Materials For Solid-state Lighting Research Articles

Controllable Multi-Exciton Zero-Dimensional Antimony-Based Metal Halides for White-light Emission and β-Ray Detection.

Self-trapped exciton (STE) emission, typified by antimony (Sb), with broadband characteristics, represents the next generation of materials for solid-state lighting and radiation detection. However, little is known about the multiexciton behavior of the Sb emission center. Here, we proposed a general approach for designing antimony-centered multi-exciton emitting materials through self-assembly. Benefitting from controllable multiexciton behavior, dual-band white light emission spanning the entire visible spectrum was achieved. Relying on the reduction of an effective atomic number brought by self-assembly, excellent scintillation response to β-rays was attained. This study offers unprecedented insight into hybrid single/triple STE emission and unveils new avenues for single-emitter white-light emission, as well as radiographic testing using low-risk β-rays as sources.

Up-conversion materials for solid-state lighting

AbstractConventional phosphor-converted white LEDs (WLEDs), using (Stokes) down-conversion light emission, suffer from a red deficiency that increases the Color Temperature towards “cool white light” above 5000 K. The present work describes a phosphor-Up-converted WLED approach that wishes to overcome this issue by achieving white light generation (WLG) through Up-conversion photoluminescence (UCPL), without energy losses due to Stokes shift and excited by a 980 nm LED instead of the more expensive blue LEDs. The UC materials include thin films of lanthanide (Ln)-doped aluminosilicate glass multilayers, alternating (Ln)-doped aluminosilicate and titania films in the form of 1-D photonic crystals and Ln ion-implanted materials. Sol-gel (SG) processing has been used as a low-cost high purity processing method to prepare titania, as well as aluminosilicate films containing Er3+, Tm3+ and Yb3+, for WLG and possible application as WLED materials. The total Ln content varied from a high of 22 mol% to as low as 5.8 mol%. The materials prepared have been characterized by UV-Vis-NIR (using a variable angle specular reflection accessory), plus FTIR and UCPL spectroscopies. The UC light emission was analyzed with the help of CIE chromaticity diagrams. Graphical abstract

Synthesis, structure, and luminescence properties of a 0D organic-inorganic cadmium iodide: Combined experimental and theoretical approach

Hybrid organic-inorganic metal halide materials with zero-dimensional (0D) structures have emerged as a captivating field of research due to their distinctive electronic properties and remarkable broadband emission characteristics. In this study, we successfully synthesized a novel hybrid cadmium iodide compound, (BZA)2CdI4.H2O (BZA+: benzylammonium), in the form of single crystals employing the solvent-evaporation method. The room temperature single-crystal X-ray diffraction analysis revealed that (BZA)2CdI4.H2O possesses a typical 0D crystal structure, where (CdI4)2− anions are spatially isolated and surrounded by (BZA)+ cations and H2O molecules. The crystal packing is intricately governed by various non-covalent intermolecular interactions, including π–π stacking interactions, NH…I, NH…O, and OH…I hydrogen bonds, quantified through Hirshfeld surface analysis. Thermal analysis further demonstrated that the removal of water molecules in the crystal lattice yields a dehydrated phase of (BZA)2(CdI4). Upon 330 nm irradiation, the title compound displayed a broad bluish-white light emission, featuring a primary band at 430 nm and a secondary band at 500 nm. Based on photoluminescence spectra measurements and density functional theory (DFT) calculations, the dual-band emission is assigned to the emission of (BZA)+ organic cations and to excitons confined in the [CdI4]2– isolated inorganic tetrahedron, respectively. Interestingly, the presence of isolated molecular units in the 0-D structure results in strongly localized charges and bluish-white light emission with Commission International de l'Eclairage (CIE) colour coordinates (0.23, 0.28). These results confirm the promise of 0D metal-halide hybrids with dual-band emission as luminescent materials for solid-state lighting.

Self-Trapped Exciton Emission Enhancement in 3D Cationic Lead Halide Hybrids Via Phase Transition Engineering.

