Solid-state Lighting Applications Research Articles

Green Emission of Erbium Doped SYW Phosphors for Optical Thermometry And Solid‐State Lighting

AbstractA series of Er3+ ions doped Sr9Y2W4O24 (SYW) phosphors have been synthesised using solid‐state reaction technique. For optical thermometry and solid state lighting applications, the crystal structure, morphological, and luminescence features of the SYW : Er3+ phosphors were explored. X‐ray diffraction (XRD) reveal that synthesized phosphors having single phase with a tetragonal crystal structure and I41/a space group. Scanning electron microscopy (SEM) was used to examine the morphological behaviour and presence of composition elements. The optical bandgap of the phosphor was evaluated using UV‐Vis diffuse reflection spectra (DRS). The photoluminescence (PL) emission spectra were captured under 380 nm excitation, and the peak with the maximum intensity was identified at 563 nm ascribed to transition 4S3/2→4I15/2, that emits green color in visible region. The temperature dependent PL (TD‐PL) spectra show that SYW phosphor is substantially more thermally stable, having thermal activation energy of about 0.247 eV. Additionally, the fluorescence intensity ratio (FIR) was used to study the optical sensing characteristics of the thermal quenching transitions (2H11/2, 4S3/2) with maximum relative sensitivity (SR) and an absolute sensitivity (SA) being 1.33 % K−1and 0.307 % K−1, respectively. All of the aforementioned findings demonstrate that SYW : Er3+ ions doped phosphors have potential for optical thermometry and other photonic devices.

Synthesis, characterization, and enhanced photoluminescence of ZrO2:Dy3+ phosphors by incorporating Li+, Na+ and K+ ions for LED applications

ZrO2:(0.01)Dy3+:xA+ (A = Li+, Na+ and K+) phosphors were prepared by one step solution combustion method. X-ray diffraction (XRD), reveal formation of different phases. Functional group presence and its vibrations are assigned from FTIR measurements. Influence of alkali metal ions (A+) on surface morphology were realized from SEM micrograph. XPS study was carried out to confirm the presence of Li+ ions. Photoluminescence (PL) spectra of the samples excited at 350 nm exhibited two strong emission peaks at 480 nm and 580 nm, which are characteristic transitions of Dy3+ ions. However, the relative intensity between these peaks varies considerably due to the variation of the co-dopant/compensator (Li+, Na+, K+) concentration, representing the variation of the crystal field. Effects of different charge compensators (A+) and their concentration on the structural and luminescence properties of ZrO2:(0.01)Dy3+:xA+ phosphors were thoroughly investigated. Further, Judd-Ofelt parameters were calculated. Total emission colour (TEC) concentration of ZrO2:(0.01)Dy3+ phosphors were improved remarkably with the addition of charge compensators (A+), which would promote their applications in solid state lighting. The effective blue emission of the phosphors was changing with different co-dopant incorporation. Implying possible use of this material as a blue emitting phosphor as a blue emitting component in three-component white light-emitting diodes (WLEDs).

The emergence and prospects of carbon dots with solid-state photoluminescence for light-emitting diodes.

The significant features of carbon dots (CDs), such as bright and tunable photoluminescence, high thermal stability, and low toxicity, endow them with tremendous potential for application in next generation optoelectronics. Despite great progress achieved in the design of high-performance CDs so far, the practical applications in solid-state lighting and displays have been retarded by the aggregation-caused quenching (ACQ) effect ascribed to direct π-π interactions. This review provides a comprehensive overview of the recent progress made in solid-state CD emitters, including their synthesis, optical properties and applications in light-emitting diodes (LEDs). Their triplet-excited-state-involved properties, as well as their recent advances in phosphor-converted LEDs and electroluminescent LEDs, are mainly reviewed here. Finally, the prospects and challenges of solid-state CD-based LEDs are discussed with an eye on future development. We hope that this review will provide critical insights to inspire new exciting discoveries on solid-state CDs from both fundamental and practical standpoints so that the realization of their potential in optoelectronic areas can be facilitated.

