Luminescence Performance Research Articles

Modification in structural, electrical and defect luminescence properties of ZnO nanorod films with Cu, Al and double-doping

Zinc oxide nanorods have broad application prospects in the field of photoelectric devices. However, the application as photodetectors in the visible light band is limited by their narrow luminescent spectrum and poor electrical conductivity. In this work, three different zinc oxide nanorod films respectively with Cu, Al and double-doping have been prepared for investigating the modifying effect of their defect luminescence and electric performance. In this paper, Cu doped zinc oxide with rod structure and Al doped zinc oxide with flaky structure are fabricated by hydrothermal method and sol-gel method, respectively. As for the double-doping, Al doped zinc oxide films are grown on the surface of Si by sol-gel method, and Cu doped zinc oxide nanorods are grown on the surface of Al doped zinc oxide films by hydrothermal method. The results show that the Cu doping can improve the number of defects, leading to the electrons transport from VZn to Zni and then releasing the photons. Alternatively, the trivalent aluminum ions exist in zinc oxide nanorods in the form of replacement or gap, increasing the carrier concentration, turn-on voltage and rectification ratio of zinc oxides. As for the Cu–Al double-doping, Al doped zinc oxide films are located between Cu doped zinc oxide nanorods and Si substrate and work as an intermediate layer of current. Trivalent aluminum ions can change the semiconductor properties of zinc oxide and make it have the performance of p-type semiconductor which can improve the electrical properties of zinc oxide semiconductor. Besides, the carrier concentration of Cu–Al double-doping zinc oxide is nearly 3 times higher than that of pure one. Increasing the carrier concentration can increase the current of ZnO–Si heterojunction in the dark, thus improving the photoelectric properties of ZnO nanorods.

Synthesis and warm white emission performance of single-component Ca7Mg2(PO4)6:Dy3+, Eu3+ phosphor for white light-emitting diodes

A single-component Ca7Mg2(PO4)6:Dy3+, Eu3+ white-emitting phosphor was synthesized by a sol-gel approach. The effects of the amounts of Dy3+ ions and Eu3+ ions on the luminescence characteristics and crystal structure of Ca7Mg2(PO4)6:Dy3+, Eu3+ were systematically investigated. The Ca7Mg2(PO4)6:Dy3+, Eu3+ phosphors had a Ca7Mg2(PO4)6 structure with an R3c (161) space group. The Ca7Mg2(PO4)6:Dy3+ phosphor showed emission peaks at both 484 nm (blue) and 576 nm (yellow), which led to the realization of white light. Furthermore, after codoping Eu3+ ions into the structure, a red emission peak (∼617 nm) appeared in the spectrum as a supplementary red component. A warm white light with a low correlated colour temperature (CCT) is obtained from Dy3+/Eu3+-codoped Ca7Mg2(PO4)6. The luminescence intensity at 483 K still reaches more than 73 % of that at 303 K. The packaged LEDs display a bright warm white light with CCT value and colour rendering index (CRI) of 3878 K and 86.7, respectively, which is comfortable for the human eye. With excellent luminescence performances, the white-emitting Ca7Mg2(PO4)6:Dy3+, Eu3+ phosphor had a significant application potential in the w-LED field.

The Combination of Upconversion Nanoparticles and Perovskite Quantum Dots with Temperature-Dependent Emission Colors for Dual-Mode Anti-Counterfeiting Applications.

