulting in perovskite luminescent materials. Because of their stable structure and excellent optical properties, they have great research significance and value in the fields of light, electricity and magnetism. According to the investigation, most perovskite rare earth fluorescent materials are mainly concentrated in the three systems of GdAlO3, LaAlO3 and YAlO3, while the electrons in the 4f sublayer of Gd3+ are half filled, the 4f electrons of La3+ are fully filled, while Y3+ has no 4f electrons 15. Therefore, they are relatively stable as matrix materials, and can be incorporated into the body by different activators to obtain different types of luminescence. In recent years, there are abundant studies and reports on different types of YAlO3 and LaAlO3 as matrix materials, while there are relatively few studies on GdAlO3 as matrix materials. In 1995, Dorenbos et al. 16 reported the scintillation characteristics of GdAlO3 single crystals doped with different concentrations of Ce3+ grown by horizontal directional crystallization technology. In 1999, Jovanic et al. 17 Page 3 of 24Journal of the American Ceramic SocietyJournal of the American Ceramic Society123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960For Peer Reviewreported Cr3+ doped GdAlO3, which was expected to be a good pressure sensor. At that time, there were many researches on GdAlO3 matrix, while there were relatively few rare earth ion doped materials. In 2014, Wang et al. 18 reported the hydrothermal synthesis of GdAlO3: Eu3+ microcrystals and discussed the effect of reaction temperature on the formation of GdAlO3 and the fluorescence characteristics of GdAlO3: Eu3+. Shilpa et al. 19 synthesized GdAlO3: Eu3+, Bi3+ nano phosphors by solution combustion technology. The addition of Bi3+ makes the emission of phosphors change from orange red to dark red, which is expected to be used as the red component in WLED. Up to now, the activated ions used by GdAlO3 as matrix materials are mainly Eu3+ 19, 20 and Ce3+ 16, 17, 18, 19, 20, 21, and a small number include Yb3+ (yellow), Tb3+ (blue and green), Pr3+ (blue and red), Er3+ (green), Cr3+ and Mn4+ (near infrared). Moreover, most of the studies are carried out to characterize the fluorescence properties by making GdAlO3 nanocrystals or phosphors, and there are few reports on GdAlO3 transparent ceramics.The unit cell structure of GdAlO3 (GAP) is a tetrahedron (a=5.305 Å, b=7.448 Å, c=5.254 Å), which belongs to orthogonal ABO3 perovskite structure. GdAlO3 is a distorted perovskite. Gd3+ changes from 12 to 8 coordination with oxygen atoms in the ideal perovskite, and Al3+ still maintains 6 coordination with oxygen atoms. Its space group is Pbnm, which deviates from the cubic space group Pm3m due to the distortion of [BO6] octahedron. The [AlO6] octahedral cluster is arranged along the c crystal axis, and the [GdO8] polyhedron is connected with the [AlO6] octahedron in a collinear or coplanar manner 22. This special structure makes it possible optimize or realize the tunable luminescence characteristics through a variety of doping or composition modification.Fluorescent materials are usually prepared in the form of powders or transparent ceramics. Due to its excellent physical and chemical properties, high transmittance and easy preparation into various shapes, transparent ceramics have better performance in the fields of high-power and high-density devices, as well as light-emitting devices that have special requirements for their appearance and need to be integrally molded. It is more and more favored by modern society at present. Page 4 of 24Journal of the American Ceramic SocietyJournal of the American Ceramic Society123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960For Peer ReviewTransparent ceramics can be widely found in solid-state lasers, transparent armor, scintillators, optical components, and solid-state lighting 23, 24, 25, 26, 27, 28.Manganese, a non-rare earth element with multiple oxidation states, is considered a promising alternative