# Fileset

[VIS_NIR_barcodes_MDR.pdf](https://mdr.nims.go.jp/filesets/06296208-593a-4235-b702-fce7bc791471/download)

## Creator

[Barun Kumar Barman](https://orcid.org/0000-0002-9894-1890), [Keisuke Watanabe](https://orcid.org/0000-0002-4285-2135), Kenzo Deguchi, [Shinobu Ohki](https://orcid.org/0000-0002-7357-3833), [Kenjiro Hashi](https://orcid.org/0000-0002-0320-4768), [Atsushi Goto](https://orcid.org/0000-0002-9472-4098), [Tadaaki Nagao](https://orcid.org/0000-0002-6746-2686)

## Rights

[Creative Commons BY Attribution 4.0 International](https://creativecommons.org/licenses/by/4.0/)

## Other metadata

[Chameleonic Color‐Variable Microbead Emitters for Multilevel Spectroscopic Encryption from Visible to Infrared Wavelengths](https://mdr.nims.go.jp/datasets/be54385f-e39a-4d98-827c-8ed36d6a2570)

## Fulltext

Chameleonic Color-Variable Microbead Emitters for Multilevel Spectroscopic  Encryption from Visible to Infrared WavelengthsBarun Kumar Barman\*, Keisuke Watanabe, Kenzo Deguchi, Shinobu Ohki, Kenjiro Hashi,  Atsushi Goto, Tadaaki Nagao\*Dr. B. K. Barman, Dr. K. Watanabe, Dr. T. NagaoResearch Center for Materials Nanoarchitectonics (MANA)National Institute for Materials Science (NIMS),Tsukuba, Ibaraki 305-0044, JapanE-mail: BARMAN.Kumarbarun@nims.go.jp, [NAGAO.Tadaaki@nims.go.jp](mailto:NAGAO.Tadaaki@nims.go.jp)Dr. Deguchi, Dr. S. OhkiResearch Network and Facility Services Division, National Institute for Materials Science  (NIMS), Tsukuba, Ibaraki 305-0003, JapanDr. K. Hashi, Dr. Atsushi GotoResearch Network and Facility Services Division, National Institute for Materials Science  (NIMS), Tsukuba, Ibaraki 305-0003, JapanDr. T. NagaoDepartment of Condensed Matter Physics, Graduate School of ScienceHokkaido University Sapporo, Hokkaido 060-0810, JapanKeywords: Microresonator, photoluminescence, near infrared, whispering gallery mode,  photonics encryption, microbarcodes.Light emission mediated by whispering-gallery-mode (WGM) assumes distinct sharp resonant  peaks, providing a unique spectral signature for photonic barcoding, that make them highly  advantageous for compact microtagging systems. Most existing photonic barcodes are limited  to visible wavelengths, restricting their tagging potential. Achieving precise control over light  emission covering from the visible (VIS) to the near-infrared (NIR) region using “a single  object made of one kind of material” has been a significant challenge. Here, we report a scalable,  gram-scale synthesis of multicolor emitting carbonized polymer microspheres (MECPMs) via  a facile hydrothermal process. These spherical microcavities, containing extended π-conjugated1[mailto:NAGAO.Tadaaki@nims.go.jp](mailto:NAGAO.Tadaaki@nims.go.jp)polycyclic aromatic hydrocarbons (PAHs), exhibit broadband light emission spanning in the  entire VIS-NIR wavelength region. Leveraging their excitation-dependent photoluminescence  (PL), a single MECPM can show colour adaptable WGM-based white-light-emission (WLE)  throughout the VIS-NIR region, generating both visible and invisible microbarcodes by simply  adjusting the excitation wavelength. Compared with conventional polymer- or oxide-based  microcavities, MECPMs demonstrate enhanced chemical stability against acids and organic  solvents, remarkable spectral tunability, and powerful capabilities for photonic encryption.  Their ecofriendly, metal-free “chameleonic” photonic functionality thus provides a robust  platform for anti-counterfeiting, micro tagging and labelling, and next-generation photonic  security systems. Our invention paves the way for innovative photonic encryption via  information encoding and transmission across the VIS-NIR spectral regions.1\. IntroductionThe rising demand for secure labeling and anti-counterfeiting solutions has led to significant  advancements in miniaturized authentication technologies. Counterfeit goods pose a severe  global economic challenge, resulting in financial losses of hundreds of billions of dollars  annually while also undermining brand trust and consumer safety.\[1-3\] To combat this issue,  photoluminescent barcoding has emerged as a promising approach, enabling rapid, reliable  identification through visible or near-infrared (NIR) emissions.\[4, 5\] Various materials, including  organic dyes,\[6, 7\] rare-earth (RE) doped phosphors,\[8, 9\] polymer microparticles,\[4, 10\] RE- coordinated polymers and metal organic farmwork (MOF),\[11-14\] quantum dots (QDs),\[15\] carbon  dots (CDs),\[16\] and inorganic nanostructures,\[17\] have been explored for barcode generation.  