Localized electron states induced by various disorders, including defects and impurities,usually exist in solids. Their optical properties, especially their luminescence properties,are of both scientific and technological significance. But a microscopic theory has notyet been established for such localized-state ensemble (LSE) luminescence. In thisLetter, we attempt to fill this void via developing a quantum many-body (MB)luminescence theory taking into account both electron-phonon (e-p) and electronelectron(e-e) interactions. By using the developed MB-LSE theory, abnormal thermalbehaviors such as redshift and subsequent blueshift of peak position, narrowing andsucceeding broadening of linewidth, decline in intensity, and variation in lifetime canbe quantitatively interpreted. The roles of electron-phonon and electron-electroninteractions in the variable-temperature LSE luminescence are thus elucidated. Withinthe framework of the MB-LSE theory, moreover, Varshni’s empirical formula forbandgap temperature dependence and Huang-Rhys factor for e-p coupling are furtherderived and discussed.

To address the spectral deficiencies in the red region of commercial white LEDs, developing red-emitting phosphors with reduced dependence on rare-earth elements with limited availability is crucial for spectral compensation. Herein, microstructures and optical characteristics of Mn4+-activated Mg2GeO4 phosphors are presented. While the phosphor exhibits a single orthorhombic phase, its cryogenic micro-Raman and photoluminescence (PL) spectra comprises 19 peaks and three groups of vibronic emissions with wealthy fine structures, respectively. Following the split zero-phonon lines, nine pairs of vibronic lines with an energy separation of 3.5 meV are identified. Furthermore, the overall line shape of the three groups of phonon sidebands can be reproduced by the fully symmetric electron-phonon coupling model, enabling determination of the total density of phonon states. The study sheds light on complicated luminescence fine structures in Mn4+-activated oxide phosphors, offering valuable insights into the design of red-emitting phosphors.

Engineering the coupling between host-lattice phonons and doped Cr3+ ions is pivotal for regulating optical properties of broadband near-infrared (NIR) phosphorsand prompting their applications. Here, we investigate Ca2Ga0.99- xInxNbO6:0.01Cr3+ (x = 0-0.99) phosphors to elucidate how Ga/In substitution-induced B-site disorder tunes the crystal structure, vibrational modes, Cr3+ excited bands, and excitation-relaxation dynamics. A gradual evolution from an ordered framework to a disordered one is revealed through XRD, Raman, and 71Ga ssNMR measurements, resulting in symmetry breaking and activation of low-frequency phonons. The PLE spectra demonstrate composition-driven tuning of the host-Cr3+ hybridized excited bands, yielding two dominant peaks at similar to 385 and 460 nm for x = 0.495, which match well with commercial UV and blue LEDs emissions, enabling dual-mode excitation. Huang-Rhys factor S approximate to 3.8 for ion-lattice coupling and Dq/B approximate to 2.05 for crystal field effect are determined by fitting the phonon sidebands using the multimode Brownian oscillator model and Tanabe-Sugano model analysis. It is further shown that increasing In3+ content strengthens phonon-assisted nonradiative relaxation within the split 4T2 (4F) manifold, thereby resulting in thermal redistribution of luminescence intensity and shortened lifetimes. Overall, adjusting B-site disorder provides an effective handle to engineer impurity-host interactions and tailor the performance of Cr3+-activated NIR phosphors.

Ce3+-doped garnet transparent ceramics provide an ideal model system for elucidating the coupling between lattice structure, crystal-field strength, and thermal luminescence dynamics in solid-state emitters. Here, a comparative study of Y3Al5O12:Ce (YAG:Ce) and Lu3Al5O12:Ce (LuAG:Ce) transparent ceramics reveals how lattice contraction and crystal-field modulation govern their excitation-dependent behavior. Rietveld refinement and high-resolution microscopy confirm that replacing Y3+ with smaller Lu-3(+) induces lattice compression and local structural distortion, strengthening the crystal field around Ce-3(+) ions. Both ceramics exhibit high transparency (>80% at 600 nm), near-unity internal quantum yields (98.35% for YAG:Ce, 99.52% for LuAG:Ce), and nanosecond-scale lifetimes (100.7 ns vs. 86.9 ns). Temperature-dependent excitation spectroscopy uncovers contrasting trends: the ultraviolet excitation band of YAG:Ce undergoes a red-shift and intensity quenching with increasing temperature, whereas that of LuAG:Ce remains nearly invariant and even intensifies. Low-temperature deconvolution identifies reduced Huang-Rhys factors and weaker phonon coupling in LuAG:Ce, accounting for its superior thermal stability. When integrated into LED devices, LuAG:Ce delivers a luminous efficacy of 117 lm/W at the driving electrical power of 5.74 W, demonstrating outstanding color and thermal robustness. These findings establish a direct structure-field-luminescence relationship, offering fundamental guidance for designing thermally resilient, high-power optical materials.

