Bandgap Tailoring via Si Doping in Inverse-Garnet Mg3Y2Ge3O12:Ce(3+) Persistent Phosphor Potentially Applicable in AC-LED

High-Performance Tunable Near-Infrared Emitters of Cr3+-Activated Garnet Phosphor Enabled by Chemical Unit Co-Substitution

The escalating demand for portable near-infrared (NIR) light sources has posed a formidable challenge to the development of NIR phosphors characterized by high efficiency and exceptional thermal stability. Taking inspiration from the chemical unit co-substitution strategy, high-performance tunable (Lu3- xCax)(Ga5- xGex)O12:6%Cr3+ (x = 0-3) phosphors are designed with an emission center from 704 to 780 nm and a broadest full width at half maximum (FWHM) of up to 172 nm by introducing Ca2+ and Ge4+ ions into the garnet structure. In particular, Lu3Ga5O12:6%Cr3+ demonstrates an anti-thermal quenching phenomenon (I423K = 113.1%). Compared to Lu3Ga5O12:6%Cr3+, Lu2CaGa4GeO12:6%Cr3+ exhibits significantly improved FWHM and IQE by 108 nm and 25.5%, respectively, while maintaining good thermal stability (I423K = 80.4%). Finally, Lu2CaGa4GeO12:6%Cr3+ phosphor is combined with a 465 nm blue LED chip to fabricate NIR LED devices, exhibiting a NIR electroluminescence efficiency of 13.31%@100 mA and demonstrating successful applications in nocturnal illumination and biomedical imaging technology. This work offers a fresh perspective on the design of highly efficient NIR garnet phosphors.

Rh(iii)-catalyzed building up of used heterocyclic cations: facile access to white-light-emitting materials

The first example of rhodium-catalyzed nondirected C-H activation/annulation reactions for the construction of fused heterocyclic cations is reported herein with excellent regioselectivity. Deuterium-labeling experiments indicated that the C(sp3)-H bond cleavage of the N-methyl group might be the rate-limiting step during the reaction process. This protocol provides an opportunity to rapidly access highly π-conjugated fused heterocyclic cations, which opens up a new avenue for efficient screening of single-molecular white-light-emitting materials, pure red-light-emitting materials, and π-conjugated radical materials. Importantly, novel white-light-emitting materials exhibited distinct anti-Kasha dual-emission and could rapidly be fabricated into robust organic and low-cost white light-emitting diodes.

Adjusting luminescence properties of ZnAl2O4:Mn2+(Mn4+), Li+ phosphors through cation substitution

ZnAl2O4 with a typical spinel structure is highly expected to be a novel rare-earth-free ion-activated oxide phosphor with red emission, which holds high actual meaning for advancing phosphor-converted light-emitting diode (pc-LED) lighting. Among the rare-earth-free activators, Mn4+ ions have emerged as one of the most promising activators. Considering the price advantage of MnCO3 generating Mn2+ ions and the charge compensation effect potentially obtaining Mn4+ ions from Mn2+ ions, this research delves into a collection of ZnAl2O4:Mn2+(Mn4+), x Li+ (x = 0%-40%) phosphors with Li+ as co-dopant and MnCO3 as Mn2+ dopant source prepared by a high temperature solid-state reaction method. The lattice structure was investigated using X-ray diffraction (XRD), photoluminescence (PL), and photoluminescence excitation (PLE) spectroscopy. Results suggest a relatively high probability of Li+ ions occupying Zn2+ lattice sites. Furthermore, Li+ ion doping was assuredly found to facilitate the oxidization of Mn2+ to Mn4+, leading to a shift of luminescence peak from 516 to 656 nm. An intriguing phenomenon that the emission color changed with the Li+ doping content was also observed. Meanwhile, the luminescence intensity and quantum yield (QY) at different temperatures, as well as the relevant thermal quenching mechanism, were determined and elucidated detailedly.

The effects of Lu3+, Gd3+ and Ga3+ substitution on the photoluminescence of Y2.95-x-yLuxGdyAlzGa5-zO12:0.05Ce3+ phosphors for high-power white AC-LEDs