Organic dyes are cost-effective and widely available but suffer from broad emission profiles,  making them susceptible to counterfeiting.\[18-20\] Semiconductor-based barcoding, particularly  using one-dimensional segmented structures with tunable optical properties, which still suffers  with broad emission spectrum and limited barcoding capacity.\[21-23\] However, their toxicity and  potential energy transfer issues when densely packed limit their applicability. RE-based  luminescent materials, known for their photostability, long fluorescence lifetimes, and distinct  emission lines, have also been utilized.\[9, 24\] Despite these advantages, their relatively simple  optical signatures make them vulnerable to duplication, and their reliance on RE elements raises  concerns regarding sustainability and toxicity. \[21, 25, 26\]2Photonic barcodes, leveraging optical resonances to encode data via distinct spectral  signatures, present an powerful alternative for secure microlabeling.\[27, 28\] These barcodes  operate by precisely controlling the resonance frequencies of microresonators, enabling unique  optical signals that are challenging to replicate.\[29\] Among these, whispering-gallery-mode  (WGM) microcavities stand out due to their exceptional light confinement properties. The  curved geometry of these microstructures facilitates total internal reflection (TIR), generating  well-defined optical resonances observable as sharp peaks in the photoluminescence (PL)  spectrum through transverse electric (TE) or transverse magnetic (TM) modes.\[30, 31\] Each mode  serves as an individual “bar” in the barcode, allowing the generation of highly complex,  miniaturized microbarcodes. Even slight variations in microcavity size, often below the  diffraction limit, can induce detectable spectral shifts, leading to distinctive and complex optical  signatures capable of carrying encoded barcode’s information.\[32\] These amplified PL  characteristics serve as unique identifiers when tagged on materials, making them highly  suitable for unclonable anti-counterfeiting applications. Traditionally, fluorescent dyes,\[33-35\]  semiconductor quantum dots,\[36\] -conjugated polymers,\[37, 38\] carbonized polymer  microspheres,\[39\] and nanographene \[40\] are employed as gain materials within spherical  microcavities. Recently, a strategy was developed to construct dual-stimuli-responsive photonic  barcodes based on organic molecules and perovskite quantum dot (PQD)-doped polymer WGM  microcavities for covert and overt anti-counterfeiting via light-controlled acidichromism or  swelling-deswelling mechanisms. \[7, 41\] However, most photonic microbarcodes reported so far  are limited to the visible wavelength region. Developing microcavities that emit across the  visible to near-infrared (VIS-NIR) spectrum remains an ambitious challenge, that liberate us  from relying on toxic narrow-bandgap semiconductors and synthetic metal complexes.Figure 1. Schematic illustration of multilayer encrypted microbarcodes generation, enabling  both visible to NIR photonics encoding for secure product authentication.3To address these these serious limitations, we propose a novel “Chameleon” microcavity  architecture. This system allows the optical resonances of a single material to be dynamically  tuned across the VIS-NIR range simply by varying the excitation wavelength. This concept  draws inspiration from chameleons, which achieve dynamic color changes through the vertical  arrangement of multiple pigment cells in their skin, responding to external factors such as light  intensity, temperature, humidity, and even emotional states.\[42, 43\] Similarly, this Chameleon- inspired microcavity enables the generation of encrypted photonic microbarcodes that function  in both visible (overt) and near-infrared (covert) spectral regions. This approach introduces a  promising direction for multilevel optical tagging and anti-counterfeiting technologies, an  unexplored area with considerably rich application and high security.The “Chameleon” microcavity based on white light emitting carbonized polymer microspheres  (WCPM) are produced on a gram scale through a simple, hydrothermal synthesis process  involving the crosslinking of natural peptides. During the formation, extended π-conjugated  polycyclic aromatic hydrocarbons (PAHs) become embedded within the structure, enhancing  their PL and enabling broadband emission from the VIS-NIR regions. This WCPM-based  microresonator functions like optical “chameleons”, with tunable emission color that shift  across the VIS-NIR range simply by changing the excitation wavelength. Furthermore, each  microresonator can produce distinct emission peaks that serve as unique spectroscopic  “fingerprints” serving as photonic barcode. Unlike traditional quantum dot- or dye-doped  microresonators, a single WCPM microresonator can simultaneously generate both visible  (overt) and NIR (covert) photonic barcodes (Figure 1).  