Synergistic interaction of multi-functional additives at the buried interface for efficient blue perovskite light-emitting diodes

The synergistic effect of the doping strategy of basic amino acid salts at the interface enables the simultaneous modification of PEDOT:PSS and the bottom interface of the perovskite film to achieve efficient sky-blue PeLEDs.

The unique luminescent properties and enhanced thermal stability of a novel all-inorganic perovskite CsCaCl3:Mn2+ for solid-state lighting applications

This paper addresses the development and characterization of a novel all-inorganic perovskite crystal, CsCaCl3:Mn2+, which presents remarkable potential for advanced white-light LED applications.

Photoluminescence properties of europium-activated double layered perovskite Sr3Ti2O7 for high-quality lighting applications

Thermally stable double-layered perovskite materials for solid-state lighting applications.

Intense Broadband Emission in the Unconventional 3D Hybrid Metal Halide via High-Pressure Engineering.

Developing hybrid metal halides with self-trapped exciton (STE) emission is a powerful and promising approach to achieve single-component phosphors for wide-color-gamut display and illumination. Nevertheless, it is difficult to generate STEs and broadband emission in the classical and widely used 3D systems, owing to the great structural connectivity of metal-halogen networks. Here, high pressure is implemented to achieve dual emission and dramatical emission enhancement in 3D metal halide of [Pb3 Br4 ][O2 C(CH2 )2 CO2 ]. The pressure-induced new emission is ascribed to the radiation recombination of STEs from the Pb2 Br2 O2 tetrahedra with the promoted distortion through the isostructural phase transition. Furthermore, the wide range of emission chromaticity can be regulated by controlling the distortion order of different polyhedral units upon compression. This work not only constructs the relationship between structure and optical behavior of [Pb3 Br4 ][O2 C(CH2 )2 CO2 ], but also provides new strategies for optimizing broadband emission toward potential applications in solid-state lighting.

Spectroscopic properties, Judd Ofelt analysis of U and Eu activated Li2O-ZnO-SrO-B2O3-P2O5 borophosphate glasses for solid-state lighting applications

Uranium and europium doped borophosphate glasses with the base composition of (Li2O)(ZnO)0.5(SrO)0.4(B2O3)2.55(P2O5)0.5 were synthesized by melt -quenching. The X-ray diffraction profile affirmed that all the synthesized samples were devoid of crystallinity and amorphous in structure. The absence of precipitations/grains in the scanning electron micrographs further validated the amorphous character and compositional homogeneity of the prepared glass. The FTIR spectra revealed several prominent vibrational bands in 713–1568 cm−1 range and were assigned to the corresponding B-O-B and P-O-P and B-O-P bonding. The thermal characteristics of the synthesised glass samples were investigated using differential thermal analysis experiments. The broad photoluminescence (PL) spectra observed for the uranium doped glass with emission maxima at 523 nm resembles the hexavalent U(VI) emission in a disordered amorphous environment. The emission profile of the Eu doped glass displayed several characteristics peaks due to 5D0 → 7FJ transitions. The phonon energy of the base glass was found to be 1005 cm−1. The Judd-Ofelt analysis showed that for all the doped glass, the JO intensity parameter Ω4 was always greater than Ω2 indicating that Eu3+ ions are primarily arranged in a centrosymmetric environment in the studied host. Radiative properties of 5D0 → 7FJ=1-4 transitions of the Eu3+ such as branching ratios, emission cross-section, and transition probabilities were computed. Energy transfer pathways of UO22+ → Eu3+ in the codoped borophosphate glass were described. The CIE chromaticity and PL results suggest that the intense red emission of Eu doped glasses could be useful for phosphor applications.