Transition-metal activators such as Cr3+ offer an exceptional platform for probing the interplay between crystal structure and electronic transitions in solid-state luminescent materials. Here, a composition-controlled La3Sc2Ga3O12: Cr system is demonstrated that undergoes a reversible transformation from a garnet (Ia d) to a perovskite (Pm m) structure through progressive Al3+ substitution. The resulting lattice contraction strengthens the octahedral crystal field around Cr3+, driving a transition from broadband near-infrared (NIR) emission (800 nm, 4T2 -> 4A2) to narrowband deep-red luminescence (731 nm, 2E -> 4A2). Structural refinements and spectroscopic analyses reveal a field-induced crossover between spin-allowed and spin-forbidden transitions, accompanied by suppressed electron-phonon coupling and a lifetime extension from microseconds to milliseconds. The configurational-coordinate model further links lattice vibrations to emission dynamics. Beyond mechanistic insight, the broadband NIR emitter enables nondestructive imaging, whereas the deep-red perovskite matches phytochrome absorption for plant photoregulation. This study establishes a unified structure-field-emission relationship and presents a general strategy for tuning broadband-to-narrowband transitions in transition-metal-activated oxides via crystal-field modulation.

The substrate‐free ultrathin phosphor‐glass composite (PGC) provides significant advantages for all‐inorganic light‐emitting diodes (LEDs), offering enhanced resistance to light radiation and chemical corrosion. However, achieving a PGC thickness below 100 µm remains challenging due to its brittle nature. Herein, this work presents a novel strategy to fabricate an ultrathin cyan PGC for all‐inorganic LEDs, based on our home‐synthesized Ce‐activated Ca 2 YAlGa 2 Si 2 O 12 phosphor (CYAGS:Ce). The phosphor emits bright cyan light centered at λ em 497 nm with a FWHM of 93 nm and an internal quantum yield (IQY) greater than 60%. The luminescence mechanism, including concentration and thermal quenching, is investigated in detail. Using tape‐casting and low‐temperature co‐firing, an ultrathin PGC with a thickness of 98 µm is achieved. Structural and luminescence properties are compared to highlight the glass matrix's influence. Furthermore, based on as‐prepared ultrathin PGCs, a compact LEDs with a low correlated color temperature (CCT, 3384 K) and high color‐rendering index (CRI, R a = 85.7) is obtained by integrating both red and cyan PGCs with a commercial 420 nm blue chip. This work advances the understanding of CYAGS:Ce cyan phosphor and provides a versatile strategy for fabricating ultrathin PGCs, highlighting their potential applications in all‐inorganic LED lighting.

Large-size ultrathin phosphor-glass composites (PGCs), characterized by superior thermal dissipation properties, have demonstrated considerable potential for high-power illumination and adjustable color emission. Here, a facile and versatile strategy is presented to fabricate highly efficient ultrathin PGCs with dimensions reaching 1044 x 45 x 0.1 mm3, using an integrated tape-casting and low-temperature co-firing approach. Phosphor particles are embedded into the glass matrix via a pressureless sintering process. The impact of the glass matrix on the luminescent properties of both yellow and red phosphors is systematically evaluated. These findings indicate that ultrathin PGCs embedded with YAG:Ce particles exhibit an exceptionally high photoluminescence quantum yield (PLQY) of 98.6%, while those incorporating CaAlSiN3:Eu2(+) phosphors achieve a PLQY of approximate to 93.4%. Additionally, comprehensive analyses are conducted on spectral blue shifts, luminescence lifetime variations, and temperature-dependent photoluminescence characteristics over a broad temperature range. Light-emitting diode (LED) devices fabricated using these ultrathin PGCs show superior luminous performance, notably exhibiting a high electrical power threshold prior to luminescence saturation. Furthermore, it is successfully demonstrated tunable color emission in these ultrathin PGCs by varying the weight ratios of different phosphors. These remarkable ultrathin PGCs represent a significant advancement, providing promising and highly efficient solutions for next-generation high-power commercial LED illumination applications.