Various yellowish-green persistent phosphors of Y2.95-x-yLuxGdyAl5-zGazO12:0.05Ce3+ (x = 0-1, y = 0-1, z = 1-4) were successfully synthesized by the one-step high-temperature solid-state reaction method in air. The effects of simultaneous doping of Lu3+, Gd3+ and Ga3+ on the luminescence properties of the phosphors were investigated in detail for the first time. Herein, the microstructure, morphology, afterglow performance, luminescence properties, thermoluminescence, thermal quenching and flicker index of the efficient blue-light-activated Y2.95-x-yLuxGdyAl5-zGazO12:0.05Ce3+ phosphors were tested. The τ90 and τ80 values of Y1.45LuGd0.5Al2.5Ga2.5O12:0.05Ce3+ are 10.8 ms and 33.2 ms, respectively. These parameters are important in terms of effectiveness in reducing flicker in alternating current (AC) LEDs. Compared with the conventional Y3Al2Ga3O12:Ce3+ phosphor, the Y1.45LuGd0.5Al2.5Ga2.5O12:0.05Ce3+ phosphor has a better luminescence performance, stronger afterglow performance, and lower flicker index. The quantum yield of the Y1.45LuGd0.5Al2.5Ga2.5O12:0.05Ce3+ phosphor was 86.42% and the luminous efficiency of the LED devices prepared with it reached 92.12 lm W-1 when operated at 100 mA. Integrating sphere and spectroradiometer tests as well as CIE chromaticity diagrams indicate that the AC-WLEDs assembled by mixing the Y1.45LuGd0.5Al2.5Ga2.5O12:0.05Ce3+ phosphor and a commercial red phosphor in an appropriate ratio could obtain ideal white light with a high color-rendering index (87.9) and the flickering index was successfully reduced from 100% to 61.4%.

Ce3+-Doped Li2Ca5Gd(BO3)5 Phosphors with Multiple Luminescent Centers and High Pressure Sensitivity under Near UV Excitation

The performance of Ce3+-based phosphors under mechanical high pressures becomes attractive due to the potential application as a visual pressure sensor. Li2Ca5Gd(BO3)5 was selected as the host for the Ce3+ doping. Rietveld refinements reveal that rare earth cations occupy M1, M2, and M3 sites, and indeed, the photoluminescent spectra of Li2Ca5Gd1-xCex(BO3)5 (0.005 ≤ x ≤ 0.15) exhibit the characteristic of multiple activators, defined as CeI, CeII, and CeIII, with the maximal emission wavelength at ∼444, 419, and 378 nm, respectively. The optimal internal and external quantum efficiencies are 86.29% for x = 0.005 and 20.26% for x = 0.10, respectively, under the NUV excitation at 363 nm. In-situ high pressure emission spectra under 375 nm excitation exhibit an overall red-shift, and the linear pressure susceptibilities up to 6.7 GPa for CeI and CeII centers are -390 and -279 cm-1/GPa, respectively, which is probably the largest among Ce3+-doped oxides and oxysalts. Due to the above superiorities, Ce3+-doped LCGB possesses a high potential as a visual pressure sensor, and this is a successful study on the structure-property relationship of inorganic materials.

Persistent luminescent nanophosphors for applications in cancer theranostics, biomedical, imaging and security

The extraordinary and unique properties of persistent luminescent (PerLum) nanostructures like storage of charge carriers, extended afterglow, and some other fascinating characteristics like no need for in-situ excitation, and rechargeable luminescence make such materials a primary candidate in the fields of bio-imaging and therapeutics. Apart from this, due to their extraordinary properties they have also found their place in the fields of anti-counterfeiting, latent fingerprinting (LPF), luminescent markings, photocatalysis, solid-state lighting devices, glow-in-dark toys, etc. Over the past few years, persistent luminescent nanoparticles (PLNPs) have been extensively used for targeted drug delivery, bio-imaging guided photodynamic and photo-thermal therapy, biosensing for cancer detection and subsequent treatment, latent fingerprinting, and anti-counterfeiting owing to their enhanced charge storage ability, in-vitro excitation, increased duration of time between excitation and emission, low tissue absorption, high signal-to-noise ratio, etc. In this review, we have focused on most of the key aspects related to PLNPs, including the different mechanisms leading to such phenomena, key fabrication techniques, properties of hosts and different activators, emission, and excitation characteristics, and important properties of trap states. This review article focuses on recent advances in cancer theranostics with the help of PLNPs. Recent advances in using PLNPs for anti-counterfeiting and latent fingerprinting are also discussed in this review.

Tetracoordinate Fe3+ Activated Li2ZnAO4 (A = Si, Ge) Near-Infrared Luminescent Phosphors

Fe3+-doped near-infrared (NIR) phosphors have received a lot of interest because they are nontoxic, inexpensive, and ecologically benign. In this work, Fe3+-activated Li2ZnAO4 (A = Si, Ge) phosphors were synthesized by solid-phase reactions, in which Fe3+ entered the Zn2+ tetrahedral site. When excited by 300 nm UV light, broad NIR emission bands at 750 nm (Li2ZnSiO4: Fe3+) and 777 nm (Li2ZnGeO4: Fe3+) were observed, with internal quantum efficiencies (IQE) of 62.70% (Li2ZnSiO4: Fe3+) and 30.57% (Li2ZnGeO4: Fe3+). The thermal stability was increased from 35.43 to 49.79% at 373 K via cationic regulation. The combination of activation energy, electron-phonon coupling, and Debye temperature explained the improved thermal stability of Li2ZnGeO4: Fe3+ phosphor. Besides, the as-synthesized phosphor demonstrated sensitive and selective Cu2+ ion detection.