Three-dimensional (3D) cationic lead halide hybrids constructed by organic ions and inorganic networks via coordination bonds are a promising material for solid-state lighting due to their exceptional environmental stability and broad-spectrum emission. Nevertheless, their fluorescence properties are hindered by the limited lattice distortion from extensive connectivity within the inorganic network. Here, a dramatic 100-fold enhancement of self-trapped exciton (STE) emission is achieved in 3D hybrid material [Pb2Br2][O2C(CH2)4CO2] via pressure-triggered phase transition. Notably, pressure-treated material exhibits a 110 nm redshift with 1.5-fold enhancement compared to the initial state after pressure was completely released. The irreversible structural phase transition intensifies the [PbBr3O3] octahedral distortion, which is highly responsible for the optimization of quenched emission. These findings present a promising strategy for improving the optical properties of 3D halide hybrids with relatively high stability and thus facilitate their practical applications by pressure-driven phase transition engineering.

Full-Spectrum White-Light Emission from Triple Self-Trapped Excitons in Hybrid Mixed-Metal Halides.

Low-dimensional metal halides with broadband emissions are expected to serve as downconversion luminescent materials for solid-state lighting (SSL). However, efficiently generating full-spectrum white-light emission with a high color-rendering index (CRI) in single-phase emitters remains a challenge. Here, we report a novel zero-dimensional (0D) hybrid mixed-metal halide (TPA)2CuAgI4 (TPA = tetrapropylammonium), in which individual [CuAgI4]2- dimers are completely isolated and surrounded by the organic cations TPA+. Cu+ and Ag+ share the same crystallographic site in [CuAgI4]2- dimers with the same statistical probability. Upon photoexcitation, single crystals exhibit a full-spectrum white-light emission with a full width at half-maximum (fwhm) of up to 314 nm and a high quantum efficiency of 46.8%. Detailed photophysical studies and theoretical calculations reveal that the ultra-broadband emission of (TPA)2CuAgI4 originates from the radiative recombination of red-, green-, and blue-emitting self-trapped excitons in [CuAgI4]2- dimers. In addition, (TPA)2CuAgI4 nanocrystals were successfully synthesized and exhibited optical properties similar to those of single-crystal counterparts. Finally, a prototype ultraviolet (UV)-pumped white-light-emitting diode (WLED) and a composite thin film employing this new white-light emitter produces a well-distributed full-spectrum white light with a high CRI of 91.4 and a warm correlated color temperature (CCT) of 4135 K, indicating the potential application of this white-light emitter in SSL. These results provide a new perspective for designing superior single-phase white-light emitters.

Ligand Steric Profile Tunes the Reactivity of Indium Phosphide Clusters.

Indium phosphide quantum dots have become an industrially relevant material for solid-state lighting and wide color gamut displays. The synthesis of indium phosphide quantum dots from indium carboxylates and tris(trimethylsilyl)phosphine (P(SiMe3)3) is understood to proceed through the formation of magic-sized clusters, with In37P20(O2CR)51 being the key isolable intermediate. The reactivity of the In37P20(O2CR)51 cluster is a vital parameter in controlling the conversion to quantum dots. Herein, we report structural perturbations of In37P20(O2CR)51 clusters induced by tuning the steric properties of a series of substituted phenylacetate ligands. This approach allows for control over reactivity with P(SiMe3)3, where meta-substituents enhance the susceptibility to ligand displacement, and para-substituents hinder phosphine diffusion to the core. Thermolysis studies show that with complete cluster dissolution, steric profile can modulate the nucleation period, resulting in a nanocrystal size dependence on ligand steric profile. The enhanced stability from ligand engineering also allows for the isolation and structural characterization by single-crystal X-ray diffraction of a new III-V magic-sized cluster with the formula In26P13(O2CR)39. This intermediate precedes the In37P20(O2CR)51 cluster on the InP QD reaction coordinate. The physical and electronic structure of this cluster are analyzed, providing new insight into previously unrecognized relationships between II-VI and III-V materials and the discrete growth of III-V cluster intermediates.

