Solid-state Lighting Applications Research Articles

Photoluminescence features of trivalent holmium doped Ca2La8(SiO4)6O2 phosphors

Abstract This study examines the optical properties of Ca2La8−x (SiO4)6O2:xHo3+ phosphors derived using the sol–gel method. X-ray diffraction data and Rietveld analysis confirmed that the phosphors formed in hexagonal phase with an average estimated crystalline size of 27 nm. The prominent excitation peak observed at wavelength 463 nm corresponding to excitation energy 2.68 eV was due to the 5I8 → 5G6 + 5F1 transition. The photoluminescence emission spectra revealed that the synthesized phosphors emitted in the green color region with the 5S2 + 5F4 → 5I8 transition, releasing 2.27 eV energy. The emission and excitation analyses revealed the presence of concentration quenching as the Ho3+ concentration exceeded 0.03 mol in the Ca2La8−x (SiO4)6O2:xHo3+ series. Further, photometry analysis demonstrated a color purity exceeding 94 %, which supports the candidacy of these phosphors for solid-state lighting applications.

Luminescence Studies on Dy3+ Doped Calcium Aluminum Borosilicate (CABS) Glasses for White Light Emission and Applications in w-LEDs.

Dy3+ doped calcium aluminum borosilicate (CABS) glasses have been synthesized via quick melt quench technique. CABS: xDy3+ glasses (x = 0.1, 0.5, 1, 1.5 and 2mol%) were subjected to various morphological and photoluminescence studies. X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy were conducted to study the structural and bonding nature of the undoped glass. The excitation spectra of Dy3+ doped CABS glasses under 574nm emission show many sharp peaks amongst which the transition from 6H15/2 → 6P7/2 (351nm) had the highest intensity. Under 351nm excitation, glasses exhibit sharp peaks in the blue, yellow and red regions corresponding to the transitions 4F9/2 → 6H15/2, 6H13/2, 6H11/2 and 6H9/2 respectively. The dipole-dipole nature of the interaction between the Dy3+ ions is confirmed via Dexter theory and Inokuti-Hirayama (I-H) model. CIE coordinates estimated from the emission profiles of these glasses under 351nm excitation fall in the white region. Considering that these glasses exhibit sharp visible emission under UV excitation, have stable yellow to blue (Y/B) ratios and fast decays with intense energy transfers, we propose to utilise these glasses for white light generation and other white light LED (w-LED) and solid-state lighting (SSL) applications.

Orange-emitting zero-dimensional Te4+-Doped Cs2ScCl5·H2O perovskite microcrystals

Low-dimensional metal halide perovskites have gained the favor of many researchers for their potential applications in solid-state lighting due to their excellent optoelectronic properties. Herein, Te4+ doped Cs2ScCl5·H2O, a novel orange-emitting zero-dimensional scandium halide perovskite microcrystal was synthesized by hydrothermal method. Cs2ScCl5·H2O is isomorphic to Cs2InCl5·H2O with the space group Pnma. Under UV excitation, Cs2ScCl5·H2O:Te4+ exhibits a bright orange emission at 620 nm with a full width at half maximum (FWHM) of 170 nm, which is related to the formation of self-trapping excitons (STEs) in the zero-dimensional Te4+ doped Cs2ScCl5·H2O soft lattice. The fluorescence lifetime of Cs2ScCl5·H2O:Te4+ microcrystals are highly temperature-dependent with significant changes from microseconds (5.352 μs) at 110 K to nanoseconds (252 ns) at 298 K. The microcrystal-based white LED and thin film were initially explored for their potential application. These findings provide new insights into the excited state dynamics of Te4+ in Cs2ScCl5·H2O and demonstrate the potential application prospect for lead-free scandium halides doped by ns2 metal ions.