Novel and high-security anti-counterfeiting technology has always been the focus of attention and research. This work proposes a nanocomposite combination of upconversion nanoparticles (UCNPs) and perovskite quantum dots (PeQDs) to achieve color-adjustable dual-mode luminescence anti-counterfeiting. Firstly, a series of NaGdF4: Yb/Tm UCNPs with different sizes were synthesized, and their thermal-enhanced upconversion luminescence performances were investigated. The upconversion luminescence (UCL) intensity of the samples increases with rising temperature, and the UCL thermal enhancement factor rises as the particle size decreases. This intriguing thermal enhancement phenomenon can be attributed to the mitigation of surface luminescence quenching. Furthermore, CsPbBr3 PeQDs were well adhered to the surfaces and surroundings of the UCNPs. Leveraging energy transfer and the contrasting temperature responses of UCNPs and PeQDs, this nanocomposite was utilized as a dual-mode thermochromic anti-counterfeiting system. As the temperature increases, the color of the composite changes from green to pink under 980 nm excitation, while it displays green to non-luminescence under 365 nm excitation. This new anti-counterfeiting material, with its high security and convenience, has great potential in anti-counterfeiting applications.

Effect of the local environment on the luminescence of Er3+/Yb3+-doped aluminate upconversion phosphors

In recent years, trivalent rare-earth ion (RE3+) doped upconversion luminescent (UCL) materials have been studied extensively owing to their potential applications. The structure of the material is the main factor affecting the UCL performance. In this study, three structurally identical Er3+/Yb3+ co-doped aluminates CaYAlO4, CaGdAlO4, and CaLaAlO4 (CYA, CGA, and CLA) phosphors were synthesized, and the effects of the local environment on the UCL performance of Er3+ ions were investigated. The morphology and phonon energy of the samples were not the main factors affecting the luminescence performance in the same structural material. The difference in the crystal field strength was the main reason for the difference in the UCL of the three phosphors, which was attributed mainly to the difference in the crystal field strength and the difference in the degree of distortion of the Al–O octahedra that changes the transition probabilities of the parity forbidden intra-4fN–4fN electronic transitions of Er3+. A comparison of the distances between the RE3+ and the lifetimes of the 4I11/2 and 4I13/2 energy levels in the three materials showed that the red–green ratio of the materials was affected by the energy transfer. Finally, an analysis of the changes in the energy band structure and density of states (DOS) distribution before and after Er3+/Yb3+ doping of CYA, CGA, and CLA found that the effect of the bandgap on the UCL can be neglected when the bandgap of the matrix is larger than the energy difference from the 4I15/2 energy level to the 2H11/2 energy level of the Er3+ ion.

A Photoactivatable Luminescent Motif through Ring-Flipping Isomerization for Multiple Photopatterning.

Photoactivatable luminescent materials have garnered enormous attention in the field of intelligent responsive materials, yet their design and applications remain challenging due to the limited variety of photoactivatable motifs. In the work described herein, we discovered a new photoactivatable luminescent motif that underwent ring-flipping isomerization under UV irradiation. The emission of this motif exhibited a rapid transformation from dark yellow to bright green, accompanied by a significant enhancement of quantum yield from 1.9% to 34.2%. Experimental and theoretical studies revealed that the effective intramolecular motion (EIM) was crucial to the distinct luminescence performance between two isomers. In addition, polymers containing this motif were achieved through a one-pot alkyne polymerization, exhibiting both photofluorochromic and photo-cross-linking properties. Furthermore, multiple types of photopatterning, including luminescent encryption, fluorescent grayscale imaging, and high-resolution photolithographic patterns, were realized. This work developed a new photoactivatable luminescent motif and demonstrated its potential applications in both small molecules and macromolecules, which will help in the future design of photoactivatable luminescent materials.

The Effect of Lu3+ Doping on the Structural Stability and Luminescence Performances of Gd3Al5O12:Dy Phosphors

Transparent ceramics (Gd0.975−xLuxDy0.025)3Al5O12 (x = 0.2, 0.5, 0.975) are fabricated by vacuum sintering with the transmittance of ~60% at 583 nm. The doping of Lu3+ was beneficial to stabilize the garnet phase, and the best doping concentration was 20 at.%. All three (Gd, Lu)3Al5O12:Dy ceramics display typical Dy3+ emission, originating from 4F9/2 → 6HJ (J = 15/2, 13/2, 11/2) transition. Temperature-dependent luminescence spectra from 303.15 K to 603.15 K prove that the (Gd, Lu)3Al5O12:Dy ceramics had good thermal stability and could be an ideal yellow-emitting candidate in light-emitting diodes. The luminous efficiency of the encapsulated white LED lamp was found to be ~87.9 lm/W when the injection current was 600 mA. The transparent (Gd, Lu)3Al5O12:Dy ceramics show great application potential in various optical systems especially in the fields of luminescence and display.