Mechanoluminescence Affected by Trap Types and Excitation State Positions in Mg3Ca3(PO4)4:Eu2+/Mn2+/Ce3+ for Multimode Anticounterfeiting

Mechanoluminescence (ML) materials with tunable emissions can serve in many practical applications; however, their underlying mechanism still needs further clarification. Herein, we developed Eu²⁺-/Mn²⁺-/Ce³⁺-activated Mg₃Ca₃(PO₄)₄ (MCP) phosphors and studied their luminescence properties by device fabrication. The intense blue ML is obtained by fabricating MCP:Eu²⁺ into the polydimethylsiloxane elastomer matrix. The red ML of relatively weak intensity is received in Mn²⁺ activator, but the ML for the Ce³⁺ dopant is nearly quenched in the same host. The possible reason is proposed from the analysis of the relative positions between the excitation state and conduction band, together with the trap types. The appropriate location of the excited energy levels in the band gap allows for a larger probability of efficient ML when shallow traps near the excitation states are created synchronously as an effective energy transfer (ET) channel. The concentration-dependent ML for the MCP:Eu²⁺,Mn²⁺-based devices indicates that the emitting light color can be tailored, where several ET processes among oxygen vacancies, Eu²⁺, Ce³⁺, and Mn²⁺, occur. The luminescence manipulation with dopants and excitation sources demonstrates the potential applications in visualized multimode anticounterfeiting. These findings open up many possibilities for constructing new ML materials by introducing appropriate traps into the band structures.

Ultra-Broadband Near-Infrared Phosphors Realized by the Heterovalent Substitution Strategy

Near-infrared (NIR) phosphor-converted light-emitting diodes with broadband emission have received considerable interest. However, there remains a challenge in the construction of ultra-broadband NIR phosphors, hindering their further application. In this work, a heterovalent substitution strategy is proposed to construct a novel ultra-broadband NIR-emitting LaTiTaO₆:Cr³⁺ phosphor with a full width at half maximum of ∼300 nm. Crystal structure, time-resolved emission spectroscopy, and electron paramagnetic resonance analyses confirm that only one crystallographic site of Cr³⁺ with separated ions exists. Electron and phonon coupling (EPC) evaluated by the Huang-Rhys factor (S) reveals that the heterovalent substitution strategy contributes to strong EPC with S = 9.185, resulting in ultra-broadband emission. Interestingly, a remarkable blue shift of emission from 1050 to 922 nm with increasing temperature is observed. Moreover, the application of LaTiTaO₆:Cr³⁺ phosphor is demonstrated in the qualitative analysis of ethanol/water mixtures. The work will enrich the toolbox for designing broadband NIR-emitting materials.

Affordable phosphor-converted LEDs with specific light quality facilitate the tobacco seedling growth with low energy consumption in Industrial Seedling Raising

Industrial Seedling Raising (ISR) is increasingly becoming an important part of Modern Agriculture because of its efficient utilization of land, water, and fertilizer as well as its advantages of being not easily affected by the weather. However, the high cost and high energy consumption of light sources for plant growth is limiting the popularization of ISR technology. Phosphor-converted light-emitting diodes (pc-LEDs) make use of relatively affordable red phosphor and blue light chips, providing an adjustable spectrum to optimize plant growth. To identify the energy-saving light quality of pc-LEDs, we investigated the effects of a variety of light qualities on the growth of tobacco seedlings. Y₃Al₅O₁₂:Ce³⁺, CaAlSiN₃:Eu²⁺, KAl₁₁O₁₇:Eu²⁺ phosphors were combined with the blue light chip according to different proportions to produce the following light sources: CK (white light), T1 (blue light), T2 (red light), T3 (red: blue light ratio = 1:4), T4 (red: blue light ratio = 4:1). The tobacco variety Xiangyan7 grown continuously under T1, T2, T3, and T4 significantly increased the leaf area, stem length, biomass, root area and main root length compared with those grown under white light. Among the five kinds of light qualities tested, T4 treatment exerted the best effect on leaf development and biomass increase, while T2 exerted the best effect on stem elongation. The cytological analysis demonstrated that the promotion of the cell size and cell number of leaf epidermal cells by T1-T4 might contribute to the leaf expansion. Further analysis at the molecular level suggested that the light quality affected the RNA levels of the genes involved in cell division and expansion. When tobacco seedlings reached the same biomass, T1-T4 light sources saved 71%, 86%, 80% and 89% of electric energy respectively compared with white light. Therefore, the application of specific pc-LEDs not only reduces the cost of light source production, but also saves energy consumption, offering great potential for ISR technology to cut costs and increase efficiency.