A green light emissive LaSr2AlO5:Er3+ nanocrystalline material for solid state lighting: crystal phase refinement and down-conversion photoluminescence with high thermal stability.

The present study reveals the structural and optoelectronic characteristics of a down-converted (DC) green luminous Er3+ doped LaSr2AlO5 phosphor that was produced by employing an efficient and reliable gel-combustion process assisted with urea as a fuel. Using Rietveld refinement of diffraction data, the crystal structure and phase formation were examined. The surface morphology and elemental configuration of the phosphor were analyzed via TEM and EDX spectroscopy, respectively. The band gap of LaSr2AlO5 (5.97 eV) and optimized La0.96Sr2AlO5:4 mol% Er3+ (5.51 eV) classify the optimized sample as a direct band-gap material. The PL peaks located in the visible range corresponding to transitions 2H9/2 → 4I15/2 (406 nm), 2H11/2 → 4I15/2 (520 nm), 4S3/2 → 4I15/2 (550 nm), and 4F9/ 2 → 4I15/2 (665 nm) were revealed by photoluminescence spectroscopy under 377 nm excitation. Above 4 mol% Er3+ doping, concentration quenching was observed, which was controlled by the quadrupole-quadrupole interaction. Based on the findings of the double exponential fitting of lifetime curves acquired from the emission spectra at λex = 377 nm and λem = 550 nm, the average lifetime of the excited levels of considered nanomaterials was estimated. The temperature-dependent emission spectra of the La0.96Sr2AlO5:4 mol% Er3+ sample were collected in the range 298-498 K. The considered phosphor was found to have a high thermal stability as evidenced by the luminous intensity being sustained at 74.29% at 498 K compared to the intensity at ambient temperature (298 K) with an activation energy of 0.1453 eV. The calculated color purity and superb chromaticity coordinates indicates that the phosphors have a high degree of color purity, which further supports its applicability as a green component in solid-state lighting.

Two new rare-earth oxyborates Ba4BiTbO(BO3)4 and Ba1.54Sr2.46BiTbO(BO3)4 and luminescence properties of the Ba4BiTb1-xEuxO(BO3)4 phosphors.

Single crystals of two new terbium oxyborates Ba4BiTbO(BO3)4 and Ba1.54Sr2.46BiTbO(BO3)4 were obtained by the high-temperature solution method. They crystallize in the hexagonal P63/mmc group (Z = 2) with lattice parameters of a = 5.41865(9) Å, c = 26.3535(5) Å, V = 670.12(3) Å3 and a = 5.36534(19) Å, c = 26.0661(10) Å, V = 649.83(5) Å3, respectively. Their crystal structures feature two kinds of layers: [Tb(BO3)2]n3n- formed by corner-sharing TbO6 octahedra and BO3 triangles, as well as [Bi(BO3)2O]n5n- consisting of Bi2O13 dimers and BO3 groups, with alkali-earth cations sitting inside and between the layers. In addition, solid solutions of Ba4BiTb1-xEuxO(BO3)4 (0 ≤ x ≤ 0.2) were prepared via the solid-state reaction method. The obtained products were characterized by powder XRD, SEM, IR/Raman, XPS, DRS, and luminescence spectroscopy. It was found that as the Eu3+ doped content varies from x = 0 to 0.2, the emission color of the Ba4BiTb1-xEuxO(BO3)4 phosphors can be adjusted from cyan to near-white and then to orange-red or from green to orange and then to red under the excitation of 349 and 377 nm, respectively. Furthermore, the emission intensities and chromaticity coordinates were found to be sensitive to the temperature for the phosphor Ba4BiTb0.999Eu0.001O(BO3)4 upon 377 nm excitation. The above results demonstrate that Ba4BiTb1-xEuxO(BO3)4 phosphors have potential as multifunctional materials for solid-state lighting and temperature sensing applications.

Structural and luminescence properties of novel Eu3+-doped Na3Ba2LaNb10O30 phosphors with high quantum efficiency and excellent color purity for w-LED applications.