to europium or chromium for the design of red to near-infrared sustained-emitting phosphors. In recent years, Mn4+-activated phosphors have received extensive research and attention 29, 30, 31, 32, 33. Compared with rare earth ions, it is cheaper, and Mn4+ is greatly affected by the crystal field and will emit a strong deep red or near-infrared according to the crystal field. Mn4+-doped phosphors have been used in the lighting industry as a red component, usually exhibiting broadband excitation and sharp red emission. On the other hand, Mn4+ can emit near-infrared light, which also has potential application prospects in biomedical imaging and other fields 34. The emission of manganese mainly depends on its valence state, ion distribution and local coordination environment. The Mn4+ ions with the 3d3 electronic configuration can be stably located in an octahedral symmetric environment, and their optical properties are strongly influenced by the local environment and the covalency of the Mn-ligand bond 34, 35. The electron-phonon coupling and covalency of Mn4+ ligand bonds could lead to strong or weak crystal field, which depends on the host lattice and can realize the desired tunable luminescence. Due to the feasible substitution between Al3+ (0.535 Å, CN=6) and Mn4+ (0.53 Å, CN=6) ions, gadolinium aluminate (GdAlO3) with perovskite crystal structure is a suitable host for Mn4+ doping.In this work, a novel strategy was proposed for the growth of GdAlO3: Mn4+ (GAP: Mn4+) transparent ceramic films on the amorphous alumina substrate by an interfacial reaction. Characterization of the films was achieved by XRD, FT-IR, SEM, UV-Vis-NIR, PLE/PL spectroscopy, temperature-dependent PL spectroscopy, and luminescence decay analysis. The ceramic film outputs deep red and NIR emissions and exhibits a negative thermal quenching behavior. The transparent film with a high transmittance has a good luminescence thermal stability. The outcomes may broaden the application of rare earth hydroxide and play a demonstration role on other transparent ceramics.Page 5 of 24Journal of the American Ceramic SocietyJournal of the American Ceramic Society123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960For Peer Review2. Experimental section2.1 SynthesisThe starting material for rare earth source is Gd2O3 (99.99% pure, Huizhou Ruier Rare-Chem. Hi-Tech. Co. Ltd, Huizhou, China) and the starting material for manganese source is Mn(NO3)2 (50 wt%). Manganese nitrate, ammonia hydroxide (NH4OH, 25 wt%), nitric acid (HNO3, 67 wt%) and anhydrous ethanol (C2H5OH, 99.7%) were purchased from Sinopharm Chemical Reagent Co. Ltd. The aqueous solution of Gd(NO3)3 was made by dissolving the powder of Gd2O3 in nitric acid.Synthesis of LRH and LRH: Mn crystals. In a typical synthesis, a mixed aqueous solution containing 2 mmol of Gd(NO3)3 and Mn(NO3)2 (Gd: Mn molar ratio of 99.1:0.9) was prepared under magnetic stirring at room temperature. After titrated with NH4OH solution, the pH value of colloidal suspension was adjusted to ~7. Then the white suspension was transferred to a Teflon lined stainless-steel autoclave of 100 mL capacity for hydrothermal reaction. The final product was collected via centrifugation, followed by washing with deionized water (three times) and anhydrous ethanol (one time). Gd-based LRH in absence of Mn was prepared in the same way.Fabrication of GAP transparent ceramic film. The LRH crystals were put on a transparent amorphous alumina substrate by spin coating, followed by calcined at 800 oC, 1000 oC, 1300 oC and 1550 oC for 2 h, respectively. GdAlO3 (GAP) transparent ceramic films directly growed on the amorphous alumina substrate through an interfacial reaction.2.2 CharacterizationX-ray diffractometry (XRD, Model SmartLab, Rigaku, Tokyo, Japan) was used for phase identification under 40 kV/40 mA, using nickel filtered Cu-Kα radiation (λ = 0.15406 nm) with a scanning speed of 6.0o/2θ per minute and scanning range of 5o-60o. Fourier transform infrared spectroscopy (FT-IR, Model