Enhanced blue-light excited cyan-emitting persistent luminescence of BaLu2Al2Ga2SiO12:Ce3+, Bi3+ phosphors for AC-LEDs via defect modulation

Alternating current light-emitting diodes (AC-LEDs) have received significant attention from both academia and industry due to their remarkable benefits of more compact volume, cheaper manufacturing cost, greater energy usage efficiency, and longer service life. One of the most significant challenges for AC-LEDs is the flicker effect, which is mainly caused by the unavoidable 5-20 ms dimming time. Aiming to reduce the flicker effect, we designed a series of excellent blue-light excited cyan-emitting persistent luminescence (PersL) phosphors BaLu₂Al₂Ga₂SiO₁₂:Ce³⁺, Bi³⁺ via defect engineering of co-doping Bi³⁺. Interestingly, we found that co-doping Bi³⁺ not only effectively enhanced the PersL intensity, but also regulated the PersL lifetime of this phosphors. As the Bi³⁺ co-doping concentration increases to 0.01, the τ₈₀ value (the time when the PersL intensity decreases to 80% of the initial intensity) increases from 0.24 to 19.61 ms, which proves to be effective in compensating the flicker effect of AC-LEDs. A new method of generating white light emission during the dimming time through adding the blue-light excited cyan PersL phosphor to the original orange-red PersL phosphor was proposed and an AC-LED lamp with a decreased percent flicker of 48.15% was fabricated, which is significantly better than the other currently reported AC-LED devices based on PersL phosphors. These results demonstrate that BaLu₂Al₂Ga₂SiO₁₂:Ce³⁺, Bi³⁺ might be an attractive material for low-flicker AC-LEDs.

Enhanced thermal stability and afterglow performance in Sr2Ga2−xAlxSiO7:Ce3+ phosphors via band gap tailoring

Due to the change of band gap, the photoluminescence and persistent luminescence performances of Ce3+ in Sr2(Ga,Al)2SiO7 have been optimized by the regulation of Al3+/Ga3+.

Tuning emission color and improving the warm-white persistent luminescence of phosphor BaLu2Al2Ga2SiO12:Pr3+via Zn2+ co-doping

In this article, we synthesized a series of new warm-white emitting persistent luminescent phosphors by co-doping Zn²⁺ into Pr³⁺ activated BaLu₂Al₂Ga₂SiO₁₂, and systematically investigated the effect of Zn²⁺ co-doping on both their photoluminescence and persistent luminescence properties. Following the removal of UV excitation, the phosphor emits warm-white persistent luminescence consisting of greenish-blue and red emissions originating from ³P₀ and ¹D₂ multiplet electron transitions at the 4f level of Pr³⁺. The luminescence properties of the Ba_1-xZn_xLu₂Al₂Ga₂SiO₁₂:Pr³⁺ phosphors can be modified by changing the content of Ba/Zn in the host, which affects the non-radiative energy flow between 5d¹-³P₀-¹D₂ levels and resultantly enhances the intensity of the 4f → 4f transition. Compared with the undoped sample, Zn²⁺ co-doping can significantly enhance the persistent luminescence intensity of the phosphors in the range of 400-800 nm and reduce the intensity in the UV region. Meanwhile, Zn²⁺ co-doping can also change the intensity ratio between the greenish-blue and red emissions, and the persistent luminescence color can be tuned from red to warm-white with the increase of Zn²⁺ concentration. Besides, the Zn²⁺ ions entering the crystal lattice also enhance the persistent luminescence performance by modifying the defect levels in the phosphor. For the optimized phosphor, bright warm-white persistent luminescence can be observed by the naked eye in the dark after the removal of the excitation source for 4 h. Based on the experimental results, a feasible mechanism was also proposed to reveal the persistent luminescence generation process for the BaLu₂Al₂Ga₂SiO₁₂:Pr³⁺,Zn²⁺ phosphor.

High stability ultra-narrow band self-activated KGaSiO4 long-persistent phosphors for optical anti-counterfeiting

Optical anti-counterfeiting has been developed as a promising optical-sensing technique. A self-activated KGaSiO₄ phosphor was successfully prepared using the traditional solid-state method. The photoluminescence spectra of the as-synthesized phosphors indicate that the ultra-narrow band emission with green light peak at 503 nm is obtained when phosphors are excited by 254 nm UV light. Additionally, the measured afterglow curve shows that the emission of this phosphor can last more than 1200 s after UV excitation stops, which indicates that KGaSiO₄ is a potential candidate for anti-counterfeiting materials. The luminescent and decay mechanism are discussed by theoretical calculation and thermo-luminescent spectra in detail. The theoretical model can provide support for explaining the mechanism of narrow band or persistent phosphor.