This dual-mode emission significantly  improves data encryption and enables versatile, doubly secured secure information encoding  that is invisible to the naked eyes. This unique photonic behavior, combined with the random  size distribution of the microbeads, generates complex and unpredictable spectral fingerprints,  making the resulting optical tags extremely difficult to replicate compared with conventional  fluorescent ink-based microcavities. Moreover, this WCPM-based system offers a rare-earth-  and metal-free platform that is scalable, reliable, and well-suited for next-generation anti- counterfeiting and photonic security applications.2\. Results and DiscussionThe white light emitting (WLE) carbonized polymer microspheres (WCPM) were synthesized  via hydrothermal techniques using citric acid (CA), natural peptide ε-poly-l-lysine (EPL), and  perylenetetracarboxylic dianhydride (PTCDA) in aqueous solution (Figure S1). The -COOH4groups from CA and -NH2 groups from natural peptides crosslinked to form spherical  architectures, resulting in light yellow-colored carbonized polymer microsphere (YCPM).\[10\]  Under UV excitation, YCPM exhibited strong cyan emission and emitted multicolor light  across the visible spectrum from cyan to red, depending on the excitation wavelength. To  enhance yellow and red-light emission more and extend emission further into the NIR region,  commercially available PTCDA dye molecules were introduced during synthesis. During the  reaction, PTCDA converted to perylenetetracarboxylic diimide (PTCDI), extending   conjugation through di- and trimerization processes, narrowing the band gap, enhancing NIR  absorbance and emission.\[44, 45\]Figure 2. (a-b) low to high magnified SEM images of the WCPM microbead. (c) EDS mapping  of single WCPM microbead.  (d and e) XRD and XPS survey spectra of WCPM. (f-h) De- convoluted HRXPS spectra of C, N, and O, respectively. (i) Magnified solid-state 13C CPMAS  NMR spectra of WCPM and compared with the EPL.Figure 2 a-b show the SEM images of WCPM and it shows the microbeads diameter range  from 5-15 μm and smooth surface similar to YCPM (Figure S2). The Energy-dispersive X-ray5spectroscopy (EDS) of a single microbead indicate that it is composed of mainly carbon (C),  oxygen (O), and nitrogen (N) (Figure 2c). Figure 2d shows X-ray diffraction (XRD) pattern  of the microbeads and shows a broad peak at 20 degree at 2 indicating the formation of  amorpous structures after the crosslinking reaction with EPL peptide. The X-ray photoelectron  (XPS) survey spectra, providing insights into elemental composition (Figure 2e). The XPS  survey spectra indicate that the surface atomic composition consists of approximately 68.8% C,  13.55 % N, and 17.65% O. The deconvoluted HRXPS spectrum of WCPM reveals various  functional groups. The C-1s spectrum shows three distinct peaks: C-C/C=C, C-N/C-O, and  COOH/CONH (Figure 2f).\[39, 46\] The N 1s spectrum features peaks at 399.0 eV (C-NH₂, C-N- C), 399.7 eV (amide), and 401.0 eV (amine/graphitic N), indicating precence of pyridinic and  graphitic nitrogen along with amide, and amine bonds (Figure 2g).\[46-48\] In the O 1s region,  peaks at 531.3 eV and 532.8 eV correspond to N-C=O and O-C=O bonds, confirming oxygen  functionalities in WCPM (Figure 2h). The solid-state nuclear magnetic resonance (ssNMR)  characterization using 13C revealed distinctive features in the magnified cross-polarization,  magic angle spinning (CPMAS) NMR spectra of pure EPL and WCPM (Figure 2i). In the 13C  CPMAS NMR spectra comparing WCPM to EPL raw materials, notable peaks appeared around  ≈29 and 40 ppm, corresponding to sp3-hybridized CH2 sequences in aliphatic carbons, which  differed from EPL.\[49\] Additionally, a broad peak at 173 ppm indicated a cross-linked structure  involving -COOH groups from CA and -NH2 groups from EPL, contributing to the formation  of WCPM structures (Figure S3). The broadening observed in the aliphatic carbon (CH₂)  spectral profile supports the of cross-linking between CA and EPL, while the upfield shifts of  the amorphous phase reflect conformational heterogeneity.