In this study, we report the successful synthesis and thorough characterization of Eu3+-doped Na3Ba2LaNb10O30 phosphors, targeting their application in white-light-emitting diodes (w-LEDs). The phosphors were synthesized using a high-temperature solid-state method, ensuring robust incorporation of Eu3+ ions into the host lattice. Comprehensive analyses were performed, including X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray (EDX) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy and Raman spectroscopy, confirming the phase purity, crystallinity, morphology, and elemental composition of the phosphors. We have also studied the electronic structure using diffuse reflectance spectroscopy (DRS). Photoluminescence studies revealed strong red emissions under near-ultraviolet light excitation, with the optimal Eu3+ doping concentration identified to be 9 mol%. Quantum-yield measurements demonstrated high luminescence efficiency, while chromaticity coordinates indicated excellent color purity suitable for w-LED applications. These findings contribute significantly to the advancement of phosphor materials for solid-state lighting, suggesting promising prospects for their integration into commercial LED devices.

N-UV triggered green emitting Er3+ doped Zirconia: A bifunctional material for solid-state lighting and optical thermometry

In the current piece of work, we have synthesized the Er3+-activated ZrO2 and illustrated the bifunctional utility of this material for solid-state lighting and non-contact optical thermometry. The synthesized samples were characterized by XRD, XPS, and PL techniques for their structural, surface, and luminescence studies. Under the excitation of 377 nm, characteristic green emission corresponding to intra 4f-4f transitions of Er3+ is obtained. The concentration quenching effect was observed beyond 1.2 mol % concentration of doping. Using Dexter's theory, it was revealed that dipole-quadrupole interactions are predominantly responsible for concentration quenching. The Photometric study was performed using the PL data. For the most intense phosphor, a highly pure green color (color purity ∼ 97.6%) and CCT ∼ 5375 K is observed. Furthermore, the temperature-sensing capability of the most intense sample has also been explored by triggering the synthesized phosphor by n-UV light. The temperature sensing performance is checked by measuring variations in the fluorescence intensity ratio (FIR) of the thermally coupled levels of Er3+ with temperature. The synthesized phosphor gives high relative sensitivity (1.19% K−1 at 303 K)) and absolute sensitivity (11.39 × 10−4 at 603 K)) values. These results suggest that n-UV-triggered Er3+ doped ZrO2 can be a promising bifunctional material for applications in solid-state lighting and non-contact optical thermometry.

Physicochemical Characterization of the Hybrid Molybdate–Tungstate Materials for Solid-State Lighting

Physicochemical Characterization of the Hybrid Molybdate–Tungstate Materials for Solid-State Lighting

Hydrothermal synthesis of defect-induced pristine α-NaCe(WO4)2: a novel material for solid state lighting and gas sensing

Triclinic NaCe(WO4)2 with oxygen monovacancies and divacancies has been successfully prepared via a facile cetyltrimethyl ammonium bromide (CTAB)-assisted hydrothermal technique.

Realizing near white and warm light emission of cuprous iodide complexes by alkyl-isomerization of ligands.

Four novel all-in-one structured cuprous iodide hybrid materials are presented. Isomerization of the alkyl chain on the ligand improved material thermal stability and regulated their luminescence to warm and near-white light emission, with the internal quantum yield increasing from 5% to 83%. This provides a reasonable route for designing white light emitting cuprous iodide materials for solid-state lighting in future.