Nicolet iS5, Thermo Fisher Scientific, Madison, WI, USA) was conducted by the standard KBr method. Field emission scanning electron microscopy (FE-SEM, Model JSM-7001F, JEOL, Tokyo) was used to analyze the morphology and microstructure of the products under an acceleration voltage of 15 kV. At room temperature, photoluminescence were Page 6 of 24Journal of the American Ceramic SocietyJournal of the American Ceramic Society123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960For Peer Reviewanalyzed by a fluorescence spectrophotometer (Model FP-8600, JASCO, Tokyo) equipped with a 150 W Xe-lamp as the excitation source and an integrating sphere (Model ISF-513, JASCO, Tokyo). UV-vis-NIR spectrophotometer (UV-3600 plus, Shimadzu, Kyoto, Japan) was used to analyze the transmittance of the samples at room temperature.3. Results and discussion3.1 Synthesis and characterization of LRH and LRH: Mn crystalsBased on our previous research, LRH crystals were synthesized by a hydrothermal reaction 36, 37, 38. Figure 1a shows the XRD patterns of LRH and LRH: Mn. The hydrothermal products are layered rare-earth hydroxides in a pure phase form, because all the diffraction peaks can well match to the reported data 36, 37, 38. The (00l) diffraction peaks, such as (002) and (004), show the unique layered structure, while the appearance of (hk0) diffraction peak, such as (220), confirms the well-developed layered structure of the compounds. No other impurities are formed, which implies that single phases of Gd LRH and Gd/Mn binary LRH solid solution were successfully synthesized. Thus, incorporation of manganese ions has no obvious effect on the XRD diffraction peak of LRH (Figure 1a).Figure 1b shows the FT-IR spectra of LRH and LRH: Mn. The absorption peak at the range of 3500~3750 cm-1 originates from the vibration of the hydroxyl (OH-), and the absorption peaks at the range of 3000~3500 cm-1 and at ~1631 cm-1 are owing to the O-H and H-O-H stretching vibration of H2O, respectively 39, 40. The appearance of these vibrations directly confirms the existence of molecular water in layered rare earth hydroxides. The absorption peak at ~1358 cm-1 in LRH and LRH: Mn is attributed to the bending vibration of NO3- 39, 40. XRD and FT-IR spectra both show that the incorporation of manganese ions has no significant effect on the structure of LRH. Figure 1c, d shows the FE-SEM images of LRH and LRH: Mn, respectively. The nanoplates in Figure 1c are hexagonal platelets of about 200 nm with smooth surface and clear edge. The crystallinity of LRH becomes worse after manganese ion doping (Figure 1d), accompanied by rough surfaces and fuzzy edges. However, the Page 7 of 24Journal of the American Ceramic SocietyJournal of the American Ceramic Society123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960For Peer Reviewnanoplates of LRH and LRH: Mn with two- dimensional morphology are suitable for fabrication of functional films, which may be comparable with the exfoliated nanosheets 37, 41.3.2 Characterization and structure evolution of the ceramic filmIn absence of pressure, GAP and GAP: Mn transparent ceramic films directly growed on the amorphous alumina substrate. Figure 2 is the schematic diagram of preparing GAP ceramic film, which shows the whole process of the experiment. In order to explore the formation mechanism of GAP, the prepared LRH precursor nanoplates were coated on the surface of amorphous alumina and calcined at 800 oC, 1000 oC, 1300 oC, 1550 oC for 2 hours, respectively. Figure 3 shows the XRD patterns of GAP film and GAP: Mn film at different temperatures. The XRD results indicate that only cubic structured Gd2O3 was preferentially formed on the substrate at 800 oC, and Al2O3 did not react with rare earth oxide at the interface. When the temperature is rising to 1000 oC, although the main calcined products are also Gd2O3, there is a small trace of Gd4Al2O9, mainly due to that a few Al2O3 reacted with Gd2O3 at the interface to form the intermediate phase of Gd4Al2O9 following the