Regulating afterglow of LiGa5O8:Cr3+ for dynamic anti-counterfeiting

Fluorescent materials are widely used in the field of anti-counterfeiting. However, conventional fluorescent materials are limited in anti-counterfeiting applications due to their static mode. Here, LiGa5O8:Cr3+ phosphors were prepared at different calcination temperatures by high-temperature solid-state reaction and further fabricated into dynamic anti-counterfeiting films. Samples can emit red light with main emission peak at 719 nm due to 2E → 4A2 transition of Cr3+ ions. By adjusting calcination temperature from 1300 °C to 1550 °C, red afterglow of the film was controlled with respect to luminescence intensity and duration. In addition, 1450 °C was identified as the optimum calcination temperature to prepare LiGa5O8:Cr3+ phosphors with the best luminescent performance. Based on this control strategy, the application of LiGa5O8:Cr3+ in the field of dynamic anti-counterfeiting can be realized.

808 nm excited multi-color upconversion luminescence and optical temperature sensing through Yb3+-mediated energy transfer in Nd3+-sensitized system

Herein, Na3Y(VO4)2:Nd3+,Yb3+,Ho3+/Er3+/Tm3+ are synthesized through the solid-state reaction method. By utilizing Yb3+-mediated energy transfer in Nd3+-sensitized various activators (Ho3+/Er3+/Tm3+) system, 808 nm excited multi-color upconversion luminescence is realized. Yb3+ plays an important role in energy transfer bridging, and the introduction of Yb3+ in Nd3+-sensitized system can significantly improve emission of activators by nearly two orders of magnitude. The main luminescence mechanism of Nd3+→Yb3+→Activators (Ho3+/Er3+/Tm3+) is proved via measuring the emission characteristics and luminescence decay curves. With efficient upconversion luminescence, the optical thermometry behaviors for Na3Y(VO4)2:Nd3+,Yb3+,Ho3+/Er3+/Tm3+ are investigated. The maximum relative and absolute sensitivities are 1.08 % K−1 and 7.82 × 10−3 K−1 for Na3Y(VO4)2:Nd3+,Yb3+,Er3+; 1.01 % K−1 and 4.22 × 10−3 K−1 for Na3Y(VO4)2:Nd3+,Yb3+,Tm3+; and 1.08 % K−1 and 22 × 10−3 K−1 for Na3Y(VO4)2:Nd3+,Yb3+,Ho3+, respectively. Based on the multi-color upconversion luminescence and high sensitivity thermometry performance, the Na3Y(VO4)2:Nd3+,Yb3+,Ho3+/Er3+/Tm3+ phosphors have potential applications in fields of solid-state display and safety sign of high-temperature.

Investigation of Mechanochromic Luminescence of Pyrene-based Aggregation-Induced Emission Luminogens: Correlation between Molecular Packing and Luminescence Behavior.

To better understand the correlation between molecular structure and optical properties such as aggregation-induced emission (AIE) and mechanochromic luminescence (MCL) emission, two new pyrene-based derivatives with substitutions at the 4- and 5-positions (1HH) and at the 4-, 5-, 9-, and 10-positions (2HH) were designed and synthesized. Cyano groups were introduced at the periphery of the synthesized compounds (1HCN, 1OCN, 1BCN, 2HCN, 2OCN, and 2BCN) to investigate the influence of these groups on the emission properties of the pyrene derivatives both in solution and in the solid state. The fluorescence emission performance of these compounds in water/acetone mixtures was simultaneously studied, revealing outstanding aggregation-induced emission properties. The typical shift in emission maxima to higher values was attributed to J-aggregate formation in the aggregate state. Careful investigation of the crystal structures demonstrated abundant and intense intermolecular interactions, such as C-H…π and C-H…N hydrogen bonds, contributing to the remarkable mechanochromic luminescence performance of these compounds. The MCL properties of all the compounds were investigated using powder X-ray diffraction, and the remarkable mechanochromic properties were attributed to J-aggregate phenomena in the solid state. These results provide valuable insights into the structure-property relationship of organic MCL materials, guiding the design of efficient organic MCL materials.