Mn4+-doped fluoride phosphors represent a significant class of narrow band red-emitting materials, whose luminescent properties are profoundly influenced by electron-phonon coupling. However, the parity-forbidden nature of these electronic transition systems is incompatible with the conventional Condon approximation, which is widely adopted in the classic theories such as the Huang-Rhys theory, a framework established on the assumption of parity-allowed electric dipole transitions. This results in a critical knowledge gap regarding the principles governing the phonon sidebands of parity-forbidden electronic transitions. This study experimentally reveals a pronounced parity-dependent intensity distribution in the phonon sidebands of these systems: significantly suppressed even-order sidebands and normally observed odd-order sidebands. To elucidate the phenomenon, we extend the Huang-Rhys theory to parity-forbidden systems by incorporating the Herzberg-Teller approximation into the treatment of the transition matrix elements. The improved theory successfully uncovers the physical mechanism behind the strong suppression of the even-order sidebands in the parity-forbidden systems, in which the Huang-Rhys factor is derived as S=((2I_3)/(9I_1 ))^(1/2). This work not only reveals new findings regarding the phonon sidebands of the parity-forbidden electronic transition systems, but also establishes an improved theoretical framework for understanding the electron-phonon coupling mechanisms of color centers in solids.

This study investigates the variable-temperature R-lines luminescence spectra of Cr3+ ions in a composite solid comprising alpha-Al2O3 and borate fluorescent glass. A divergence in the thermal broadening (Delta Gamma) of the R1 and R2 lines is observed at temperatures above 140 K. The experimental data were analyzed using McCumber-Sturge theory, incorporating the significant effects of acoustic phonon scattering on the effective Debye temperatures. The thermal broadening of both R-lines was found to strongly depend on excitation energy over a broad range. Furthermore, the excitations at the low-energy side of 4A2 -> 4T2 band exhibited pronounced negative thermal quenching behaviors in both R-lines. These findings provide new insights into the complex many-body interactions underlying the luminescence of functional ions in solids and offer promising opportunities for regulating the thermal behavior of Cr3+ ions' R-lines.

Here we investigate the temperature-dependent non-Markovian dynamics of the SiV^- center in diamond, focusing on the roles of low- and high-frequency quasi-localized phonon modes. Low-frequency phonons exhibit stronger electron-phonon coupling, leading to long-lived dephasing rate, while high-frequency phonons induce rapid attenuation of oscillatory dephasing rate facilitating a persistent memory effect. The non-Markovianity measure N_C shows memory effects persisting at low temperatures but diminishing at high temperatures due to enhanced damping. The temperature dependence of N_C follows a monotonic decay, from which a transition temperature T_NM=110 K is determined. These results highlight the interplay between phonon activation and damping in shaping quantum coherence, offering insights for optimizing solid-state quantum systems.

Carrier localization in semiconductor materials often arises from band fluctuations, causing energy minima that trap carriers. The anomalous luminescence behaviors of localized states in such materials are complex to investigate quantitatively. In this paper, we propose a novel and accessible method for analyzing the temperature dependence of localized-state luminescence by modifying the localized-state ensemble model. The thermal carrier redistribution effect on the temperature-dependent luminescence peak position is explained by a small energy shift near the density of states center of localized states, yielding a simple and physically intuitive expression. This method accurately reproduces the “S-shaped” temperature dependence of the luminescence peak position. Its validity is confirmed by fitting various systems, demonstrating good consistency with the previous models. Additionally, analytical formulas for the changes of entropy and enthalpy in the localized systems are derived, revealing that entropy and enthalpy peak at intermediate temperatures due to the carrier redistribution and delocalization effects. This thermodynamic analysis offers deeper insights into the microscopic properties of localized states. The modified model will provide a more accessible framework for the quantitative study of the thermodynamics of localized-state luminescence in disordered materials.