reaction as below:Gd2O3 + Al2O3 → Gd4Al2O9             (1)When the temperature increased to 1300 oC, a mixture of Gd2O3, Gd4Al2O9 and GdAlO3 was found, indicating increased amount of Al2O3 reacted with Gd2O3 though the interfacial reaction at this temperature. Obviously, increasing the temperature yielded fewer amounts of Gd2O3 and increased amount of gadolinium aluminate, such as Gd4Al2O9 and GdAlO3. The alumina reacted with Gd2O3 and Gd4Al2O9 to form GdAlO3, which is the gadolinium aluminate with higher aluminum content. The reaction follows the equation as below: Gd2O3 + Al2O3 → Gd4Al2O9              (2)Gd4Al2O9 + Al2O3 → GdAlO3             (3)Increasing the calcination temperature up to 1550 oC only yielded GdAlO3 (termed as GAP), indicating the temperature to form GAP is at higher than 1300 oC (Figure 3). The XRD pattern of GAP: Mn is consistent with GAP, both of which are pure GAP Page 8 of 24Journal of the American Ceramic SocietyJournal of the American Ceramic Society123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960For Peer Reviewphase, confirming that manganese ions are successfully incorporated into the GAP matrix.Figure 4 is SEM morphology of the films calcined at various temperatures. At 800 oC, LRH like particles are found in the film (Figure 4a). Increasing the temperature to 1000 oC, the film is composed of small particles with fuzzy edges (Figure 4b). However, the film is composed of dense grains at 1300 oC, and most grains have sizes of 300-500 nm (Figure 4c). There is no observation of particles in the film. The grains grow up to 1-2 μm with increasing the temperature to 1550 oC (Figure 4d). However, the grain size of bulk ceramic fabricated through the traditional high-temperature reaction is about 10-30 μm 42, 43, 44, 45. Because the two-dimensional morphology restricted the grain growth during the interface reaction, obviously smaller grain size is found for the ceramic films. Also due to the low temperature of 1550 oC and short reaction time of 2 hours for the interface reaction, the ceramic film has the small grain sizes, comparing with that for the bulk ceramic, which is fabricated by the traditional reaction at the high temperature of 1700 oC-1800 oC through vacuum sintering 42, 43, 44, 45.The effect of calcination temperatures (800 oC, 1000 oC, 1550 oC) on the element distribution of Gd and Al for the films on Al2O3 substrate is analyzed in Figure 5. Because the main phase is Gd2O3 at 800 oC, Gd is found for the film along with a small trace of Al, which is arising from the Al2O3 substrate. Elevating the temperature resulted in the Gd content decreased from ~97.71% at 800 oC to ~72.82% at 1000 oC, and then to ~45.51% at 1550 oC. But the Al content increased from ~2.29% at 800 oC to ~27.18% at 1000 oC, and then to ~54.49% at 1550 oC. The higher the temperature is, the more Al2O3 participates in the interface reaction. The Al2O3 reacts with Gd2O3 to form GdAlO3 at 1550 oC, but the products are Gd2O3 and the mesophases of Gd4Al2O9 at the temperature lower than 1550 oC. Closely observation finds that the Al content at various temperatures is a little higher than that for the crystallization phases. For example, the Gd: Al molar ratio for GdAlO3 is 1:1, but the test result is 1:1.2 for the film calcined at 1550 oC. Because the amorphous Al2O3 from the substrate is excess for the interface reaction, the Al content is higher than that for the target Page 9 of 24Journal of the American Ceramic SocietyJournal of the American Ceramic Society123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960For Peer Reviewcomposition.Figure 6 shows the EDS-mapping results and FE-SEM images of the ceramic film cross section. According to the FE-SEM images, the thickness of the film is about 600-800 nm. EDS-mapping shows that the Al and Gd content change abruptly at the interface, which confirms the existence of GdAlO3 film on Al2O3 substrate. The changed area is in good agreement with the thickness of ceramic film. The above results show that GdAlO3 