Achieving the potential multifunctional near-infrared materials Ca3In2-x Ga x Ge3O12:Cr3+ using a solid state method

Near-infrared spectroscopy is developing rapidly in the fields of human detection and food analysis due to its fast response and non-invasive characteristics. Herein, we report the novel near-infrared garnet-type Ca3In2Ge3O12:xCr3+ and Ca3In2-x Ga x Ge3O12:0.07Cr3+ phosphors, in which there are two crystallographic sites (CaO8, InO6) that can be substituted by Cr3+, and cation regulation engineering for In3+ is utilized to tune the luminescence properties. Under the 480 nm excitation, the Ca3In2Ge3O12:xCr3+ phosphor emits a broad spectrum at 650-1150 nm, which matches well with the first biological window. The concentration quenching mechanism and luminescence mechanism of Ca3In2Ge3O12:xCr3+ were studied and the site assignment of the two luminescence centers was discussed using low temperature spectra and fluorescence decay curves. The application performance of the phosphor was improved by introducing Ga3+ to substitute for In3+, and the blue shift of nearly 50 nm was explained by crystal field and nephelauxetic effects. At the same time, a 24% increase in the activation energy of thermal quenching of phosphors was obtained, which has been analyzed using the mechanism of phonon transition and the change of structural rigidity. Thus, the near-infrared emitting Ca3In0.2Ga1.8Ge3O12:0.07Cr3+ phosphor was obtained, which has lower cost, higher emission intensity, and much better thermal stability, spreading the application of phosphors in plant far red light illumination, human body detection, and spectral conversion technology of silicon-based solar cells. Simultaneously, an example of a near-infrared plant illumination experiment is given, demonstrating that a cation substitution strategy based on crystal field control could be applied to tune spectral distribution and develop novel potential phosphors for practical optical application.

Recent advances in optical and optoelectronic data storage based on luminescent nanomaterials

The substantial amount of data generated every second in the big data age creates a pressing requirement for new and advanced data storage techniques. Luminescent nanomaterials (LNMs) not only possess the same optical properties as their bulk materials but also have unique electronic and mechanical characteristics due to the strong constraints of photons and electrons at the nanoscale, enabling the development of revolutionary methods for data storage with superhigh storage capacity, ultra-long working lifetime, and ultra-low power consumption. In this review, we investigate the latest achievements in LNMs for constructing next-generation data storage systems, with a focus on optical data storage and optoelectronic data storage. We summarize the LNMs used in data storage, namely upconversion nanomaterials, long persistence luminescent nanomaterials, and downconversion nanomaterials, and their applications in optical data storage and optoelectronic data storage. We conclude by discussing the superiority of the two types of data storage and survey the prospects for the field.

Crystal structure, theoretical studies and luminescent properties of a new borate Na3GdB8O15 with one-dimensional broad-banded anionic framework

Inorganic borate compounds exhibit significant diversity in their structure types, which are associated with interesting optical and magnetic properties. In our work, a new rare-earth polyborate Na₃GdB₈O₁₅ was prepared with an infinite one-dimensional (1D) broad-banded framework of [B₈O₁₅]_∞ running along the a-axis, in which large Gd³⁺ and Na⁺ ions reside to ensure cohesion and neutrality of the structure. The basic fundamental building block (FBB) of [B₈O₁₅]_∞ is B₁₆O₃₂, which is composed of five BO₃ and three BO₄ groups and can be written as 5Δ3□: 〈2Δ□〉-〈Δ2□〉〈2Δ□〉. First principle studies reveal that Na₃GdB₈O₁₅ is an indirect bandgap semiconductor and the optical absorption at 280 nm originates from the O^2-→ Gd³⁺ transition. Solid solutions of Na₃Gd_1-xCe_xB₈O₁₅ and Na₃Gd_0.98-yY_yCe_0.02B₈O₁₅ were prepared and exhibited a bluish violet emissive luminescence by near-UV excitation due to the 5d¹→ 4f¹ transition of Ce³⁺. Substitution of Gd³⁺ by Y³⁺ enhanced the luminescence efficiency and significantly improved the thermal stability. At 423 K, the luminescence intensity of Na₃Gd_0.58Y_0.4Ce_0.02B₈O₁₅ remained 77% of that at 298 K. We hypothesize that Na₃GdB₈O₁₅ is a potential inorganic luminescent host matrix.

Strategies for Designing Antithermal-Quenching Red Phosphors

Nowadays, red phosphor plays a key role in improving the lighting quality and color rendering index of phosphor-converted white light emitting diodes (w-LEDs). However, the development of thermally stable and highly efficient red phosphor is still a pivotal challenge. Herein, a new strategy to design antithermal-quenching red emission in Eu3+, Mn4+-codoped phosphors is proposed. The photoluminescence intensity of Mg3Y2(1- y )Ge3O12:yEu3+, Mn4+ (0 ≤ y ≤ 1) phosphors continuously enhances with rising temperature from 298 to 523 K based on Eu3+ → Mn4+ energy transfer. For Mg3Eu2Ge3O12:Mn4+ sample, the integrated intensity at 523 K remarkably reaches 120% of that at 298 K. Interestingly, through codoping Eu3+ and Mn4+ in Mg3Y2Ge3O12, the photoluminescence color is controllably tuned from orangish-red (610 nm) to deep-red (660 nm) light by changing Eu3+ concentration. The fabricated w-LEDs exhibit superior warm white light with low corrected color temperature (CCT = 4848 K) and high color rendering index (R a = 96.2), indicating the promising red component for w-LED applications. Based on the abnormal increase in antistokes peaks of Mn4+ with temperatures, Mg3Eu2Ge3O12:Mn4+ phosphor also presents a potential application in optical thermometry sensors. This work initiates a new insight to construct thermally stable and spectra-tunable red phosphors for various optical applications.