Flexible and luminescent polymer nanocomposite films (YPO4:Pr3+/ polystyrene): Investigation of structural, morphological and photoluminescence properties for solid-state lighting applications

Luminescent polymer films are promising for future optoelectronic devices owing to their ease of synthesis, tunable properties and flexibility. The present work reports on the fabrication of YPO4:Pr3+/polystyrene based flexible and luminescent nanocomposite (NC) films followed by an investigation of their structural, morphological and photoluminescence properties for their potential applications in optical devices. NC films were successfully prepared by direct solution mixing of YPO4: Pr3+ (0.1, 2 at. %) luminescent nanoparticles (NPs) and polystyrene (PS). X-ray diffraction (XRD) analysis of NC films revealed an improvement in crystallinity upon increasing YPO4: Pr3 NPs doping into PS films. The emission spectra of the pure and YPO4:Pr3+/PS NC films under UV excitation at 223 nm showed the same features with a broad emission band in the 280–400 nm region. However, an increase in emission intensity, and absence of interconfigurational emission characteristic of the YPO4: Pr3+ NPs were observed in UV region, due to the strong absorption band of PS in this region. Upon doping, YPO4:Pr3+ NPs were found to reduce their intrinsic luminescence emission from interconfigurational transitions of Pr3+ ions. However, it was dominated by an orange-red luminescence of 1D2→3H4 transition, while, no emission was observed for the PS film owing to its transparency in the visible region. The fluorescence decay times of 1D2→3H4 in the NC films were shorter as compared to those of the original NPs. Chromatic coordinates and correlated color temperature indicated that the YPO4:Pr3+/PS NC films are promising polymer-phosphors for lighting applications.

Influence of Mn2+ and Eu3+ Concentration on Photoluminescence and Thermal Stability Properties in Eu3+-Activated ZnMoO4 Red Phosphor Materials.

The integration of trivalent europium ion (Eu3+)-doped zinc molybdate (ZnMoO4) as red phosphors in next-generation solid-state lighting (SSL) is impeded by their extended electron lifetime and suboptimal thermal stability. To overcome these limitations, we propose a co-doping approach by incorporating Mn2+ and Eu3+ in ZnMoO4, aiming to improve thermal reversibility and reduce the lifetime of electron transitions. A series of Eu3+-doped ZnMoO4 and Mn2+/Eu3+-co-doped ZnMoO4 phosphor materials were synthesized via the conventional sol-gel method, and their photoluminescence properties were compared under high-temperature conditions. Experimental results indicate that the introduction of Mn2+ into Eu3+-doped ZnMoO4 leads to a decrease in quantum efficiency and electron lifetime, primarily attributed to defects within the crystal lattice and energy transfer from Eu3+ to Mn2+, resulting in enhanced non-radiative transitions. However, the addition of a small quantity of Mn2+ remarkably improves the thermal stability and reversibility of the phosphors. Consequently, this co-doping strategy presents a promising avenue for expanding the application possibilities of phosphor materials, particularly for high-power SSL applications subjected to elevated temperatures. Hence, Eu3+-only doped samples are well-suited for lighting applications due to their high IQE and excellent thermal stability. Conversely, Eu3+/Mn2+-co-doped samples show promise in applications that require a shorter electron lifetime and good reversibility.

Synthesis and luminescent properties of Na5(La,Y) (MoO4)4: Sm3+ phosphors for solid-state lighting application

The Sm3+ and La3+ co-doped Na5Y(MoO4)4 orange-red phosphors were synthesized by solid phase method at 600 °C. The crystal structure, phase purity, thermal stability, and luminescence performance were comprehensively analyzed. Under 405 nm excitation, the phosphors emit the orange-red light because of the 4G5/2-6H5/2, 4G5/2-6H7/2, 4G5/2-6H9/2, and 4G5/2-6H11/2 transitions of Sm3+ ions. The enhancement of emission intensity with La3+ ions doping in phosphors is due to the environmental effect of the crystal field around the luminous center. When it is combined with commercial LED chips, the device emits orange-red light, and the luminescence spectrum coincides with the PR pigment absorption spectrum of the plant, indicating that the potential of Sm3+ and La3+ co-doped Na5Y(MoO4)4 phosphors in solid-state lighting application.