Systematic First-Principles Calculations of Ce3+-Dopant in Garnet-Type Oxide Phosphors

A study of Ce3+-doped oxide phosphors was performed using first-principles calculations based on the relativistic DV-Xα method. In particular, we focused on the Ce3+-doped garnet-type oxides, which have potential applications in solid-state lighting and display devices. The electronic structure and optical properties of the phosphors were analyzed. The energy levels of the Ce3+ ions were affected by the coordination number and the crystal field strength of the surrounding oxygen ions. In addition, the crystal structure of the material had a significant impact on the energy levels of the Ce3+ ions, with different crystal structures leading to different energy levels.The Ce3+ ion is substitutionally incorporated in the garnet lattice, and the 4f electron of Ce3+ plays an important role in the luminescence of the material. The emission wavelengths of the 5d-4f transition energy of Ce3+ can be tailored by varying the crystal structure and the composition. The 5d orbitals of Ce3+ are substantially affected by the crystal field splitting while the amplitude of crystal field splitting (εcfs) is caused by many parameters: coordination number, symmetry of Ce3+ site, and bond lengths between the Ce3+ ion and the oxygen ions (O2-). This study incorporated the following computational conditions: i) lattice relaxation, ii) the choice of the exchange-correlation potential, and iii) Slater’s transition state method. The effects of these conditions were analyzed. In addition, the correlations among physical properties and electronic structure parameters were also investigated in detail.The first-principles calculation results were compared to the experimental data to validate the accuracy of the theoretical models, which showed a good agreement between the experimental and predicted values.

Synthesis and characterization of thermally stable red light-emitting Eu3+ activated Li7La3Zr2O12 phosphors for solid-state lighting applications

To enhance the photoluminescence property of Li7La3Zr2O12 (LLZO), Eu was doped using a solid-state synthesis technique. X-ray diffraction and Raman spectroscopy analysis were used to examine the crystal structure of the synthesized phosphors. The optical band gap values of pristine and Eu3+ doped LLZO phosphor investigated using ultraviolet-visible (UV-Vis) spectroscopy were measured to be 2.74 and 2.97 eV, respectively. The wavelengths of pure and doped LLZO samples were measured and fitted by the Commission Internationale de l’Eclairage (CIE) chromatic coordinate graph. These samples were found to emit blue emission at 354 nm (pure LLZO) and red emission at 464 nm (doped phosphor), which correspond to the 5D0 to 7Fj (j = 0, 1, 2, and 3) transition. The purity of the color and correlated color temperature with respect to the 0.9 M.W% Eu3+ doped (activated) LLZO sample were estimated to be 80% and 1719K, respectively. The indication of its maximum emissive capability at this rate was found suitable for aesthetic lighting applications.

Spectroscopic properties and thermal stability of a Mn4+-doped polyfluoride phosphor for application in solid-state lighting

In this study, an efficient polyfluoride red-emitting phosphor, Cs3RbGe2F12:Mn4+ (denoted as CRGF:Mn), has been synthesized using a simple co-precipitation method. The crystal and electronic structures, spectroscopic properties, and photoluminescence thermal stability of CRGF:Mn have been systematically characterized. The results show that Mn4+ ions experience a strong crystal field and present a series of intense red emission peaks under blue light excitation. Moreover, CRGF:Mn exhibits a high color purity (95.1 %), high internal quantum efficiency (82.4 %), and enhanced photoluminescence thermal stability at 150 °C, with an intensity of 113 % relative to room temperature. A warm white light-emitting diode exhibiting a low correlated color temperature (3572 K), high color rendering index (90.7), and suitable luminous efficiency (132.6 lm/W) was prepared using CRGF:Mn as a red component, demonstrating viable application in solid-state lighting.

Investigating Fe-doped yttrium oxide nanophosphors for enhanced latent fingerprint visualization and deep learning analysis

In the study, synthesized Fe3+ doped yttrium oxide nanophosphors (Y2O3:Fe NPs, 1–11 mol%), including structural, microstructural, chemical state, optical, thermal, and photoluminescence properties, are extensively studied. An optimized 7 mol % Fe doped Y2O3 NPs powder is used to develop latent fingerprints on various surfaces through a simple powder dusting method. The developed fingerprints are visible under 254 nm UV light. The research also analyzes several pore properties: size, shape, number, position, type, and inter-distance. A fingerprint recognition deep learning model based on the YoLOv8 algorithm was developed and employed for analyzing both single and overlapped fingerprints. These highly effective NPs are also used to create a transparent anti-counterfeiting (AC) ink that exhibits AC properties when exposed to UV light, and their physical and chemical stability opens novel applications in the AC field. The optimized Y2O3:7Fe3+ NPs are an excellent luminous platform for solid-state lighting, AC, and dermatoglyphics applications.