ceramic film with uniform distribution and reliable composition were successfully prepared through the interface reaction.3.3 Luminescence and negative thermal quenching behavior of GAP: Mn4+ transparent ceramic filmFigure 7a, b shows photoluminescence excitation (PLE) and photoluminescence emission (PL) spectra of GAP: Mn4+ transparent ceramic film. The PLE spectrum of GAP: Mn4+ film monitored at 698 nm is mainly divided into a strong excitation bands (250-350 nm) centered at 310 nm and a weak excitation bands near 400 nm (Figure 7a). The broad excitation bands at 290 nm, 323 nm and 401 nm are attributed to the charge transfer band of Mn4+-O2-, the 4A2g-4T1g and 4A2g-2T2g transitions of Mn4+, respectively 46. Under the excitation of 310 nm ultraviolet light, the PL spectrum shows three peaks at 682 nm, 698 nm and 719 nm (Figure 7b). Due to the electron phonon coupling of Mn4+ in the main body, there is a partially allowed spin forbidden 2Eg-4A2g transition (698 nm) 47, and the related phonon sideband vibration of Mn4+ in MnO6 octahedron. Figure 7c is the mechanism diagram of luminescence of GAP: Mn4+. Under the excitation of ultraviolet light, the electrons are excited from the ground state energy level 4A2g to the Mn4+-O2- charge transfer band, and the excited state energy levels 4T1g and 2T2g. Then they transfer to the 2Eg energy level through non radiative relaxation, and finally fall back to the ground state 4A2g, which contribute to the excellent near-infrared light output. Figure 7d shows the CIE coordinate diagram calculated from the PL spectral data of GAP: Mn4+. It can be observed that the color coordinate value of the sample is (0.730, 0.270), which is located at the deep red area of the CIE diagram, which is consistent with the PL Page 10 of 24Journal of the American Ceramic SocietyJournal of the American Ceramic Society123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960For Peer Reviewspectrum. Because the emission peaks are at 650-750 nm, which are in visible and NIR wavelength range, the ceramic film both outputs deep red and NIR emissions. The inset in Figure 7d shows the photo of GAP: Mn4+ ceramic film under real-time ultraviolet excitation, confirming that the ceramic film exhibits deep red emission.Figure 8a shows the transmittance curve of the prepared GAP: Mn4+ ceramic film and its appearance under daylight. There is broad and intense band at 250-400 nm in the transmittance curve, which is assigned to the absorption of Mn4+-O2- charge transfer, 4A2g-4T1g and 4A2g-2T2g transitions of Mn4+ respectively. At the visible wavelength range of 400 nm-650 nm, the ceramic film exhibits a transmittance of over 90%, while the transmittance of bare amorphous alumina substrate is about ~99.5%. Under the amorphous alumina coated with ceramic film, the words can also be clearly observed (inset in Figure 8a), further confirming that high transmittance of GAP: Mn4+ ceramic film. Figure 8b shows the fluorescence decay curve of GAP: Mn4+ ceramic film and the data of the curve could be fitted into a single exponential. The determined fluorescence lifetime of the sample is about 1.656 ms according to the following formula:= exp( / )I A t B                              (4)where τ is fluorescence lifetime (ms), t is decay time (ms), I is fluorescence intensity, A and B are constants. Most lifetimes for Mn4+ activated phosphors are reported at the value range of 1.259-4.13 ms, and the calculated lifetime of the ceramic film falls in the range 48, 49, 50, 51.   