Realizing Efficient Single Organic Molecular White Light-Emitting Diodes from Conformational Isomerization of Quinazoline-Based Emitters

Single pure organic molecular white light emitters (SPOMWLEs) are of significance as a new class of material for white lighting applications; however, few of them are able to emit white electroluminescence from organic light-emitting diodes. Herein, donor-π-acceptor conjugated emitters, 2PQ-PTZ and 4PQ-PTZ, were designed and synthesized as SPOMWLEs for white light emission considering the distinct advantages of their conformation isomers. The coexistence of conformational isomers in 2PQ-PTZ, which is the first experimental evidence of the coexisting quasi-axial and quasi-equatorial conformers, provides ideal flexibility to obtain white light emission from their simultaneous and well-separated fluorescence and thermally activated delayed fluorescence. With these remarkable properties, a 2PQ-PTZ-based white light-emitting diode (LED) with a CIE of (0.32, 0.34) and color rendering index (CRI) of 89 is demonstrated. Further, the white organic light-emitting diode (OLED) of 2PQ-PTZ exhibits a high external quantum efficiency (EQE) of 10.1%, which is the reported highest performance among SPOMWLE-based OLEDs.

Highly Efficient Organic Room-Temperature Phosphorescent Luminophores through Tuning Triplet States and Spin-Orbit Coupling with Incorporation of a Secondary Group

Achieving efficient ultralong purely organic phosphorescent luminophores is still a big challenge due to the slow intersystem crossing (ISC) process. Herein, we present a facile molecular design strategy that incorporates a secondary group (Br atom or methoxy group) into o-BrCz that can significantly enhance the ISC rate constant (k_ISC) and achieve high phosphorescence quantum yields (Φ_P). As a result, DBrCz and MeBrCz achieved a profound increase of k_ISC ≈ 10⁸ s^-1 and obtained excellent Φ_P values up to 24.53 and 27.81% in solid powder, respectively. Given the highly efficient Φ_P and proper τ_p, DBrCz and MeBrCz are applied to alternating current (AC) light-emitting diodes (LEDs), achieving a white LED with CIE coordinates (0.28, 0.29) and a CRI over 90. As a proof of concept, we demonstrate its compensation effect on the dark duration of AC-LED with a reduced percent flicker of 78%. This result extends a new potential application for RTP luminophores in the lighting field.

UV or blue light excited red persistent perovskite phosphor with millisecond lifetime for use in AC-LEDs

Energy storage phosphors with millisecond period afterglow that compensate for the diming time of alternating current light-emitting diodes (AC-LEDs) have promising application. To obtain a persistent luminescence (PersL) white colour in AC-LEDs, we focussed on a red afterglow with short period phosphorescence. Ca₄ Ti₃ O₁₀ forms a type of perovskite-related Ruddlesden-Popper phase structure. Doping Pr³⁺ ions into Ca₄ Ti₃ O₁₀ , an ideal red PersL was obtained. X-ray diffraction and element analysis demonstrated that our target samples were crystallized well. Steady-state and afterglow luminescence properties were investigated in detail. Notably, the PersL intensity was dependent on various excitation wavelengths. By measuring three-dimensional thermoluminescence spectra, we found that the trap depths showed a continuous distribution and that the shallowest trap contributed to the millisecond afterglow. Two PersL mechanism models were used to elucidate the electron charging and de-trapping processes under UV or blue light activation.

Optical Properties of Red-Emitting Rb2Bi(PO4)(MoO4):Eu3+ Powders and Ceramics with High Quantum Efficiency for White LEDs

There are several key requirements that a very good LED phosphor should meet, i.e., strong absorption, high quantum efficiency, high colour purity, and high luminescence quenching temperature. The reported Rb2Bi(PO4)(MoO4):Eu3+ phosphors have all these properties. The Rb2Bi(PO4)(MoO4):Eu3+ phosphors emit bright red light if excited with near-UV radiation. The calculated colour coordinates show good stability in the 77-500 K temperature range. Moreover, sample doped with 50% Eu3+ possesses quantum efficiency close to unity. Besides the powder samples, ceramic disks of Rb2Eu(PO4)(MoO4) specimen were also prepared, and the red light sources from these disks in combination with near-UV emitting LED were fabricated. The obtained results indicated that ceramic disks efficiently absorb the emission of 375 and 400 nm LED and could be applied as a red component in phosphor-converted white LEDs.