Tilt-induced charge localisation in phosphide antiperovskite photovoltaics

Antiperovskites are a rich family of compounds with applications in battery cathodes, superconductors, solid-state lighting, and catalysis. Recently, a novel series of antimonide phosphide antiperovskites (A 3SbP, where A = Ca, Sr Ba) were proposed as candidate photovoltaic absorbers due to their ideal band gaps, small effective masses and strong optical absorption. In this work, we explore this series of compounds in more detail using relativistic hybrid density functional theory. We reveal that the proposed cubic structures are dynamically unstable and instead identify a tilted orthorhombic Pnma phase as the ground state. Tilting is shown to induce charge localisation that widens the band gap and increases the effective masses. Despite this, we demonstrate that the predicted maximum photovoltaic efficiencies remain high (24%–31% for 200 nm thin films) by bringing the band gaps into the ideal range for a solar absorber. Finally, we assess the band alignment of the series and suggest hole and electron contact materials for efficient photovoltaic devices.

Facile synthesis and photophysical properties of combustion derived Dy3+doped Ca9La(PO4)7 nanophosphors for advanced solid-state lighting applications

Globally, the energy consumption has accelerated, which has driven the research to increase sustainable energy sources. In this context, this is the first report on the exploration of the structural and photometric aspects of Dy3+ doped Ca9La(PO4)7 i.e., CLP: Dy3+ nanophosphors for designing WLEDs economically. Herein, the solution combustion method was utilized for fabricating the desired nanophosphor, thereafter their morphological behavior, and crystallite size were studied in detail via X-ray diffraction, scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) techniques which confirmed the rhombohedral crystal architecture with R3c space group affirming the potential of the fabricated nanomaterials in optoelectronics. CLP: Dy3+nanophosphors depicted reproducible emission spectra with peaks at 4F9/2 → 6H13/2, 15/2 attributed to intra-configurational transitions of Dy3+ ions. The increasing dopant concentration beyond 20 mol % reduced the intensity of emission peaks which could be ascribed to the dipole–dipole interactions of the neighboring ions. The optical band gap of 5.38 eV derived via Kubelka-Munk relations established their role in semiconductors. Moreover, their Commission international de I’eclairge (CIE) chromaticity coordinates were studied in detail to reveal the emission color with color purity and Correlated Color Temperature (CCT) values. All the results favored and exemplified the incredible role of CLP: Dy3+ nanophosphors for emerging future prospects in advanced optoelectronic technology.

Luminescence properties of Eu3+ doped Li2SrSiO4 phosphor

The modified solid-state reaction method has been used in this work to prepare Eu3+ doped Li2SrSiO4. PL spectroscopy was used to investigate photoluminescence (PL) properties of the sample. X-ray powder diffraction study was used to confirm the crystalline nature and phase purity of the sample. The particle size of prepared material ranges from 37 to 56 nm was observed from XRD. From PLE and PL spectrum the excitation and emission spectra of photoluminescence for Eu3+ doped Li2SrSiO4 were recorded. The prepared Eu3+ doped Li2SrSiO4 phosphor might have application in solid state lighting.

Highly efficient and photothermally stable CDs@ZIF-8 for laser illumination

Carbon dots (CDs), as a solid-state phosphor, have great potential for application in a new solid-state lighting device—laser diode (LD). For high efficiency LD devices, both high photoluminescence quantum yield (PLQY) and high photothermal stability of CDs are essential. Herein, yellow CDs@ZIF-8 composites with high structural stability were prepared by encapsulating CDs in zeolitic imidazolate framework-8 (ZIF-8) through electrostatic adsorption between CDs and ZIF-8, in which CDs with amino groups on the surface were used as luminescent feeders and ZIF-8 was used as a protective layer matrix. The as-prepared CDs@ZIF-8 not only possess a high PLQY of up to 81.17%, but also maintain a high fluorescence intensity of 100% and 80% under long-term illumination (60 min) and high temperature (478 K), respectively. The hydrogen bonding between CDs and ZIF-8 in the encapsulated structure can enhance the degree of electron cloud delocalization, which can improve the PLQY of CDs@ZIF-8. Meanwhile, CDs@ZIF-8 has high photothermal stability due to the binding effect of ZIF-8 on CDs and high thermal stability of ZIF-8. The white LD device, fabricated from CDs@ZIF-8 as a phosphor in combination with 450 nm blue LD, has a color coordinate of (0.37, 0.33), a color temperature of 3762 K, and a high color rendering index of 86. This study provides a new strategy for the construction of solid-state phosphors with high PLQY and high photothermal performance.