In order to evaluate the luminescent performance of transparent ceramic films, temperature-dependent PL spectra ranging from 25 oC to 300 oC were analyzed in Figure 9a. The shape and the position of all peaks in the emission spectra do not significantly change with the increased temperature, but the emission intensity of the peaks decreases. The relative integral intensity of the emission peaks at various temperatures is summarized in Figure 9b. It can be observed that the fluorescence intensity of the PL peak shows a trend of increasing first and then decreasing. This negative thermal quenching effect is caused by the electron trap arising from the Page 11 of 24Journal of the American Ceramic SocietyJournal of the American Ceramic Society123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960For Peer Reviewunequal valence substitution between the tetravalent manganese ions and the trivalent aluminum ions. As shown in Figure 9c, the electrons are excited by ultraviolet light from the ground state energy level to the excited state energy level, and the electron traps capture the electrons from the excited state energy level through tunneling 52. The captured electrons are released back to the excited state by heating processing, and the excited state obtains the released electrons to compensate for the loss of thermal fluorescence quenching. However, with the further increase of temperature, the captured electrons are empty, and the fluorescence intensity cannot be compensated, so the emission intensity decreases naturally. With the increase of temperature, the PL emission peak at 150 oC still maintained the fluorescence intensity more than 72% that at room temperature. The above results show that the GAP: Mn4+ transparent ceramic film has a good thermal stability under the excitation of 310 nm UV light.4. ConclusionIn this work, a novel strategy for the synthesis of GAP and GAP: Mn4+ transparent ceramic films was reported, that is, the ceramic films could be successfully prepared by an interfacial reaction of LRH and LRH: Mn nanoplates on the amorphous alumina substrate. Characterization of the films was achieved by XRD, FT-IR, SEM, UV-Vis-NIR, PLE/PL spectroscopy, temperature-dependent PL spectroscopy, and luminescence decay analysis. Phase evolution of the film was analyzed at the temperature range from 800 oC to 1550 oC. The higher temperature makes more Al2O3 gradually participate in the interface reaction, and react with Gd2O3 to form mesophase Gd4Al2O9, and finally to form GdAlO3 at 1550 oC. Due the two-dimensional restricted grain growth, the grain size of the film is about 1-2 μm. The GAP: Mn4+ film exhibits a high transmittance of over 90%. Under the excitation of 310-nm ultraviolet light, GAP: Mn4+ film exhibits three emission peaks at 682 nm, 698 nm and 719 nm, arising from the 2Eg-4A2g transition of Mn4+. Therefore, the ceramic film outputs deep red and NIR emissions. Because of unequal valence substitution between the tetravalent manganese ions and the trivalent aluminum ions, Page 12 of 24Journal of the American Ceramic SocietyJournal of the American Ceramic Society123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960For Peer Reviewthe ceramic film exhibits a negative thermal quenching phenomenon. The emission intensity of the ceramic film at 150 oC maintains over 72% that at room temperature, indicating it has a good luminescence thermal stability.NotesThe authors declare no competing financial interest.AcknowledgementsThis work was supported in part by the Natural Science Foundation of Liaoning Province (Grant 2020-MS-081), and National Natural Science Foundation of China (Grant 51302032, 51972047, 52172112).References1. C.C. Stoumpos, C.D. Malliakas, J.A. Peters, Z. Liu, M. Sebastian, et al. Crystal growth of the perovskite semiconductor CsPbBr3: a new material for high-energy radiation detection. Cryst Growth Des. 2013;13:2722-2727.2. S. Wang, Z. Liu, J.A. Peters, M. Sebastian, S.L. Nguyen, et al. Crystal growth of Tl4CdI6: a wide band gap semiconductor for hard radiation detection. Cryst  Growth Des. 2014;14:2401-2410.3. Z. Cheng, J. Lin. Layered organic–inorganic hybrid perovskites: structure, optical properties, film preparation, patterning and templating engineering. CrystEngComm. 2010;12:2646-2662.4. P. Tockhorn, J. Sutter, R. Colom, L. Kegelmann, A. Al-Ashouri, et al. Improved quantum efficiency by advanced light management in nanotextured solution-processed perovskite solar cells. ACS photonics. 