Distinctive valley structures of the energy band in two-dimensional (2D) transition metal dichalcogenides (TMDs) offer various potential momentum-forbidden dark excitons, which significantly alter the decoherence of bright direct KK excitons, mainly via phonon-assisted intervalley scatterings. Nevertheless, the energy position influence of the intervalley dark excitons on the bright exciton decoherence has been rarely investigated. Herein, we report on a systematic combined study of optical spectroscopic experiments and quantum theory calculations for demonstrating the subject. At room temperature, external biaxial strain was applied to mono-, bi-, and trilayer WS2 flakes; meanwhile, reflectance spectra were measured, followed by a quantum Rabi theory calculation to determine the homogeneous line widths of the bright KK excitons. It is unraveled that the homogeneous broadenings of all three flakes show non-monotonic dependence on strain: Decrease first and then turn to increase. Furthermore, the turning strain becomes larger for the thicker flakes. In order to quantitatively interpret the phenomenon, various individual contributions to the homogeneous broadening were calculated with the variational Ansatz, exhibiting an almost linear relationship with external strain. In particular, the energy positions of the intervalley dark excitons were revealed as an important factor tuning the bright excitonic decoherence. Enhancement coefficients of the ΓK, KΛ, and KΛ' intervalley scatterings, namely, ξΓK, ξKΛ, and ξKΛ', were thus defined and inferred to be approximately -0.1, -0.34, and -0.4, respectively. These findings demonstrate the important roles of the intervalley dark exciton energy positions in bright exciton decoherence, offering insights into the many-body physics in 2D semiconductor systems.

Herein, we present an experimental demonstration of the robust exciton-trion polaritons (ETPs) by measuring and simulating the resonance reflectance spectra of various configurational WS2 monolayers with different dielectric screenings. Moreover, the oscillator strength and decoherent behavior of such hybrid ETPs can be tuned via utilizing dielectric screening effect. The effect is attributed to the regulation of the Coulomb coupling between excitons and trions by changing the surrounding dielectric constant. The demonstration and tunability of the robust ETPs offers a novel pathway for researching novel phases of quantum matter in a quantum many-body physics regime.

Understanding the effects of atomic defects on the optical functionality of two-dimensional (2D) layered materials is critical to develop novel optical and optoelectronic applications of these ultimate materials. Herein, we correlate sulfur vacancies (VS) and luminescence properties of dark trions in monolayer WS2 through introducing VS defects and conducting a systematic optical spectroscopic characterization at cryogenic and room temperatures. It is unraveled that the VS defects can brighten the dark trions via introducing a stronger spin-orbit coupling due to the space inversion symmetry broken by the defects. Furthermore, the wavefunction localization of the dark trions bound at VS defects results in significant enhancement of the phonon scattering from the K2 valley phonons and hence makes the K2 phonon replica dominant in the emission spectrum. Theoretical calculations of the temperature-dependent photoluminescence spectra with quantum mechanics-based multimode Brownian oscillator model show strong support for the above arguments. Brightening the dark excitons not only sheds light on the understanding of the intriguing excitonic properties of 2D semiconductors, but also may open a way for regulating the optoelectronic performance of two-dimensional semiconductors.

Ultrafast conversion dynamics between the NV0 and NV- charge states in diamond is crucial for spin-state manipulation and readout. However, the underlying mechanism of the conversion, including the effective excitation wavelength, the time scales of the conversion, and the influencing factors, is still unclear. Here, we proposed a method to probe the ultrafast conversion of the two charge states via two-photon excitation with femtosecond laser pulses separated by 12.5 ns. We found that the highest conversion efficiency occurs at the excitation wavelength of around 532 nm, and the efficiency increases with temperature as well. The conversion time from NV0 to NV- is obtained to be around 75 ps at 300 K. These findings advance the understanding of NV center charge-state dynamics and provide insights for high-speed spin readout in quantum information applications.