Insight into luminescence properties of Li+ co-doped Sr2SnO4:Eu3+ phosphors by co-precipitation assisted hydrothermal synthesis

Sr2SnO4:Eu3+ phosphors were prepared by a co-precipitation combined with hydrothermal method for the first time, and Li+ was introduced to improve its luminescence performance. X-ray diffraction analysis determined that Sr2SnO4:Eu3+, Li+ phosphors were successfully synthesized. The effects and mechanisms of Li+ doping on the luminescence properties of Sr2SnO4:Eu3+ were specifically discussed. At 260 nm excitation, the fluorescence spectra of the products were dominated by the 5D0-7F1 characteristic emission peak of Eu3+ at 598 nm, with the electric dipole transition 5D0-7F2 being distinctly lower than the magnetic dipole transition 5D0-7F1, indicating that Eu3+ selectively replaced the highly symmetrical defective sites of Sn4+. The luminous intensity and decay lifetime were significantly enhanced through co-doping Li+, which played an essential role as a charge compensator. The optimum doping concentration of Li+ was 7%. Finally, the color purity of Sr2SnO4:Eu3+, Li+ reached 99.9%, suggesting that it could be developed as a potential orange-emitting material for solid-state lighting.

Sm3+ ions doped Sm2Si2O7-based glass ceramics: Crystallization, luminescence and energy transfer process through heat treatment

Sm3+ ions incorporated Sm2Si2O7 crystalline phase formed in the aluminoborosilicate glass matrix synthesized via melting quenching technique followed by heat-treatment process is reported herewith. The preliminary confirmation on the obtained glass ceramics was made through X-ray diffration (XRD) studies. Formation of non-bridging oxygens (NBOs) in the glass network and the modes of vibrations of network units were analyzed through Fourier transform infrared spectroscopy (FTIR) studies. Surface morphology of heat-treated samples at varying temperatures was determined via a field emission scanning electron microscope (FESEM). The absorption studies on heat-treated samples signify the low bandgap values and high Urbach energy values due to improved crystallinity in the glass network. Judd–Ofelt intensity parameters identified for visible absorption transitions follow the trend of Ω4 >Ω2>Ω6. Excitation and emission studies on heat-treated samples show improvement in their intensities compared to the unheated base glass. The thermal quenching is observed at higher temperatures (540 and 580 °C for 3 h) of heat-treated samples. Calculations based on luminescence spectra including radiative transition probability, stimulated emission cross-section and branching ratio show good results for glass ceramics prior to precursor glass. Longer lifetimes of Sm3+ ions (milliseconds) in the level 4G5/2 are seen for glass ceramics. Color coordinates suggest the reddish-orange emissions from prepared glass ceramics. Thus, Sm3+ doped Sm2Si2O7 glass ceramics are favorable materials for solid-state lighting and laser applications.

Structural and optical characterization of trivalent samarium-activated LaAlO3 nanocrystalline materials for solid-state lighting

This article reports preparation, optical and structural characteristics of LaAlO3:Sm3+nanophosphors. The Gel-combustion method was employed to synthesize the selected phosphor utilizing urea as organic fuel and for further investigation samples were calcined at 800 and 1000 °C. The crystal structure of the considered phosphor was examined by the X-rays diffraction and Rietveld refinement study which confirmed the preparation of cubic unit cell having space group Pm3̅m. Confirmation of smooth morphology of LaAlO3:Sm3+ and estimation of particle size (35–60 nm) has been carried out using Transmission electron microscope (TEM) images. Vibrational behavior of processed nanophosphors was studied by Fourier transform infrared spectroscopy (FTIR) analysis. The synthesis of the desired nanophosphor was confirmed by Energy-dispersive X-ray analysis. The photoluminescence properties were analyzed in detail through measurements of the emission spectrum. The strongest emission detected on 598 nm owing to 4G5/2 → 6H7/2 is liable for reddish-orange emission. These detailed photoluminescent and structural investigation support the expedient utility of LaAlO3:Sm3+ nanophosphor for solid-state lighting purposes.

Tailoring Photophysical Dynamics in a Hybrid Gallium-Bismuth Heterometallic Halide by Transferring from an Indirect to a Direct Band Structure.