\[50\] Additionally, new signals  appearing at 114 ppm suggest the presence of sp²-hybridized carbon atoms associated with  PAHs. A lower chemical shift at 88 ppm points to =CH carbons, potentially influenced by the  electron-withdrawing effects of two nitrogen atoms located at a two-bond distance from the  imide bond within PTCDI. Furthermore, the 13C CP-MAS NMR spectra reveal sharp peaks at  approximately 148 and 163 ppm, likely attributed to sp²-hybridized carbon atoms linked to  cyclic imide bonds originating from PTCDI.\[51\] The 15N CPM NMR also reveals a broad peak  at -263 ppm, indicative of the amide bonding configuration (Figure S4).\[52, 53\] These  characteristics indicated the conversion of PTCDI from PTCDA dye molecules, highlighting  the structural transformations observed in the WCPM material.6(g) (h)Figure 3. (a) UV-vis-NIR absorbance spectra comparing YCPM and WCPM. (b and c)  Comparative PL spectra and corresponding CIE diagram of WCPM and YCPM. (d and e)  Excitation wavelength-dependent PL spectra of YCPM and WCPM. (f) Photographs of WCPM  and YCPM under daylight and 365 nm UV light. (g) Schematic illustration of the in-situ  formation of PAHs from PTCDA within the WCPM matrix. (h) DFT calculation results for  PAHs model with increasing conjugation, showing computed energy diagrams of HOMO- LUMO energy gaps.Figure 3a shows a comparative analysis of the absorbance spectra of YCPM and WCPM across  the ultraviolet-visible to near-infrared (UV-VIS-NIR) wavelength range. The YCPM primarily  absorbs in the UV region, exhibiting distinct peaks at 280 nm and around 370 nm. These peaks  correspond to π–π\* and n–π\* electronic transitions associated with C–O and C–N bonding  structures, which originate from blue light-emitting molecular fluorophores formed inside the7microspheres. Additionally, a lower-energy absorption band is observed, attributed to n–π\*  transitions involving C=O and C=N bonds present in the cross-linked amide structures.\[54-56\] In  contrast, the WCPM exhibits new, strong absorption peaks at 500 and 536 nm, confirming the  incorporation of PTCDI fluorophores into the microstructures. Furthermore, additional weak  absorption bands extending into the red to NIR wavelength region are observed in the tail of  the spectrum compared with YCPM. Recent studies have reported that the formation of larger  PAHs through PTCDI-based di- and trimerization processes leads to VIS-NIR absorbance in  CD-based nanostructures.\[44, 45\] This extended π-conjugation in PTCDI-derived PAHs  contributes to the enhanced VIS-NIR absorbance and emission observed in WCPM compared  with YCPM. The UV-excited emission spectra of WCPM exhibit an extended emission range  from yellow to red wavelengths, leading to WLE, in contrast to YCPM (Figure 3b). Under UV  excitation, YCPM emits cyan light, while WCPM exhibits WLE, as confirmed by emission  spectra and the International Commission on Illumination (CIE) coordinates. The CIE  coordinate for WCPM is (0.30, 0.33), as shown in Figure3c corresponding to WLE. YCPM  shows excitation wavelength-dependent emission, where the intensity of visible light emission  at longer wavelengths gradually decreases as the excitation wavelength increases (Figure 3d).  The WCPM exhibits a broad emission under UV (360 nm) excitation compared to the YCPM,  resulting in single-component WLE (Figure 3e). Moreover, the WCPM also displays excitation  wavelength-dependent emission across the VIS-NIR region when the excitation wavelength is  varied (Figure S5). Interestingly, in the excitation range of approximately 470-500 nm, the  emission becomes excitation-independent, showing strong yellow and red emissions peaks at  551 nm, 588 nm, and 636 nm, respectively (Figure 3e and Figure S5). These spectral features  indicate the in situ chemical transformation of PTCDA into PTCDI-based molecular  fluorophore within the microspheres during their formation (Figure S6). Control experiments  revealed that the hydrothermal reaction between PTCDA and EPL led to the in-situ formation  of yellow-emissive PTCDI-based molecular fluorophores through chemical transformation.  These fluorophores exhibited broad absorption bands centered at 496 and 526 nm and displayed  excitation-independent yellow-to-red emission with characteristic peaks at 537, 577, and 629  nm under UV excitation (Figures S7).  The PL quantum yield (PLQY) of WCPM in the solid- state is approximately 30 % by 500 nm excitation (Figure S8) at solid state, whereas PTCDA  molecules alone exhibit emission with a PLQY \~ 3% at N-methyl-2-pyrrolidone (NMP)  solution and \< 1 % at solid state.