Enhanced Persistence Properties through Modifying the Trap Depth and Density in Y3Al2Ga3O12:Ce3+,Yb3+ Phosphor by Co-doping B3

Long persistence phosphors with high emitting intensity are promising materials for safety signage and energy storage applications. Herein, an improved persistent luminescence of Y₃Al₂Ga₃O₁₂ phosphor by co-doping Ce³⁺, Yb³⁺, and B³⁺ is achieved using conventional solid-state reaction. On one hand, the incorporation of H₃BO₃ can improve the crystallinity; on the other hand, B³⁺ can replace Al³⁺/Ga³⁺ in tetrahedral sites in the host lattice, causing lattice contraction and modifying the trap depth and density. It is found that adding B³⁺ forms a much deeper trap with ∼1.10 eV depth. In addition, the density of the electron trap can also be dramatically increased compared to the sample without B³⁺. The charging process for persistent luminescence is demonstrated by comparing the photoluminescence excitation spectrum with the thermoluminescence excitation spectrum. The persistence luminescence mechanism is given by a visual energy level diagram on the basis of the vacuum referred binding energy scheme of Y₃Al₂Ga₃O₁₂.

Trap distribution and mechanism for near infrared long-afterglow material AlMgGaO4:Cr3+

A novel near infrared long afterglow material AlMgGaO₄:Cr³⁺, its trap distribution, and luminescence mechanism.

Tailoring Trap Depth and Emission Wavelength in Y3Al5- xGa xO12:Ce3+,V3+ Phosphor-in-Glass Films for Optical Information Storage

Deep-trap persistent luminescent materials, due to their exceptional ability of energy storage and controllable photon release under external stimulation, have attracted considerable attention in the field of optical information storage. Currently, the lack of suitable materials is still the bottleneck that restrains their practical applications. Herein, we successfully synthesized a series of deep-trap persistent luminescent materials Y₃Al_{5- x}Ga _xO₁₂:Ce³⁺,V³⁺ ( x = 0-3) with a garnet structure and developed novel phosphor-in-glass (PiG) films containing these phosphors. The synthesized PiG films exhibited sufficiently deep traps, narrow trap depth distributions, high trap density, high quantum efficiency, and excellent chemical stability, which solved the problem of chemical stability at high temperatures in the reported phosphor-in-silicone films. Moreover, the trap depth in the phosphors and PiG films could be tailored from 1.2 to 1.6 eV, thanks to the bandgap engineering effect, and the emission color was simultaneously changed from green to yellow due to the variation of crystal field strength. Image information was recorded on the PiG films by using a 450 nm blue-light laser in a laser direct writing mode and the recorded information was retrieved under high-temperature thermal stimulation or photostimulation. The Y₃Al_{5- x}Ga _xO₁₂:Ce³⁺,V³⁺ PiG films as presented in this work are very promising in the applications of multidimensional and rewritable optical information storage.

Spy Must Be Spotted: A Multistimuli-Responsive Luminescent Material for Dynamic Multimodal Anticounterfeiting and Encryption

The development of luminescent materials for anticounterfeiting and encryption is of great importance. Herein, we develop a multistimuli-responsive luminescent material, Na₂CaGe₂O₆:Pb²⁺/Er³⁺, and use it to print luminescent images. The photoluminescence and upconversion luminescence of these images show different patterns and colors under different stimuli. The photostimulated luminescence (PSL) of the printed images causes dynamic changes in appearance and is accordingly applied for dynamic multimodal anticounterfeiting on banknotes. The PSL of these luminescent images is also applied in a virtual war scenario to demonstrate that the dynamic PSL-encrypted information in the fabricated image is sufficiently safe even in extreme cases and that spies will be detected. These results can inspire us with more creative security designs based on this luminescent material.

Formation of Deep Electron Traps by Yb3+ Codoping Leads to Super-Long Persistent Luminescence in Ce3+-Doped Yttrium Aluminum Gallium Garnet Phosphors

The Y₃Al₂Ga₃O₁₂:Ce³⁺-Cr³⁺ compound is one of the brightest persistent phosphors, but its persistent luminescence duration is not so long because of the relatively shallow Cr³⁺ electron trap. To compare the vacuum referred binding energy of the electron trapping state by Cr³⁺ and lanthanide ions, we selected Yb³⁺ as a deeper electron trapping center. The Y₃Al₂Ga₃O₁₂:Ce³⁺-Yb³⁺ phosphors show Ce³⁺:5d → 4f green persistent luminescence after blue light excitation. The formation of Yb²⁺ was confirmed by the increased intensity of absorption due to Yb²⁺:4f-5d at 585 nm during the charging process. This result indicates that the Yb³⁺ ions act as electron traps by capturing an electron. From the thermoluminescence glow curves, it was found that the Yb³⁺ trap makes a much deeper electron trap with a 1.01 eV depth than the Cr³⁺ electron trap with a 0.81 eV depth. This deeper Yb³⁺ trap provides a much slower detrapping rate of filled electron traps than the Cr³⁺-codoped persistent phosphor. In addition, by preparing transparent ceramics and optimizing Ce³⁺ and Yb³⁺ concentrations, the Y₃Al₂Ga₃O₁₂:Ce³⁺(0.2%)-Yb³⁺(0.1%) as-made transparent ceramic phosphor showed super-long persistent luminescence for over 138.8 h after blue light charging.