Two-site occupancy induced a broadband blue-emitting in Eu2+ doped Na3Ba2Ca(PO4)3 phosphor

During the process of developing commercial chips, the phosphors with single broadband emission are indispensable. In this report, a new ternary phosphate phosphor Na3Ba2Ca(PO4)3:Eu2+ has been successfully synthesized by the high-temperature solid-state reaction (HSSR) method, which shows broad emitting band in the range of 350–600 nm centered at 436 nm (FWHM ∼ 72.3 nm). The crystal structure of the Na3Ba2Ca(PO4)3 and Eu2+ doped Na3Ba2Ca(PO4)3 were determined by the Rietveld method, indicating the trigonal system with P31c space group. The selective two-site occupancy tendency of Eu2+ ions at Ba1O9 and Ca2O8 sites in the matrix was comprehensively revealed according to the split peaks (433 nm and 469 nm) at 298 K and 11 K, computational validation and fluorescence lifetime analysis of photoluminescence spectrum. Impressively, the optimal Na3Ba2Ca(PO4)3:0.02Eu2+ phosphor exhibits appropriate spectrum resemblance (SR) indexes (58.5% and 72.2%), proper thermostability (78.6%) and excellent chromaticity stability (Δx = 8.68 × 10−6 and Δy = 3.64 × 10−5). Besides, the phosphor prepared by HSSR owns the higher internal quantum efficiency of 62.1% in comparison with that synthesized by polymerizable complex (PC) method. The new phosphor can serve as a potential broadband and blue-emitting phosphor for the application of solid-state lighting and plant growth.

Double-perovskite structure-driven thermal-stabilized Dy3+-activated yellow-emitting phosphors

A series of novel dysprosium(III) (Dy3+)-doped yellow-emitting double-perovskite A2BB’O6 (A = calcium(II) (Ca2+), B = lanthanum(III) (La3+), gadolinium(III) (Gd3+), and indium(III) (In3+); B′ = antimony(V) (Sb5+), tantalum(V) (Ta5+), and niobium(V) (Nb5+)) phosphors were synthesized. The ion substitution in B and B′ sites in the double-perovskite structure significantly affected its crystal structures and photoluminescence properties such as excitation spectrum, emission spectrum, thermal stability, color purity, luminescence dynamic, and quantum yield. Interestingly, the beneficial thermal stability of all the obtained samples (> 62% at 423 K with respect to the initial value at 303 K) implied their potential for solid-state lighting application. Among them, the Ca2LaTaO6:Dy3+ exhibited the best heat resistance (> 83% at 423 K) while the Ca2GdNbO6:Dy3+ had the highest internal quantum yield up to 35.17%. Furthermore, the possible mechanisms for the changes in luminescent properties relying on their chemical compositions were studied accordingly. Eventually, some fabricated light-emitting diode devices based on the obtained samples were tested for their application in warm solid-state lighting.

Optimized Tb3+-activated highly efficient green-emanating BaLa2ZnO5 nanophosphors in PDMS matrix for flexible display, anti-counterfeiting, and dermatoglyphics applications

Green-emitting BaLa2ZnO5:Tb3+ nanophosphors (NPs) were synthesized via a safe and cost-effective solution combustion process, with Tb3+ dopant content optimized at 4 mol% to avoid concentration quenching. The NPs exhibited strong green emission at 545 nm, a decay lifetime of 0.520 ms, and a quantum efficiency of 35.12%. Chromaticity generalization demonstrated their potential for advanced lighting devices, with coordinate values of (0.2669, 0.5274), a temperature of 7246 K, and color purity of 91.03%. The optimized NPs produced a proof-of-concept security ink and a translucent anti-counterfeiting (AC) film that could emit a powerful green light when exposed to UV light. A Python program was developed to enhance and extract features from fingerprints, emphasizing the importance of each step in producing a perfectly improved image. The minutiae FPs were color-coded to indicate bifurcation and termination, and the final stage of thinning and binarizing images revealed Level-I and Level-II features. The optimized BLZO:4Tb3+ NPs demonstrated great potential for solid-state lighting, flexible displays, anti-counterfeiting, and dermatoglyphics applications.