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.

Peculiar β-Li2TiO3: Eu3+ red light emitting dominated by electric dipole transition: Asymmetric lattice point regulation and luminescence performance

In order to obtain red phosphor with high color purity, β-Li2TiO3: Eu3+ dominated by electric dipole transition was prepared by the hydrothermal method. Eu3+ doping concentration (< 0.5 mol%) and calcination time (> 12 h) can regulate the phase purity, supercell development, asymmetric lattice point configuration and the luminescence performance. Under excitation at 394 nm, β-Li2TiO3: Eu3+ emits narrow band 618 nm red light due to that Eu3+ replaces Li+ at the relatively active Li1 position, and the 5D0 → 7F2 electric dipole transition dominates. Calcined at 600 °C for 36 h with Eu3+ doped concentration of 0.5 mol%, the luminescence performance of β-Li2TiO3: Eu3+ is superior, of which the lifetime is 0.64 ms, the color coordinates x = 0.63, y = 0.37, the color temperature of 987 K, the color rendering index of 82, and the red color purity of 99.7%. The electric dipole transition line intensity parameters Ω2 and Ω4 are 8.01 × 10−20 cm2 and 0.62 × 10−20 cm2, respectively, yielding Ω2/Ω4 of 12.9. The fluorescence branch ratio of 5D0 → 7F2 is 82.9%, and the quantum efficiency can reach 92%, which is superior within similar materials.

Unity emission in organic phosphonium antimony halide for high color rendering white LED

Metal halides have attracted increasing attention in luminescent applications because of their fantastic properties in optoelectronics and easy solution processability. However, toxicity of Pb element and low photoluminescence quantum yield (PLQY) hamper their practical application. Herein, we report a lead-free zero-dimensional antimony (Ⅲ) hybrid halide (EPP)2SbCl5 ⋅CH2Cl2 (EPP = Ethyltriphenylphosphonium), in which inorganic luminescent center [SbCl5]2- are surrounded by organic ligands, forming a perfect host-guest system and exhibiting unprecedented photophysical properties. The (EPP)2SbCl5⋅CH2Cl2 exhibits a bright orange-red emission located at 623 nm, a near-unity PLQY of 97.09 %, and a large Stokes shift of 253 nm. The characterization of photophysical properties shows that broadband emission with microsecond decay lifetime (6.98 μs) is derived from self-trapped exciton emission. Together highly efficient and ultra-stable luminescence performance enable (EPP)2SbCl5⋅CH2Cl2 as excellent down-conversion phosphor to successfully fabricate white light-emitting diodes (LEDs) device with a color rendering index of 95. It is proved that the prepared 0D antimony hybrid halide with ultrabroad-band emission and near-unity PLQY is a promising solid-state lighting luminescent material.

Gd-MOF composites luminescent arrays for highly sensitive detection of epileptic drug and biomarkers