Ce3+-Doped garnet phosphors: composition modification, luminescence properties and applications

Garnets have the general formula of A₃B₂C₃O₁₂ and form a wide range of inorganic compounds, occurring both naturally (gemstones) and synthetically. Their physical and chemical properties are closely related to the structure and composition. In particular, Ce³⁺-doped garnet phosphors have a long history and are widely applied, ranging from flying spot cameras, lasers and phosphors in fluorescent tubes to more recent applications in white light LEDs, as afterglow materials and scintillators for medical imaging. Garnet phosphors are unique in their tunability of the luminescence properties through variations in the {A}, [B] and (C) cation sublattice. The flexibility in phosphor composition and the tunable luminescence properties rely on design and synthesis strategies for new garnet compositions with tailor-made luminescence properties. It is the aim of this review to discuss the variation in luminescence properties of Ce³⁺-doped garnet materials in relation to the applications. This review will provide insight into the relation between crystal chemistry and luminescence for the important class of Ce³⁺-doped garnet phosphors. It will summarize previous research on the structural design and optical properties of garnet phosphors and also discuss future research opportunities in this field.

Trap Depth Engineering of SrSi2O2N2:Ln2+,Ln3+ (Ln2+ = Yb, Eu; Ln3+ = Dy, Ho, Er) Persistent Luminescence Materials for Information Storage Applications

Deep-trap persistent luminescence materials exhibit unique properties of energy storage and controllable photon release under additional stimulation, allowing for both wavelength and intensity multiplexing to realize high-capacity storage in the next-generation information storage system. However, the lack of suitable persistent luminescence materials with deep traps is the bottleneck of such storage technologies. In this study, we successfully developed a series of novel deep-trap persistent luminescence materials in the Ln²⁺/Ln³⁺-doped SrSi₂O₂N₂ system (Ln²⁺ = Yb, Eu; Ln³⁺ = Dy, Ho, Er) by applying the strategy of trap depth engineering. Interestingly, the trap depth can be tailored by selecting different codopants, and it monotonically increases from 0.90 to 1.18 eV in the order of Er, Ho, and Dy. This is well explained by the energy levels indicated in the host-referred binding energy scheme. The orange-red-emitting SrSi₂O₂N₂:Yb,Dy and green-emitting SrSi₂O₂N₂:Eu,Dy phosphors are demonstrated to be good candidates of information storage materials, which are attributed to their deep traps, narrow thermoluminescence glow bands, high emission efficiency, and excellent chemical stability. This work not only validates the suitability of deep-trap persistent luminescence materials in the information storage applications, but also broadens the avenue to explore such kinds of new materials for applications in anticounterfeiting and advanced displays.

Origin of Spectral Blue Shift of Lu3+-Codoped YAG:Ce3+ Phosphor: First-Principles Study

Lu³⁺, with the smallest ionic radii in lanthanide ions, is an important and beneficial cation for tuning spectrum shifting toward a longer wavelength by ion substitution in many phosphors for solid-state lighting. However, in the Lu³⁺-substituted garnet system, the phosphor always has smaller lattice parameters and exhibits a shorter emission wavelength than other garnet phosphors. The mechanism of such a spectral blue shift induced by the Lu³⁺-codoped garnet phosphor is still unclear. In this study, the local and electronic structures of Lu³⁺-codoped and Lu³⁺-undoped YAG:Ce³⁺ phosphor have been studied by first-principles calculation to reveal the origin of the spectral blue shift. Our results provide a full explanation of the experimental data and the methodology, which is useful to understand and design garnet phosphors with tunable emission characteristics.

Cation substitution induced novel gehlenite Ca2GaAlSiO7:Eu2+/Ce3+phosphor with green/blue emission for UV-WLEDs

We have investigated the structure and luminescence properties of a novel and efficient Ca₂GaAlSiO₇:Eu²⁺/Ce³⁺phosphor obtained by cation substitution for UV-WLEDs.

A two-step solid-state reaction to synthesize the yellow persistent Gd3Al2Ga3O12:Ce3+phosphor with an enhanced optical performance for AC-LEDs

The internal quantum efficiency of the GAGG:Ce³⁺persistent phosphor was enhanced to 82% by our proposed two-step reaction method.

Long persistent phosphors—from fundamentals to applications

We present multidisciplinary research on synthetic methods, afterglow mechanisms, characterization techniques, material kinds, and applications of long persistent phosphors.