Electric Multipole Interaction Research Articles

Highly thermally stable SrLaMgTaO6: Cr3+ double-perovskite phosphors for night-vision applications

In this study, a novel thermally stability broad-band near-infrared (NIR) phosphor SrLaMgTaO6 (SLMT): Cr3+ was research, along with investigations into its structure, morphology, PL spectra and crystal field strengths. Additionally, the mechanism of concentration quenching in these samples was investigated, which primarily attributed to electric multipolar interactions notably. Surprisingly, the NIR emission intensity at 423 K remains 80.4 % of its room temperature intensity, which shows its outstanding thermal stability. To comprehend the mechanism behind the exceptional thermal stability of luminescence, a comprehensive analysis in this material was conducted, focusing on factors such as the crystal field strength of the host material and the electron-phonon coupling (EPC) effect. Subsequently, an optimized phosphor coating was applied to a 470 nm LED chip to get a NIR pc-LED device, which was evaluated for its performance. The research demonstrate that SLMT: Cr3+ phosphor is a promising NIR pc-LED.

Multifunctional Characteristics of BCTH:0.5% Sm3+ Ceramics Prepared via Hydrothermal Method and Powder Injection Molding

Briefly, 0.005-mol Sm3+-doped (Ba0.85Ca0.15)(Ti0.9Hf0.1)O3 ([(Ba0.85Ca0.15)0.995Sm0.005](Ti0.9Hf0.1)O3, BCTH:0.005Sm3+) lead-free ceramics were prepared via hydrothermal method and powder injection molding using paraffin and oleic acid as binders, and the effects of preparation method and sintering conditions on microstructure, dielectric behavior and optical properties were investigated. XRD Rietveld refinement reveals the coexistence of orthogonal, rhombohedral and tetragonal phases, in which the crystal structure and phase fraction are influenced greatly by sintering temperature and holding time. The ceramics present enhanced relaxor behavior and frequency dispersion phenomenon as compared with those prepared by the solid-state sintering method, and the diffusive index γ value is within 1.421–1.673. The transition mechanism and luminescence performance of BCTH:0.005 Sm3+ were analyzed by Blasse formula, photoluminescence spectrum and fluorescence lifetimes, where emission peaks show slight blueshift, fluorescence decay lifetime becomes shorter, electric multipole interaction dominates the energy transfer mechanism, and the down-conversion luminescence is one-photon absorption process. The CIE chromaticity color coordinate (0.4746, 0.5048), correlated color temperature 3134 K and color purity 93.58% are achieved, which reveals that the BCTH:0.005 Sm3+ ceramics express high quality yellow emission rather than orange-red light of the hydrothermal method synthesized nano-powder, and have potential application in optical field.

Fabrication of highly flexible luminescent films, hydro gels and anti-counterfeiting applications of La2MoO6:Sm3+ phosphors

Fabrication of versatile luminescent materials with remarkable quantum yield holds significant importance across various applications. In this context, a series of (1–11 mol %) Sm3+ activated La2MoO6 nanophosphors (LMO:Sm3+ NPs) has been developed. These nanophosphors, denoted as LMO:Sm3+ NPs, serve as a multifunctional platform with applications spanning white LED technology, flexible displays, hydro-gels, and anti-counterfeiting (AC) measures. These phosphors emit a vibrant orange-red light at 601 nm when excited at 402 nm owing to the Sm3+ ions 4G5/2 → 6H7/2 transition, achieving a high quantum yield of 66.2 %. The optimal doping concentration of Sm3+ ions in the LMO host material is identified as 5 mol %, with concentration quenching primarily attributed to electric multi-polar interaction. Remarkably, the newly fabricated LMO:Sm3+ phosphors exhibit a correlated color temperature (CCT) of 2064 K and maintain excellent color stability. Moreover, a transparent AC film is created using the optimized phosphor and Polydimethylsiloxane (PDMS), offering effective AC capabilities through their orange-red emission when exposed to 365 nm UV light. Notably, these phosphors exhibit sustainability, exceptional flexibility, and foldability, expanding their potential applications in the field of AC. These results underscore the potential of LMO:Sm3+ NPs as highly efficient luminescent platforms, catering to a wide range of applications, including white LED's, flexible display devices, hydro-gels, and AC solutions.