Luminescence from high-lying excited states, such as the 2G9/2 level of Er3+, has been rarely explored due to its low population and complex excitation mechanisms. However, such luminescence carries important information of high-lying excited states, and hence offers a unique probe for understanding temperature-driven dynamics and phonon-mediated processes in luminescence upconversion systems. Herein, we report temperature-dependent upconversion photoluminescence measurements of Er3+ in Er3+-Yb3+ co-doped transparent ceramics, with a particular focus on transitions involving closely spaced Stark-split sub-levels in the violet emission band. Two excitation pathways are employed to investigate the thermal behavior mediated by phonons. The observed negative thermal quenching phenomenon under 980 nm excitation is well described through a rate-equation-based model that includes thermally coupled Stark sub-levels, phonon-assisted optical excitations and multi-phonon nonradiative relaxation. These insights into the phonon-assisted population dynamics provide a physical basis for the future development of optical thermometric applications.

The performance enhancement of MXene/semiconductor heterostructure-based light detectors is greatly restricted by the relatively small junction barrier due to the limited work function of MXenes. The work function of MXenes can be largely adjusted to approach 600 meV through simple incorporation of V2O5 via a charge transfer doping mechanism. Exploiting this strategy, the performance of MXene/GaN heterostructure-based deep ultraviolet (DUV) photodetectors has been greatly improved. Specifically, the photocurrent is enhanced by nearly 3 times, and the dark current is suppressed at the lowest order of magnitude, resulting in improved responsivity and specific detectivity of 121.6 mA/W and 2.23×1013 Jones, respectively, at 265 nm. The device also displays an ultralow dark current of 10−14 A, a fast response speed of 0.4 ms/15.1 ms, a large linear dynamic range exceeding 150 dB, and a high DUV/near ultraviolet rejection ratio of 2.41×105. Owing to its good device performance, the detector is capable of sensing weak photon signals produced by a fire flame and functions as an optical receiver to transmit a text signal in a DUV light communication system. The proposed MXene doping method is expected to help develop MXene-based electronic/optoelectronic devices, and the present DUV photodetectors will find potential applications in DUV optoelectronic systems.

Conventional pulsed Nd-doped solid-state lasers (SSLs) typically employ broadband white-light lamps as the primary pump source, enabling the generation of high-energy laser outputs up to hundreds of joules. However, the limited spectral overlap between the visible-light emission and the absorption bands of Nd3+ ions hinders further system simplification and cost reduction. In this work, we present a spectrally matched phosphor, La3Sc2Ga3O12:Cr3+ (LSGG:Cr3+), which exhibits exceptional spectral alignment with the YAG:Nd3+ absorption band, facilitating efficient blue-to-near-infrared (NIR) optical down-conversion for resonant pumping of Nd3(+) ions. Spectroscopic analyses identify an optimal Cr3+ doping concentration of 1 at.% and a phonon coupling energy of 21 meV, contributing to the phosphor's high internal quantum yield (>78%) and ensuring efficient optical conversion. To address thermal challenges, we developed a novel ultrathin (105 mu m) phosphor-glass composite (PGC), which demonstrates superior thermal stability and maintains luminescent dynamics. When integrated with a broadband light source, the LSGG:Cr3+-based PGC converts poorly absorbed visible light into highly absorbable NIR light for Nd3+ ions, serving as an effective nonlinear spectral converter. This study establishes a promising energy-saving approach for broadband-pumped SSLs through advanced luminescent spectral engineering.

Efficient anti-Stokes vibronic luminescence (ASVL) in solids is of both scientific and technological interest. However, it is challenging to achieve an efficient ASVL in solids under the excitation of incoherent, weak light. In this article, we present an experimental demonstration of a pronounced ASVL in Mn4+-activated K2SiF6 microcrystal phosphor under the excitation of microwatt continuous-wave incoherent light at room temperature. Meanwhile, a clear phonon resonance enhancement effect is demonstrated in the ASVL luminescence. These findings demonstrate the advantages of the efficient ASVL in solids compared with the conventional two-photon upconversion luminescence.