Nowadays, more than 50 million people suffer from epilepsy in worldwide. Epilepsy can be diagnosed more efficiently by detecting epileptic biomarkers such as human serum albumin (HSA) and relative nucleic acid. Pregabalin is an effective curing drug for epilepsy, but the dosage of it needs to be strictly controlled. In this work, to realize highly efficiently detect and discriminate epileptic curing drugs and biomarkers (pregabalin, epilepsy-DNA-1, and HSA), a novel Gd-MOF has been synthesized by H2L ligand (H2L = 5-(4-(imidzol-1-yl)phenyl)isophthalic acid), namely [Gd2L3(DMF)(H2O)2]n, which can be further functionalized with 3-Bromo-L-phenylalanine (L-3-Br-PHE-OH), thioflavin T (ThT) and fluorescein isothiocyanate isomer I labeled anti-HSA (anti-HSA/FITC), respectively. Through the post-synthetic modification (PSM) method, three Gd-MOF composite materials with good luminescence performance can be successfully prepared, namely Gd-MOF@L-3-Br-PHE-OH (Gd-MOF-1), Gd-MOF@ThT (Gd-MOF-2), Gd-MOF@anti-HSA/FITC (Gd-MOF-3). These three composite materials can be used for the detection of pregabalin, epilepsy-DNA-1, and HSA with high selectivity and sensitivity, respectively. The limit of detection (LOD) is 45.41 nM for pregabalin, 5.56 nM for epilepsy-DNA-1, and 5.11 nM for HSA. Development of detection application of Gd-MOF composite materials for drugs and biomarkers was also performed in the real biological samples. Principal component analysis (PCA) and hierarchical cluster analysis (HCA) results demonstrated that Gd-MOF based luminescent array can simultaneously identify and detect epileptic drugs and biomarkers in the human serum environment. Finally, detection mechanisms for this epileptic drug and biomarkers were also investigated and discussed in detail.

Antimony-Triggered Tunable White Light Emission in Lead-Free Zero-Dimensional Indium Halide with Ultrastable CCT of White Light Emitting Diodes.

A highly efficient and easily tunable luminescence is significant for solid-state luminescent (SSL) materials. However, achieving a photoluminescence quantum yield (PLQY) close to unity and tuning the emission remain challenging tasks. Metal doping strategies enable resolution of these issues. Herein, we report the preparation of a novel organic-inorganic lead-free indium-based metal halide hybrid (MP)3InCl6•EtOH (MP = C4H10ON) with a typical zero-dimension structure. When excited at 320 nm, (MP)3InCl6•EtOH exhibits a dual emission band at 420 and 600 nm, which originates from the organic cation [MP] and the [InCl6]3- octahedral unit. The photoluminescence can be significantly enhanced through Sb3+ doping, resulting in an increase in PLQY from 0.78% to near unity. Multiple emission color tunings have been achieved by regulating the Sb doping level and the radiation wavelength, resulting in a change in emission color from blue → white → orange. Optical characterizations reveal that the significantly enhanced emission centered at 600 nm can be attributed to more efficient absorption, closely associated with an additional 1S0 → 3P1 transition in the inorganic octahedron [In(Sb)Cl6]3- due to Sb3+ doping. With its excellent optical performance, a white light emitting diode (WLED) has been successfully fabricated by coating the mixture of (MP)3InCl6•EtOH:15%Sb3+ with blue phosphor BaMgAl10O17:Eu2+ onto a UV LED chip. The WLED device exhibits perfect white light emission with regard to the International Commission on Illumination (CIE) coordinates of (0.36, 0.34). Significantly, the WLED device maintains a stable correlated color temperature (CCT) range of 4119-4393 K and CIE coordinates (x: 0.37-0.34, y: 0.35-0.33) as the driven current varies from 20 to 200 mA, demonstrating outstanding stability across different power levels. This work not only presents a novel system for achieving remarkably enhanced luminescent performance and tuning emission bands in 0D metal halides but also represents a significant step toward achieving resistance to color drifting for stable WLEDs.