\[57\] The fluorescence lifetime imaging microscopy (FLIM)  analysis of individual WCPM microbeads was performed under two different excitation  wavelengths (405 and 500 nm) from the same position (Figure S9). The results revealed8average decay times (av) of approximately 4.92 ns and 2.55 ns, respectively, with a narrow  lifetime distribution, indicating uniform optical characteristics of the microbeads.  The time- resolved photoluminescence (TRPL) spectra of PTCDI-EPL in the colloidal state exhibit τₐᵥ of  3.13 and 3.21 ns for the emission peaks at 540 nm and 580 nm, respectively, under 361 nm  laser excitation. Remarkably, these lifetimes increase to 30.4 and 20.4 ns in the WCPM system  (Figure S10). This significant enhancement can be attributed to the spatial confinement of  PTCDI-based fluorophores within the microcavity, which effectively suppresses aggregation- induced quenching and π-π energy transfer and promotes higher PLQY in the solid state.\[58\]  Due to the incorporation of PTCDI-based PAHs within the microbeads facilitates Förster  resonance energy transfer (FRET) due to their close packing, enabling efficient energy transfer  and resulting in the observed WLE in WCPM. The TRPL spectra of blue emission peak (\~454  nm), τav of YCPM decreases from 4.80 ns to 2.96 ns for the case WCPM, indicating \~ 38 % of  FRET energy transfer from YCPM based framework to PAHs during the UV light excitation  (Figure S11).\[33\] A digital photograph of YCPM and WCPM under daylight shows a noticeable  color shift, with YCPM appearing light yellow and WCPM appearing reddish color materials  and emit cyan and WLE under 365 nm UV excitation (Figure 3f). Figure 3g shows the  schematic representation of the formation of PTCDI-based PAHs. This process extends the - conjugation through dimerization and trimerization and confined inside the microstructures,  resulting in material with unique “chameleon-like” emission behavior from VIS-NIR  wavelength region by varying the excitation light source. To gain deeper insight into the optical  behavior, Density Functional Theory (DFT) calculations are being carried out on PAH  structures. These calculations include geometric optimization and energy level analysis,  revealing HOMO-LUMO energy gaps of 2.47 eV and 1.90 eV, respectively (Figure 3h). The  experimental and computational results clearly show a red shift in the absorbance spectra,  indicating that the WCPM can absorb light at longer wavelengths, from the visible to the NIR  region. This behavior comes from the formation of PTCDI-based fluorophores and extended  PAH structures inside the microbeads. These species act as light-emitting centers with different  energy gaps, leading to excitation wavelength-dependent PL across the VIS-NIR range. The  visible emission mainly originates from isolated PTCDI-like fluorophores, while the NIR  emission is produced by larger PAH networks with extended π-conjugation.9Figure 4. (a) Excitation wavelength-dependent μ-PL spectra from VIS-NIR wavelength from  a single microbead and corresponding -PL images excited with UV-VIS-NIR laser sources at  their center. (b) Schematic illustration of chameleon microcavity. (c) Wavelength adaptable  microresonator behavior of a microbead via changing the excitation laser source via excitation  at their right side and show the multicolor of WLE to deep red-NIR, and NIR emission (scale  bar 4 m).The -PL properties of individual microsphere were investigated by varying the excitation  wavelength across the UV-vis-NIR spectrum. When the same WCPM microbead was exciting  using different wavelengths (355, 470, 520, 570, 670, and 785 nm), a broad range of light10emissions was observed, spanning from the visible region to deep red (DR)-NIR and the NIR  wavelength range. Figure 4a shows the -PL spectra and images of the microbead when excited  at various laser wavelengths at their center. The corresponding -PL spectra demonstrates  wavelength-adaptable light emission from the visible to DR-NIR and the NIR region. The CIE  coordinates indicate that individual microbeads exhibit WLE under UV excitation, with the  color gradually changing from green to yellow, red, deep red (DR), DR-NIR, and NIR (Figure  S12). In contrast, the comparative -PL spectra of YCPM microbeads show orange emission  when excited with a 532 nm laser, with an emission center wavelength at 600 nm (Figure S13).  On the other hand, WCPM microbead displays three distinct emission centers at 545 nm, 590  nm, and 636 nm, attributed to the formation of PTCDI-based PAHs integrated into microbeads.  