Multicolor tunable emission through energy transfer in Dy3+/Ho3+ co-doped CaTiO3 phosphors with high thermal stability for solid state lighting applications

The exploration of multicolor emitting phosphors with single phase is extremely important for n-UV chip excited LED/WLED’s and multicolor display devices. In this paper, Dy3+, Ho3+ singly doped and Dy3+/Ho3+ co-doped CaTiO3 phosphor materials have been synthesized by solid state reaction method at 1473 K. The synthesized materials were characterized by XRD, FE-SEM, EDX, FTIR, PL and lifetime measurements. The PL emission spectra of Dy3+ doped CaTiO3 phosphors give intense blue and yellow emissions under UV excitation, while the PL emission spectra of Ho3+ doped CaTiO3 phosphor show intense green emission under UV/blue excitations. Further, to get the multicolor emission including white light, Dy3+ and Ho3+ were co-doped simultaneously in CaTiO3 host. It is found that alongwith colored and white light emissions, it also shows energy transfer from Dy3+ to Ho3+ with 367 nm and from Ho3+ to Dy3+ under 362 nm excitations. The energy transfer efficiency is found to be 67.76% and 69.39% for CaTiO3:4Dy3+/3Ho3+ and CaTiO3:3Ho3+/5Dy3+ phosphors, respectively. The CIE color coordinates, CCT and color purity of the phosphors have been calculated, which show color tunability from whitish to deep green via greenish yellow color. The lifetime of 4F9/2 level of Dy3+ ion and 5S2 level of Ho3+ ion is decreased in presence of Ho3+ and Dy3+ ions, respectively. This is due to energy transfer from Dy3+ to Ho3+ ions and vice versa. A temperature dependent photoluminescence studied of CaTiO3:4Dy3+/2Ho3+ phosphor show a high thermal stability (82% at 423 K of initial temperature 303 K) in the temperature range 303–483 K with activation energy 0.17 eV. The PLQY are 30%, 33% and 35% for CaTiO3:4Dy3+, CaTiO3:4Dy3+/2Ho3+ and CaTiO3:3Ho3+ phosphors, respectively. Hence, Dy3+, Ho3+ singly doped and Dy3+/Ho3+ co-doped CaTiO3 phosphor materials can be used in the field of single matrix perovskite color tunable phosphors which may be used in multicolor display devices, n-UV chip excited LED/WLED’s and photodynamic therapy for the cancer treatment.

Multi-color tunable emission of Bi3+,Eu3+ co-doped Ca3LiZnV3O12 phosphors for warm white light-emitting diodes

Bi3+,Eu3+ co-doped Ca3LiZnV3O12 (CLZV) phosphors were manufactured by conventional high-temperature solid-state reaction technique to explore their application for solid-state lighting. Their crystal structure, luminescent properties, energy transfer processes and quantum efficiency were investigated in detailed. CLZV host can be efficiently excited by 345 nm near-ultraviolet light and exhibit self-activating blue emission. When Bi3+ ions are introduced into CLZV, VO43− and Bi3+ can be co-excited by 345 nm light. Benefiting from energy transfer from VO43− to Eu3+ and Bi3+ to Eu3+, multi-color tuning emission from green to yellow can be observed in CLZV:Bi3+,Eu3+ phosphors. Warm white emission was achieved in CLZV:0.015Bi3+,0.01Eu3+ and CLZV:0.015Bi3+,0.02Eu3+ phosphors. Importantly, their internal quantum efficiencies are 35.2 % and 39.6 %, respectively. Our results indicate that CLZV: Bi3+,Eu3+ phosphors might be promising candidates for white light emitting diodes under ultraviolet excitation.