Low-dimensional lead-free metal halides have emerged as novel luminous materials for solid-state lighting, remote thermal imaging, X-ray scintillation, and anticounterfeiting labeling applications. However, the influence of band structure on the intriguing optical property has rarely been explored, especially for low-dimensional hybrid heterometallic halides. In this study, we have developed a lead-free zero-dimensional gallium-bismuth hybrid heterometallic halide, A8(GaCl4)4(BiCl6)4 (A = C8H22N2), that is photoluminescence (PL)-inert because of its indirect-band-gap character. Upon rational composition engineering, parity-forbidden transitions associated with the indirect band gap have been broken by replacing partial Ga3+ with Sb3+, which contains an active outer-shell 5s2 lone pair, resulting in a transition from an indirect to a direct band gap. As a result, broadband yellow PL centered at 580 nm with a large Stokes shift over 200 nm is recorded. Such an emission is attributed to the radiative recombination of an allowed direct transition from triplet 3P1 states of Sb3+ based on experimental characterizations and theoretical calculations. This study provides not only important insights into the effect of the band structure on the photophysical properties but a guidance for the design of new hybrid heterometallic halides for optoelectronic applications.

Ultrasensitive Pressure-Induced Optical Materials: Europium-Doped Hafnium Silicates with a Khibinskite Structure for Optical Pressure Sensors and WLEDs.

Ultrasensitive pressure-induced optical materials are of great importance owing to their potential applications in optical pressure sensors. However, the lack of outstanding pressure sensitivity, observable color evolution, and structure reliability limits their further development in both practical applications and luminescence theory. To overcome the above problems, an enlightening methodology is proposed to explore the high sensitivity and phase stability of hafnium silicate K2HfSi2O7 (KHSO) phosphor with a Khibinskite structure. By employing X-ray diffraction (XRD) Rietveld refinement, cryogenic spectroscopy, and ancillary calculations, information on Eu2+ ion occupation is completely obtained at atmospheric pressure. The remarkable pressure sensitivity (dλ/dP = 3.25 nm/GPa-1) and excellent phase stability up to 20 GPa, along with the reproducible color hue variation, exhibit unprecedented superiority when used in optical pressure sensors. These advantages can be assigned to the pressure-induced Eu2+-selective occupation and the unique properties of 5d-4f transition (Stokes shift, nephelauxetic effect, and intense crystal field strength), which are clearly proved by measuring the XRD patterns, Raman spectra, and Gaussian fitting spectra under compression and decompression processes. The excellent luminescence property manifests that KHSO/Eu2+ can be considered as a potential luminescent material for solid-state lighting and optical pressure sensors.

Optical absorption and photoluminescence investigations Dy3+ doped oxyfluoride phosphate glass system for active laser medium and solid-state lighting materials

This article reports on the optical, photoluminescence, and radiative properties of Dy3+ doped oxyfluoride glass. The composition of glass is: 20Li2O–10AlF3–69P2O5–1Dy2O3 (LAPD). The glass has been prepared using the melt-quenching technique at 1100°C with a total mass of 15 grams in an alumina crucible. Judd–Ofelt analysis was used to determine the intensity parameters and radiative properties of Dy3+ ion in glass. The CIE 1931 chromaticity diagram coordinate is calculated to define the color coordinate of emission in a glass sample. Based on research, it is expected to produce glass material that is applied as an active laser medium and solid-state lighting materials.

Effect of Nd2O3 doping on spectroscopic characteristics of zinc barium boro-tellurite glass for laser medium application

The ZnO-BaO-B2O3-TeO2 (ZBBoT) glass samples were prepared, and their properties affected by varied concentrations of Nd2O3 doped in were investigated. The traditional melt quenching process was conducted to synthesize the samples which were explored to identify their density, molar volume, refractive index, absorption, photoluminescence (PL) and PL decay spectral profiles. The optical absorption has been used to derive the Judd-Ofelt (J-O) parameters (Ωλ, λ = 2, 4 and 6). The trend of J-O parameter is Ω2 > Ω6 > Ω4. Moreover, the J-O parameters are used to predict the radiative properties which are significant for the assessment of the suitability of a glass for laser emission. The emission of glasses exhibited 2 peaks at 1060, and 1345 nm. Based on research, it is expected to produce glass material that is applied as an active laser medium and solid-state lighting materials.