This -PL spectra of individual WCPM microbead exhibit color-adaptable emission from the  visible to NIR region, depending on the excitation wavelength, demonstrating a chameleon-like  fluorescence behavior (Figure 4b). Notably, when a single microbead (diameter \~ 12 m) is  excited at the edges, WGM-based light amplification is observed across the entire visible  spectrum (including white, green, yellow, red, and deep red-NIR) and into the NIR region. This  light amplification is achieved simply by changing the excitation laser wavelength, without  modifying the microcavity itself, solely changing its color flexibly like a chameleon (Figure  4c). Multiple microbeads (7.2 µm and 9.8 µm) exhibit chameleon-like microresonator  behaviors, where the WGM emission patterns are strongly dependent on the bead diameter  (Figure S14). In contrast, the YCPM microresonator's emission is restricted to the shorter  visible wavelength region (Figure S15). Surprisingly, unlike organic polymer-based  microresonators, the WCPM microbeads exhibit high stability against organic solvents, acid  treatments, and prolonged laser exposure (Figure S16). Overall, this eco-friendly, rare-earth- metal-free spherical microarchitecture, composed of a single material, exhibits color-adaptable  WGM-mode emission spanning the entire VIS-NIR spectral region. This performance  significantly surpasses that of previously reported spectral microresonators (Table S1), whose  emissions are typically limited by doped resonant PL enhancement due to WGM confinement  and confined to either the visible or NIR range. This chameleon-like microresonance, combined  with high stability, makes these materials highly promising for practical use in encrypted  photonic microbarcodes and secure authentication applications.11Figure 5. (a and b) Comparison of schematic illustration of visible microbarcodes generated by  conventional dye-doped microresonators versus visible and invisible microbarcodes by WGM- based microresonators. (c) Vis-NIR WGM-assisted microbarcode generation, along with  corresponding bright-field optical images and m-PL images obtained using 532 nm and 785 nm  laser excitation of same microresonators. (d) WGM emissions from individual WCPM  microbeads of varying sizes, along with their corresponding -PL images by 532 nm excitation  (scale bar 3 m). e) Correlation between λ2/Δλ and the d of microcavity. Correlation between  λ2/Δλ and the d of microcavity and corresponding linear fit to the function λ2/Δλ = neffπd  (redline).12Each synthesized microbead exhibits excitation-dependent emission spanning the visible to  NIR range when excited by lasers (Figure 4). This property enables the generation of both overt  (visible) and covert (invisible) microbarcodes using WGM resonance under different laser  excitations. The microbeads’ high sphericity, smooth surface, and high refractive index allow  efficient light confinement through total internal reflection, forming TE and TM optical modes.  These modes generate unique spectral barcodes, offering novel microscale optical tagging-in  contrast to conventional 1D barcodes, which require larger centimeter-scale dimensions.  Typically, conventional dye-doped (rhodamine 6G) polystyrene microresonators generate a  single microbarcode corresponding to the emission wavelength of the gain medium (Figure 5a  and Figure S17). In contrast, the WCPM exhibit multiple microbarcodes spanning both visible  and NIR regions (Figure 5b). This VIS-NIR emissive fingerprints allows them to function as  overt and covert barcodes for secure product tagging. Figure 5c shows the WGM emission in  the visible to the NIR wavelengths, as well as the corresponding photonic microbarcode patterns  obtained from the same single WCPM microbead when excited at 532 nm and 785 nm. The µ- PL images in both VIS and NIR wavelength regions show the bright ring patterns confirm light  confinement at their perimeter due to WGM resonance at both wavelength regions. This  approach enables the generation of dual VIS and invisible microbarcodes from individual  microbeads. The simplest expression for the WGM resonance positions is given by mλ = neffπd,  which corresponds to the first-order term of the asymptotic expansion of the Mie solution (Airy  function approximation),\[59, 60\] where m is an integer, λ the resonant wavelength, neff the  effective refractive index of the resonant mode, and d the microcavity diameter.