An investigation on the cyclic temperature-dependent performance behaviors of ultrabright air-stable QLEDs

The aerobic and thermal stability of quantum-dot light-emitting diodes (QLEDs) is an important factor for the practical applications of these devices under harsh environmental conditions. We demonstrate all-solution-processed amber QLEDs with an external quantum efficiency (EQE) of > 14% with almost negligible efficiency roll-off (droop) and a peak brightness of > 600,000 cd/m2, unprecedented for QLEDs fabricated under ambient air conditions. We investigate the device efficiency and brightness level at a temperature range between − 10 and 85 °C in a 5-step cooling/heating cycle. We conducted the experiments at brightness levels higher than 10,000 cd/m2, required for outdoor lighting applications. Our device performance proves thermal stability, with minimal standard deviation in the performance parameters. Interestingly, the device efficiency parameters recover to the initial values upon returning to room temperature. The variations in the performance are correlated with the modification of charge transport characteristics and induced radiative/non-radiative exciton relaxation dynamics at different temperatures. Being complementary to previous studies on the subject, the present work is expected to shed light on the potential feasibility of realizing aerobic-stable ultrabright droop-free QLEDs and encourage further research for solid-state lighting applications.

Achieving Highly Efficient Warm-White Light Emission in All-Inorganic Copper-Silver Halides via Structural Regulation.

Single-component metal halides with white light emission are highly attractive for solid-state lighting applications, but it is still challenging to develop all-inorganic lead-free metal halides with high white-light emission efficiency. Herein, by rationally introducing silver (Ag) into zero-dimensional (0D) Cs3 Cu2 Br5 as new structural building unit, a one-dimensional (1D) bimetallic halide Cs6 Cu3 AgBr10 is designed that emits strong warm-white light with an impressive photoluminescence quantum yield (PLQY) of 94.5% and excellent stability. This structural transformation lowers the conduction band minimum while maintaining the localized nature of the valence band maximum, which is crucial in expanding the excitation spectrum and obtaining efficient self-trapped excitons (STEs) emission simultaneously. Detailed spectroscopy studies reveal that the white-light originates from triplet STEs emission, which can be remarkably improved by weakening the strong electron-phonon coupling and thus suppressing phonon-induced non-radiative processes. Moreover, the interesting temperature-dependent emission behavior, together with self-absorption-free property, make Cs6 Cu3 AgBr10 as sensitive luminescent thermometer and high-performance X-ray scintillator, respectively. These findings demonstrate a general approach to achieving effective single-component white-light emitters based on lead-free, all-inorganic metal halides, thereby opening up a new avenue to explore their versatile applications such as lighting, temperature detection and X-ray imaging.

Orange-red luminescence of samarium-doped bismuth-germanium-borate glass for light-emitting devices.

Samarium (Sm3+ )-doped glass has sparked a rising interest in demonstrating a noticeable emission in the range of 400-700, which is advantageous in solid-state lasers in the visible region, colour displays, undersea communication, and optical memory devices. This study reports the fabrication of Sm3+ -doped bismuth-germanium-borate glasses were established using a standard melt-quenching technique and inspection by absorption, steady-state luminescence, and transient studies. The typical peaks of Sm3+ ions were detected in the visible range under 403 nm excitation. A strong emission band was detected at 599 nm that resembles the 4 G5/2 →6 H7/2 transition of Sm3+ ions for BGBiNYSm0.5 glass. Furthermore, a reddish-orange (coral) luminescence at 646 nm that resembles the 4 G5/2 →6 H9/2 transition was also perceived. The stimulated emission cross-section of 4 G5/2 level for BGBiNYSm0.5 glass was 0.39 × 10-22 cm2 . Lifetime of the 4 G5/2 level was enhanced for the BGBiNYSm0.5 glass and decreased with an increase in active ion concentrations. The lifetime quenching of ions at the metastable state was because of energy transfer among Sm3+ ions by cross-relaxation channels. Commission Internationale de l'Éclairage (CIE) coordinates were evaluated from the emission spectra. Moreover, all the findings recommend these glass as light-emitting materials in the coral region at 599 nm for solid-state lighting applications.