Rapid synthesis of ultra-bright blue and cyan CQDs fluorescent powders based on chemical dispersion and concentration effects

It is often impossible to obtain solid carbon quantum dots (CQDs) fluorescent powder by direct drying due to a self-quenching effect, which limits their large-scale application. Here, we first report a general method for rapidly conversing CQDs solution into fluorescent powder via a crosslinking reaction of 3-glycidyloxypropyltrimethoxysilane (KH-560). Initially, N-doped CQDs (N-CQDs) with an ultra-high quantum yield (QY) of 98.45 % and concentration-dependent luminescence behavior were synthesized via a straightforward hydrothermal reaction involving citric acid and ethylenediamine. The N-CQDs solution at low and high concentrations emits blue and cyan fluorescence under ultraviolet light, respectively. By the action of aqueous ammonia, KH-560 quickly forms a gel matrix at room temperature to realize the dispersion and anchor of N-CQDs to prepare N-CQDs fluorescent powder (NK). NK not only inherits the strong luminescence performance (QY = 71.87 %) of N-CQDs but also exhibits excellent fluorescence stability, successfully applied in blue and cyan LED lighting and fluorescent ink.

Defect-management-induced multi-stimulus-responsive mechanoluminescence in Mn2+ doped gallate compound

Exploring mechanoluminescence (ML) materials having multi-stimulus-responsive luminescence is conducive to promoting the development of ML field applications. However, integrating the multi-stimulus-responsive luminescence into a single material is challenging, especially when concerning the unclear multi-stimulus-responsive luminescence mechanisms. Herein, we successfully synthesized a Mn2+-activated broadband multi-stimulus-responsive ML material in a non-centrosymmetric piezoelectric host (LiGaO2: Mn2+). Utilizing the defects’ homology characteristic between ML and persistent/photo-stimulated luminescence, it is confirmed that one can manage the distribution and depth of defects to determine the internal relationship between the multi-stimulus-responsive luminescence and defects. Meanwhile, the V••o and V'Li defects and distribution play a dominant role in multi-mode luminescence. The dynamic process of multi-stimulus-responsive luminescence that charge carriers trapped in deep defects are supplemented to shallow defects can be proved by experimental and DFT calculation results. Based on the excellent multi-stimulus-responsive luminescence performance, the proof-of-concept multi-mode application prospects are demonstrated. This work will deepen our understandings of the multi-stimulus-responsive luminescence mechanism via regulating the distribution and composition of defects to further promote research on flexible X-ray detectors and anti-counterfeiting fields.

Improved performance of polymer light-emitting diodes using graphene oxide doped with silver nanoparticles as the hole-transport layer

This study successfully demonstrates the fabrication of a thin film of graphene oxide doped with silver nanoparticles (GO:AgNPs) using electrochemical exfoliation and photochemical synthesis. The GO:AgNPs thin film exhibits a higher work function and conductivity compared to poly[3,4-ethylenedioxythiophene] polystyrene sulfonate (PEDOT:PSS), making it a promising candidate for the hole-transport layer in polymer light-emitting diodes (PLEDs). Among various configurations, a PLED incorporating GO:AgNPs as the interlayer, which is prepared under blue-light illumination, exhibits optimal luminescent performance. This configuration achieves the highest luminance of 6341 cd/m2 and the highest average current efficiency of 1.87 cd/A. Notably, this novel PLED demonstrates a remarkable 168 % enhancement in average current efficiency and an impressive 637 % increase in electroluminescence intensity compared to a PLED employing a PEDOT:PSS interlayer.

Crystal Field Engineering Yields New 3D Layered Solid Solution Phosphors (Ca/Sr)4MgAl2Si3O14:Eu2+ for White-Light-Emitting Diode Full-Spectrum Lighting.