Fabrication and luminescence properties of Al2O3-Ce:LuAG composite phosphor ceramics for solid-state laser lighting

Introducing Al2O3 as a secondary phase into Ce:LuAG phosphor ceramics has been realized by solid-state reaction method, but there is much room for improvement on the ingredient uniformity and performance of Al2O3-Ce:LuAG composite phosphor ceramics (CPCs). In this work, the excess of Al3+ in (Ce,Lu)3Al5O12 was regulated to synthesize a series of Al2O3-Ce:LuAG multiphase powders by the co-precipitation method, and homogeneous Al2O3-Ce:LuAG CPCs (the uniform volume fraction between Al2O3 and Ce:LuAG phases) were obtained by vacuum sintering (1775 °C × 10 h). With an increase in the Al3+ content, the morphology of the multiphase powders changes from small irregular shapes to porous flocs and flakes interwoven, and Lu3Al5O12 phases tend to convert to LuAlO3 phases. When the Al2O3 content is 78–89 mol% in the CPCs, the average grain sizes of Al2O3 are close to those of Ce:LuAG. Among all CPCs with an Al2O3 content of 68–95 mol%, the 85 mol% Al2O3-Ce:LuAG CPCs initially perform the best in terms of both excitation and emission intensity at room temperature, and their photoluminescence intensities only decrease 4.3% from 25 to 225 °C. A solid-state laser lighting device was constructed by using a 450 nm laser source and Al2O3-Ce:LuAG CPCs in a reflection mode. The CPCs with 85 mol% Al2O3 content based on 0.9 W laser diodes (LDs) show the optimum luminous flux (LF) and luminous efficiency (LE) of 244 lm and 266 lm∙W−1, respectively. Additionally, the LF of all CPCs based on LDs continues to increase without showing luminescence saturation when the power density increases from 1 to 20 W mm−2. When the 85 mol% Al2O3-containing CPCs are excited by a 20 W mm−2 LD, the maximum LF reaches 3624 lm, and the LE decreases only by 12.4% (compared to the data under 1 W mm−2 excitation). Al2O3-Ce:LuAG CPCs have excellent luminescence properties and improved thermal stability, which are promising for the application in solid-state laser lighting.

Luminescence and thermal stability of CaLu2-x-yMeyMg2Si3O12:xCe3+ (Me = Sr, Ba) fluorescent materials

White light solid-state lighting applications still face significant challenges due to insufficient efficient and stable red light emitting materials. Therefore, a series of orange-red fluorescent materials, CaLu2-xMg2Si3O12:xCe3+ (CLMS:xCe3+; x = 0.02, 0.04, 0.06, 0.08, 0.10, 0.12) were prepared in this paper. Luminescence spectra testing revealed that the optimal concentration of Ce3+ ions in the crystal lattice is x = 0.04. At 460 nm excitation, the emission wavelength is approximately 592 nm. To enhance the thermal stability and luminescence performance of CLMS:Ce3+, the CaLu1.96-yMeyMg2Si3O12:0.04Ce3+ (Me = Sr, Ba; y = 0, 0.02, 0.05, 0.10, 0.15, 0.20) fluorescent materials were successfully prepared. It was found that phosphor's fluorescence intensity was enhanced after the introduction of Sr2+ or Ba2+ ions. Meanwhile, the phosphors were tested for thermal stability, and the emission intensities of CLMS:0.04Ce3+, CLMS:0.04Ce3+,0.10Sr2+, and CLMS:0.04Ce3+,0.05Ba2+ phosphors decreased to 77.60%, 85.53%, and 87.63% at 423 K, respectively. This proves that Sr2+ and Ba2+ ions have a positive effect on the thermal stability performance of CLMS:0.04Ce3+ phosphor. Testing of the w-LED devices, the CCT was reduced. The CRI was improved to 80.4 and 81.6 and luminescence efficiency was improved to 107.71 lm/W and 115.04 lm/W after Sr2+ or Ba2+ ions were introduced. In summary, this study demonstrates that CaLu2-x-yMeyMg2Si3O12:xCe3+ (Me = Sr, Ba) is an auspicious fluorescent material with high thermal stability, which is potentially informative for the field of white-light illumination.