Simultaneous Enhancement of the Luminescence Intensity and Stability of Deep-Red CsPbI3 Perovskite Quantum Dots Achieved by a Doping Strategy.

The phase instability of CsPbI3 perovskite quantum dots (PQDs) restricts their practical applications due to the easy conversion from the luminescent cubic phase to the non-luminescent orthorhombic phase. The elemental doping route has been regarded as one of the most effective strategies to achieve high-quality PQDs-based phosphors. Herein, a stoichiometric amount of nickel chloride (NiCl2) has been effectively doped into the CsPbI3 lattice. The incorporation of Ni2+ ions has little effect on the crystal phase, structure, and morphology of the CsPbI3 PQDs but greatly influences their luminescence properties. The Ni2+ doping not only improves the luminescence performance but also greatly enhances the stability against temperature, storage time, and polar solvent. The formation process and luminescence and stability improvement mechanisms have been discussed. Moreover, the influence of a series of other metal chlorides (KCl, NaCl, MgCl2, ZnCl2, SnCl2, and CaCl2) on the luminescence performance of CsPbI3 PQDs has been systematically investigated, revealing that the luminescence intensity increases by introducing CaCl2, SnCl2, or ZnCl2 but decreases after doping MgCl2, NaCl, or KCl into the CsPbI3 lattice. The as-proposed doping strategy may have a significant impact on tackling the intrinsic instability of all-inorganic CsPbX3 PQDs, shedding light on their future applications in light-emitting diode (LED) devices and solid-state lighting.

Crystal Phase Refinement and Optical Features of Highly Efficient Green Light Radiating Ca9Y(VO4)7: Er3+ Nanophosphors for Emerging Solid-state Lighting Applications.

Ca9Y(VO4)7 phosphor activated with Er3+ ions have been developed by the urea-aided solution combustion technique. XRD profiles assisted with Rietveld refinement executed over-developed Er3+-activated Ca9Y(VO4)7 powder, revealed a trigonal phase with the R3c space group. The electron microscope techniques namely TEM and SEM characterize the size and surface-linked qualities of the developed nanopowder, respectively. The uniform distribution of various elements in the nanocrystalline sample is authenticated by an energy-dispersive spectroscopy (EDS) system. The Eg (band gap) value of 3.64eV for Ca9Y0.9Er0.1(VO4)7 and 3.74eV for Ca9Y(VO4)7 has been estimated. Upon 382nm excitation, Er3+: Ca9Y(VO4)7 phosphor gives rise to the bright green emission owing to the 4S3/2 → 4I15/2 transition. The concentration quenching after 10mol% composition of trivalent erbium ions is attributed to dipole-dipole interlinkages in accordance with Dexter's theory. The radiative lifetime (1.1083 ms), non-radiative rates (0.2079 ms- 1), quantum efficiency (79%), along with colorimetric parameters i.e. CIE x (= 0.2577), y (= 0.4566), and CCT quantities offer Ca9Y0.9Er0.1(VO4)7 as a proficient green radiating nanomaterial for RGB phosphors in solid-state applications.

Effect of SiO2 shell on photoluminescence enhancement of Eu3+ doped nanophosphor based on monoclinic Y2O3

Surface SiO2 coating strategy was used to enhance the photoluminescent properties of Eu3+ doped nanophosphor based on monoclinic Y2O3. Laser-synthesized m-Y2O3:Eu3+ spherical nanoparticles with high crystallinity and diameter of ca. 18 nm were used as a core for the preparation of m-Y2O3:Eu3+@SiO2 core-shell structures. According to HRTEM and HAADF-STEM data, a thin SiO2 shell uniformly encapsulated the crystal core with a thickness of about 1.5 nm. The SiO2 shell increases the absolute photoluminescence quantum yield of Eu3+ at λ = 395 nm excitation from 14 % to 68 %. To the best of our knowledge, the obtained quantum yield exceeds the known values for Eu3+ doped oxide-based nanophosphors and is comparable to those of some other commercial red microphosphors. The SiO2 coating was shown to reduce the luminescence quenching effect associated with the annealing-induced migration of Eu3+ from the bulk to the surface of nanoparticles. The obtained results demonstrate that m-Y2O3:Eu3+@SiO2 core-shell nanoparticles with intense red luminescence have significant potential for use in LEDs, high resolution displays, bioimaging technologies and in other solid-state lighting applications.