The cation-equivalent substitution strategy has the ability to manipulate the luminescence color of phosphors and enhance their overall luminescence performance. A series of novel yellow feldspar-type 3D layered phosphors (Ca1-ySry)4MgAl2Si3O14:xEu2+ were synthesized using a high-temperature solid-state reaction. The solid solution phosphors belong to a tetragonal crystal system with a space group of P4̅21m and cell parameters of a = b = 7.75407-7.91794 Å, c = 5.04299-5.22543 Å, and V = 303.166-327.602 Å3. Under near-ultraviolet (n-UV) excitation, the luminescence color of the phosphor undergoes modulation from yellow-green (530 nm) to blue (467 nm) as the Sr2+ ion substitution ratio increases. This modulation is attributed to the gradual decrease in crystal field splitting energy. Additionally, both the Stokes shift and the full width of the luminescence spectra decrease. Furthermore, there is an increase in the quantum yield (QY) from 45.50 to 60.73%. Finally, the fabricated white-light-emitting diode devices emitted warm white light and achieved high Ra (Ra = 94, 96.6, 92.7) and low correlated color temperature (CCT = 3486, 3430, 3788 K), indicating that the prepared solid solution phosphors can be used as candidate materials for WLED lighting.

YAG:Ce films for laser-driven white lighting: Annealing temperature and atmosphere-controlled luminescence performances

The availability and performance of color converters are crucial for the development of laser-driven white lighting. A challenging and important research topic is the discovery of new and efficient color converters. In this work, a color converter, YAG:Ce films as thin as 12.64 µm on thermally conductive single crystal sapphire, was reported. Spray pyrolysis technique was used to deposit YAG:Ce films. The as-deposited films were smooth, semitransparent, and free of macroscopic defects. The quality of YAG:Ce films, which influenced their luminescence performance under high-power-density laser excitation, was controlled by annealing temperature and atmosphere. The best luminescence performance under high-power laser excitation was exhibited by the films annealed at 1500 °C in CO atmosphere. The YAG:Ce film annealed at 1500 °C in the CO atmosphere remained bright yellow, smooth, semitransparent, and free of macroscopic defects, despite being subjected to 1500 °C for 5 h in the CO atmosphere and being as thin as 12.64 µm. The luminous flux and conversion efficiency of YAG:Ce film annealed at 1500 °C in the CO atmosphere were around 2.6 times higher than those of the film annealed at 1500 °C in the air atmosphere under 10 W·mm−2 laser excitation. The saturation threshold of YAG:Ce film annealed at 1500 °C in the CO atmosphere was 9 W·mm−2. This color converter has great potential for advancing laser-driven white lighting technology.

Structural and luminescence performance of the Eu3+ doped alkaline combined metal oxide-based sodium phosphate phosphors; NaMPO4 (M = Mg, Ba, and Ca) for LED applications

The present research module is about the synthesis of Eu3+ ions-doped NaMPO4(M = Mg, Ba, and Ca) phosphate phosphors by the solution combustion synthesis method. The phase formation and chemical structures of alkaline combined metal oxide-based sodium phosphate phosphors are characterised by X-ray powder diffraction (XRD) and FT-IR measurements. Optimized crystal geometries were generated by employing VESTA software. The crystallite size was calculated from the full width at half maximum (FWHM) of the diffraction peak using the Scherrer formula. G-Fourier transformation software (G-FT) was adopted for generating electron density mapping of NaMgPO4 phosphors, 2D mapping, and 3D chicken plots showing crystal sites occupied by the compound’s constituent elements. The particle size distribution was confirmed by XRD diffraction, and SEM analysis found approximately 12 μm. UV–visible and photoluminescence spectroscopy uncover the optical traits of the prepared phosphor. Photo-emissions of Eu3+doped alkaline combined metal oxide-based sodium phosphate phosphors were monitored at possible excitation wavelengths. The orange-red peak observed at 592 nm and 598 nm occurs due to 5D0-7F1 electric dipole transitions. The peak observed at 618 nm corresponds to the forbidden f-f transitions 5D0-7F2. It is worth mentioning that absorption bands originating from the corresponding 5D0-7F2 transition widen the band region; hence, the stark effect becomes complicated. A low-intensity peak of 688 nm was observed in the NaCaPO4 phosphors, attributed to the 5D0-7F3 transition. Chromaticity coordinates and energy level transitions may determine the colour emission materials. The CIE coordinates of NaMPO4:Eu3+phosphors exhibit reddish emission and find application in light-emitting diodes (LEDs) and illuminating displays.