\[27, 61, 62\] WGM  emission occurs when the optical path length matches an integer multiple of λ. Each microbead,  with its unique size and fixed refractive index, exhibits distinct sharp peaks, forming a spectral  fingerprint. This WGM-regulated emission spectrum enables the identification of microbeads,  that functioning similar to barcodes used for product recognition, making them ideal for  unclonable anti-counterfeiting applications. Figure 5d shows the optical modulation of WGM  resonance, where spectral variations correspond to differences in microbead size, along with  their respective μ-PL images under 532 nm laser excitation at the edges. The free spectral range  (FSR), defined as the wavelength difference between optical modes (TE/TM), is inversely  related to the microresonator diameter.\[30\] As the microcavity diameter increases from 7.3 µm  to 12.4 µm, the FSR gradually decreases from 10.6 nm to 6.1 nm. Figure 5e presents the linear  relationship between λ²/Δλ and d, with a fitted slope of neffπ = 4.75. Given π = 3.14, the effective  refractive index neff is determined to be 1.51. By varying the microcavity diameter, a wide range  of unique barcodes can be generated. Moreover, the coding capacity/security is significantly13enhanced by extending the emission spectrum from vis-NIR through excitation wavelength  tuning. This capability, which is not available in traditional dye-doped microcavities, allows for  more versatile and high-density encoding.Figure 6. (a,b) Experimental and simulated −PL spectra of an individual WCPM \~8.9 μm  microbeads excited at 532 and 785 nm. (c-d) Electromagnetic field distributions of TE and TM  resonances in the VIS and NIR wavelength region. Comparison of wavelength-adaptable  photonic barcodes for experiment (upper) and simulation (lower). (e) Comparison of visible  and invisible wavelength-adaptable photonic microbarcodes for experiment (upper) and  simulation (lower).14The -PL spectra across two distinct spectral regions, along with the corresponding field  profiles, were simulated using the finite-difference time-domain (FDTD) method.\[16\] The  emission from the WCPM was modeled as a dipole source placed near the edge of the sphere,  and the optical power was monitored via a transmission box enclosing the dipole. The power  obtained, normalized to the source power, represents the emission rate enhancement due to the  WGM resonance effect. The enhanced WGM emission spectra were then obtained by  multiplying this factor by the background emission.  The simulated WGM resonances in the  yellow red (visible) and wavelength regions, along with background emissions from 8.9-μm  WCPM microbeads, were analyzed under excitation with two different laser wavelengths. The  simulated spectra exhibit strong agreement with the experimentally measured emission spectra  obtained under 532 nm and 785 nm laser excitation (Figure 6 a, b). Here, the broad  fluorescence envelope corresponds to the background spectrum observed in the experiment  when the excitation spot was focused at the center of the sphere. These results confirm the  presence of both TE and TM modes within the WCPM microbeads due to the strong light  confinement. The variation in optical path lengths for TE and TM modes naturally leads to  differences in mode separation, resulting in nonuniform spectral spacing of the resonant peaks.  Note that the linewidth of the simulated peaks depends on the extinction coefficient k of the  WCPM. Accordingly, the k value was determined such that the linewidth in the simulation  matched that in the experiment, yielding k = 0.002. Figure 6c show the mode profiles at WGM  resonance peaks of 591.92 nm and 597.91 nm, showing the Hz field distribution for the TE  mode and the Ez  field distribution for the TM mode, respectively. These profiles highlight the  fundamental TE and TM mode characteristics with a radial mode number of 1. Similarly,  Figure 6d show the mode profiles at WGM resonance peaks in the NIR region (808.60 nm and  819.25 nm), represent the Hz field distribution for the TE mode and the Ez field distribution for  the TM mode. Both the experimental and simulated WGM emission patterns demonstrate the  potential for constructing photonic barcodes in the visible and NIR spectral regions (Figure 6e).  