Zero-Dimensional Halides with ns2 Electron (Sb3+) Activation to Generate Broad Photoluminescence.

Organic-inorganic metal halides (OIMHs) have various crystal structures and offer excellent semiconducting properties. Here, we report three novel OIMHs, (PPA)6InBr9 (PPA = [C6H5(CH2)3NH3]+), (PBA)2SbBr5, and (PBA)2SbI6 (PBA = [C6H5(CH2)4NH3]+), showing typical zero-dimensional (0D) structure, octahedra dimers, and corner-sharing one-dimensional chains and crystallized in the monoclinic system with P21, P21/c, and C2/c space groups, respectively. (PPA)6InBr9, (PBA)2SbBr5, and (PBA)2SbI6 have experimental optical band gaps of ∼3.16, ∼2.24, and 1.48 eV, respectively. (PPA)6InBr9 exhibits bright-orange light emission centered at 642 nm with a full-width at half-maximum of 179 nm (0.51 eV) and a Stokes shift of 277 nm (1.46 eV). After Sb3+ doping, the peak position did not change, and the photoluminescence quantum yield increased significantly from 9.2 to 53.0%. The efficient emission of Sb:(PPA)6InBr9 stems from the isolated ns2 luminescent center and strong electron-phonon coupling, making the spin-forbidden 3P1-1S0 observable. By combining commercial blue and green phosphors with orange-red-light-emitting (PPA)6In0.99Sb0.01Br9, a white-light-emitting diode was constructed, with the color-rendering index reaching up to 92.3. Our work highlights three novel 0D OIMHs, with chemical doping of Sb3+ shown to significantly enhance the luminescence properties, demonstrating their potential applications in solid-state lighting.

Ultra-Narrow-Bandwidth Deep-Red Electroluminescence Based on Green Plant-Derived Carbon Dots.

Deep-red light-emitting diodes (DR-LEDs, >660nm) with high color-purity and narrow-bandwidth emission are promising for full-color displays and solid-state lighting applications. Currently, the DR-LEDs are mainly based on conventional emitters such as organic materials and heavy-metal based quantum dots (QDs) and perovskites. However, the organic materials always suffer from the complicated synthesis, inferior color purity with full-width at half-maximum (FWHM) more than 40 nm, and the QDs and perovskites still suffer from serious problems related to toxicity. Herein, this work reports the synthesis of efficient and high color-purity deep-red carbon dots (CDs) with a record narrow FWHM of 21nm and a high quantum yield of more than 50% from readily available green plants. Moreover, an exciplex host is further established using a polymer and small molecular blend, which has been shown to be an efficient strategy for producing high color-purity monochrome emission from deep-red CDs via Förster energy transfer (FET). The deep-red CD-LEDs display high color-purity with Commission Internationale de l'Eclairage (CIE) coordinates of (0.692, 0.307). To the best of the knowledge, this is the first report of high color-purity CD-LEDs in the deep-red region, opening the door for the application of CDs in the development of high-resolution light-emitting display technologies.