2020;7:2589-2600.5. H. Wang, R. Haroldson, B. Balachandran, A. Zakhidov, S. Sohal, et al. Nanoimprinted perovskite nanograting photodetector with improved efficiency. ACS nano. 2016;10:10921-10928.6. D. Yang, G. Zhang, R. Lai, Y. Cheng, Y. Lian, et al. 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J Eur Ceram Soc. 2021;41:735-740.46. S. Li, Q. Zhu, X. Li, X. Sun, J.-G. Li. Near-infrared emitting microspheres of LaAlO3: Mn4+: defects engineering via Ge4+ doping for greatly enhanced luminescence and improved afterglow. J Alloys Compd. 2020;827:154365.47. X. Li, W. Li, B. Hou, M. Jia, Y. Xu, et al. Investigation of enhanced far-red emitting phosphor GdAlO3: Mn4+ by impurity doping for indoor plant growth LEDs. Physica B: Condensed Matter. 2020;581:411953.48. R. Cao, W. Luo, Q. Xiong, A. Liang, S. Jiang, et al. Synthesis and luminescence properties of novel red phosphors LiRGe2O6: Mn4+ (R= Al or Ga). J Alloys Compd. 2015;648:937-941.Page 17 of 24Journal of the American Ceramic SocietyJournal of the American Ceramic Society123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960For Peer Review49. W. Lü, W. Lv, Q. Zhao, M. Jiao, B. Shao, et al. A novel efficient Mn4+ activated Ca14Al10Zn6O35 phosphor: application in red-emitting and white LEDs. Inorg Chem. 2014;53:11985-11990.50. Y. Wang, C. Yu, Y. Zhou, E. Song, H. Ming, Q. Zhang. Mn4+ doped narrowband red phosphors with short fluorescence lifetime and high color stability for fast-response backlight display application. J Alloys Compd. 2021;855:157347.51. X. Wu, Y. Yang, S. Gai, L. Liu, Z. Zhou, et al. Enhancing photoluminescence properties of Mn4+‐activated Sr4−xBaxAl14O25 red phosphors for plant cultivation LEDs. J Am Ceram Soc. 2019;102:7386-7396.52. Z. Pan, Y.-Y. Lu, F. Liu. Sunlight-activated long-persistent luminescence in the near-infrared from Cr3+-doped zinc gallogermanates. Nat Mater. 2012;11:58-63.Page 18 of 24Journal of the American Ceramic SocietyJournal of the American Ceramic Society123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960For Peer ReviewFigure 1. (a) XRD patterns, (b) FT-IR spectra, and (c, d) FE-SEM morphologies of LRH and LRH: Mn. Figure 2. Schematic illustration of the phase evolution of ceramic film during the sintering process.Page 19 of 24Journal of the American Ceramic SocietyJournal of the American Ceramic Society123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960For Peer ReviewFigure 3. XRD patterns of the film calcined at different temperatures.Figure 4. SEM morphologies of the film calcined at different temperatures.Page 20 of 24Journal of the American Ceramic SocietyJournal of the American Ceramic Society123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960For Peer ReviewFigure 5. EDS elemental mapping analysis of the film calcined at different temperatures.Figure 6. (a) EDS elemental mapping and (b) SEM morphologies of the cross section of GAP ceramic film.Page 21 of 24Journal of the American Ceramic SocietyJournal of the American Ceramic Society123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960For Peer ReviewFigure 7. (a, b) PLE and PL spectra, (c) luminescence mechanism, and (d) CIE chromaticity diagram of GAP: Mn4+ ceramic film. Figure 8. (a) Transmittance curve of GAP: Mn4+ ceramic film and (b) Fluorescence decay curve for the 708 nm emission of GAP: Mn4+ ceramic film.Page 22 of 24Journal of the American Ceramic SocietyJournal of the American Ceramic Society123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960For Peer ReviewFigure 9. (a) Temperature-dependent PL spectra of GAP: Mn4+ ceramic film, (b) relative integral intensity of 698-nm emission, and (c) schematic diagram of fluorescence negative thermal quenching mechanism.Page 23 of 24Journal of the American Ceramic SocietyJournal of the American Ceramic Society123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960For Peer Review Graphic abstract 399x299mm (300 x 300 DPI) Page 24 of 24Journal of the American Ceramic SocietyJournal of the American Ceramic Society123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960