This tunability is achieved by simply varying the excitation wavelength from 532 nm to 785  nm, offering a powerful pathway for advanced photonic security and encryption applications.15Figure 7. (a and b) Schematic diagram of the potential application of WCPM based encrypted  photonics architecture with vis and NIR microbarcodes generation for secure product tagging  application. (c and d) Simple demonstration of VIS-NIR microbarcode generation from single  microbeads for authentication on a tagged bank card and resident card by varying the excitation  wavelength between 532 nm (VIS) and 785 nm (NIR).Figure 7a and b illustrate a proposed application of encrypted visible and invisible barcode  generation using these chameleon-like WCPM microcavities for product tagging and  authentication in information security. These microbeads are embedded within an identity card,  debit/credit card, serving as a unique identification tag that is nearly impossible to replicate due  to the distinct barcode patterns they produce. To verify authenticity, three tests are conducted16by varying the excitation source: UV light, a visible 532 nm laser, and an invisible 785 nm laser.  A single microbead generates corresponding barcodes in the visible and NIR regions, as shown  in Figure 7a. The recorded barcode data is securely uploaded to the cloud as a reference. For  authentication, an unknown identity card undergoes the same three tests. If the microbeads in  the card emit white light and generate the expected visible and NIR barcodes that match the  reference data, the card is confirmed as authentic. Otherwise, it is identified as counterfeit  (Figure 7b).  As a proof of concept, we have integrated WCPM microbeads into a used real  bank card and a used Japanese residence card (Figure 7c and d). In both cases, under UV  illumination, 532 nm and 785 nm laser excitation (Figure S18), the microbeads exhibit white  light emission and produced distinct visible and NIR spectral barcodes due to WGM,  confirming the authenticity of the cards. This microbead-based security system, capable of  generating both visible and invisible microbarcodes, significantly enhances security down to  the microscale region. It offers a promising and powerful approach for advanced anti- counterfeiting measures, addressing global security challenges.3\. ConclusionIn this work, we developed white-light-emitting carbonized polymer microsphere (WCPM)- based WGM microresonators, representing a significant advancement in photonic barcoding  for secure labeling and multilevel anti-counterfeiting applications. The WCPM design enables  a scalable, gram-scale, metal-free synthesis with strong PL, low toxicity, and excellent chemical  stability against acids and organic solvents, setting them apart from conventional polymer- or  oxide-based microcavities. The extended π-conjugation in WCPMs allows broadband emission  spanning the VIS-NIR region. Compared with traditional quantum dots and dye-doped  microresonators, WCPMs demonstrate superior spectral range, stability, and chemical  robustness. By utilizing the excitation-wavelength-dependent, color-variable emissions of the  microbeads, both visible (overt) and NIR (covert) microbarcodes can be generated, enabling  complex and tunable optical signatures for enhanced security. By incorporating these  microresonators into multilevel encrypted microbarcode systems, we establish a secure and  versatile anti-counterfeiting strategy. Encoding information across multiple spectral regions  adds an additional layer of encryption, making unauthorized replication highly challenging.  Overall, this work advances photonic security technologies and offers a practical, sustainable  platform for real-world applications.17Supporting InformationSupporting Information is available from the Wiley Online Library or from the author.AcknowledgementsThis work was financially supported by the JSPS-Kakenhi research grant (grant number  24K17589). BKB acknowledge The Japan Society for the Promotion of Science (JSPS) for the  JSPS postdoctoral fellowship. The authors also acknowledge Dr. Hiroyuki Yamada for  measuring the TRPL and Ms. Keiko Okano for technical assistance. Received: ((will be filled in by the editorial staff))  Revised: ((will be filled in by the editorial staff))  Published online: ((will be filled in by the editorial staff))References1\. 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Dynamic microbarcode shifts via excitation changes enhance encrypted optical  tagging and anti-counterfeiting, advancing photonic security with visible and invisible labeling  for next-generation secure authentication.Barun Kumar Barman\*, Keisuke Watanabe, Kenzo Deguchi, Shinobu Ohki, Kenjiro Hashi,  Atsushi Goto, Tadaaki Nagao \*Chameleonic Color-Variable Microbead Emitters for Multilevel Spectroscopic  Encryption from Visible to Infrared Wavelengths22