Formation and Photophysical Properties of Silver Clusters in Bulk of Photo-Thermo-Refractive Glass

The bright luminescence of silver clusters in glass have potential applications in solid-state lighting, optical memory, and spectral converters. In this work, luminescent silver clusters were formed in the bulk of photo-thermo-refractive glass (15Na2O-5ZnO-2.9Al2O3-70.3SiO2-6.5F, mol.%) doped with different Ag2O concentrations from 0.01 to 0.05 mol.%. The spontaneous formation of plasmonic nanoparticles during glass synthesis was observed at 0.05 mol.% of Ag2O in the glass composition, limiting the silver concentration range for cluster formation. The luminescence of silver clusters was characterized by steady-state and time-resolved spectroscopy techniques. The rate constants of fluorescence, phosphorescence, intersystem crossing, and nonradiative deactivation were estimated on the basis of an experimental study. A comparison of the results obtained for the photophysical properties of luminescent silver clusters formed in the ion-exchanged layers of photo-thermo-refractive glass is provided.

Improved Luminous Efficiency of AgInS2 Quantum Dots and Zeolitic Imidazolate Framework-70 Composite for White Light Emitting Diode Applications.

The application of multiple quantum dots (QDs) in the field of white light emitting diodes (WLEDs) is still an important challenge due to their low luminous efficiency and quenching phenomenon. In this paper, we prepared AgInS2 QDs/zeolitic imidazolate framework-70 (AIS/ZIF-70) composite by a microwave hydrothermal method. Owing to the high porosity and stability of ZIF-70, it could effectively prevent quenching issues due to the aggregation of QDs. Since the ZIF-70 and QDs were chemically bonded, the formation of the ZnS layer could effectively passivate the surface defect and thus the quantum yield reached 21.49 % in aqueous solution. The luminous efficiency (LE) of the assembled AIS/ZIF-based WLED was reinforced by 6.8 times with a molar ratio of AgIn/Zn=18, i. e. at 5.26 % molar fraction of ZIF-70. Moreover, the color rendering index (CRI) and correlated color temperature (CCT) of AIS/ZIF-based WLED were 84.3 and 3631 K, respectively, indicating its potential application in solid-state lighting.

Luminescence properties of Tb3+/Eu3+ ions activated LiLaSiO4 phosphors for solid-state lighting and flexible display applications

The synthesis and luminescence properties of Tb3+ and Eu3+ single- and co-doped LiLaSiO4 (LLSO) phosphors with energy transfer mechanisms were reported. The rare-earth ions doped LLSO phosphors were synthesized via a solid-state reaction method and their physical characterizations such as phase purity, surface morphology, and elemental analysis were investigated systematically. For the Tb3+ and Eu3+ single- and co-doped LLSO phosphors, their photoluminescence (PL) properties were studied in detail. The LLSO:Tb3+ and LLSO:Eu3+ single-doped phosphors showed superior red and green emissions due to 5D4→7F5 and 5D0→7F2 in the optimized characteristic electronic transitions under ultraviolet (UV) irradiation, respectively. The luminescence performances for both the LLSO:Tb3+ and LLSO:Eu3+ phosphors were optimized at 0.125 mol of doping ion concentration. Under UV excitation, by adjusting the Eu3+ ion concentration in LLSO:0.125Tb3+/Eu3+ phosphors, the tunable emissions from green to red via yellow-orange were obtained. Thus, the tunable emission spectra and luminescence decay lifetimes with increasing the doping content of acceptor ions (Eu3+) confirmed an efficient energy transfer from Tb3+ to Eu3+ ions in the co-doped samples. The critical distance between Tb3+ and Eu3+ was determined to be 13.26 Å and the energy transfer mechanism from Tb3+ to Eu3+ ions was demonstrated to be a dipole-dipole mechanism interaction. In addition, the temperature-dependent PL study was carried out for the LLSO:0.125Tb3+/0.025Eu3+ co-doped phosphor sample and it showed better thermal stability against the temperature quenching. The Tb3+ and Eu3+ single- and co-doped LLSO/polydimethylsiloxane (PDMS) flexible composite films were fabricated by mixing the phosphor powders and PDMS solution. Benefiting from the effective protection of the PDMS matrix, the luminescence stability of the composite films was greatly enhanced. Based on the excellent properties of the synthesized phosphors, Tb3+ and Eu3+ single-doped and Tb3+/Eu3+ co-doped LLSO phosphors could serve as a single-phase multicolor-emitting phosphor under UV excitations.