Exploring luminescent color tunability and efficient energy transfer mechanism of a single-phased hexagonal nanophosphor for white light emitting diodes (WLEDs) application

Nowadays, NUV-triggered phosphor-converted white light-emitting diodes (pc-WLEDs) have gained prominence as substantial alternatives to conventional incandescent and fluorescent lamps as a source of illumination. In this study, we have successfully developed a Tm3+ codoped La2O3:Sm3+ nanophosphor and investigated its potential suitability for application in white light-emitting diodes (WLEDs). X-ray diffraction (XRD) analysis was conducted to examine the phase impurity and structural characteristics of the synthesized nanophosphor. The analysis confirmed the formation of a single-phase La2O3 nanophosphor with a hexagonal crystal structure. The FT-IR spectrum of the synthesized nanophosphor exhibited distinct peaks associated with the vibrational frequencies of La-O bonds. The peaks observed in the fingerprint region of the spectrum, indicate the presence of La-O atoms in the nanophosphor. However, the HR-TEM analysis confirmed that the prepared nanophosphor had a polycrystalline nature and the observed particle sizes lay within the nanoscale range. The incorporation of Tm3+ ions into the host matrix led to a reduction in the optical band gap, leading to enhanced emission intensity. The photoluminescence (PL) study reveals that the Tm3+ ion exhibited blue emission upon excitation at 360 nm, whereas the Sm3+ ion emits reddish-orange light when excited at 379 nm and 408 nm, respectively. However, under 325 nm excitation, the nanophosphor exhibited a white emission color that resulted from the blending of colors emitted by both Tm3+ and Sm3+ ions. This unique finding suggests that this nanophosphor has the potential to generate white light specifically under this particular excitation wavelength. The efficient energy transfer between Tm3+ and Sm3+ ions was attributed to the electric multipolar interaction between the nearest neighbor ions, leading to a quenching phenomenon. Furthermore, the photometric analysis revealed that the correlated color temperatures (CCTs) associated with the emitted white light were found to be higher than 4000 K. Thus, based on these characteristics, it can be inferred that the prepared nanophosphor has the potential to be utilized as a cool white-emitting nanophosphor for single-phased WLEDs application.

Achieving perfect white light, color tunability and X-ray scintillation in nanocrystalline La2Hf2O7:Eu3+,Bi3+ by photon energy and doping engineering

Materials which can demonstrate multifunctional lighting efficacy could be boon towards sustainable and developed economy owing to large materials crunch and huge electricity demands. In this work, we have hit three birds with one stone by judicious choice of photon energy and dopant composition engineering in bismuth sensitized Eu3+-doped La2Hf2O7 nanoparticles prepared by a molten salt synthesis method. Bismuth is found to stabilized at both La3+ and Hf4+ sites with Bi@La get excited at high photon energy whereas both Bi@La and Bi@Hf get co-excited at low photon energy to produce perfect amalgam of blue and green Bi3+ emissions upon excitation at 365 nm which couples with Eu3+ red emission and produces white light with (0.31, 0.32) color coordinate. Also, color tunability from violet-blue-purple-pink to orangish red is successfully achieved by efficient Bi3+ → Eu3+ energy transfers via electric multipolar interaction. Density functional theory (DFT) calculations for defect formation energy and density of state (DOS) supported distribution of Bi3+ at both La3+ and Hf4+ sites as well as high feasibility of Bi3+ → Eu3+ energy transfers. Moreover, the La2Hf2O7:0.5%Bi3+,x%Eu3+ NPs demonstrated excellent Eu2+/Eu3+ radioluminescence properties. These characteristics of the La2Hf2O7:0.5%Bi3+,x%Eu3+ NPs described above indicate that these phosphors can be used as potential radioluminescent materials for phosphor converted light emitting diodes and X-ray screen.

Structural and lattice dynamics investigation of double luminescent nanosized hybrid Gd2O3

A series of cubic Yb3+/Eu3+ co-doped Gd2O3 using melamine as a complexing ligand have been prepared by low-temperature treatment at 200 °C. Structural and lattice dynamics have been done using XRD and Raman analysis. Photoluminescence analysis of the co-doped Gd2O3 samples is performed at 220, 275, and 980 nm excitations and the plausible mechanism is discussed in detail. The Eu3+ ions asymmetric ratio is calculated as 2.254 in Yb3+ co-doped Gd2O3 lattice. Luminescence lifetimes oscillate between 3.83 and 739 µs. Spectral parameters and J-O intensity parameters are calculated for all co-doped Gd2O3 NPs. Electric-multipole interaction is the energy transfer mechanism responsible for concentration quenching with a critical distance of 11.45 Å in Gd2O3: Yb3+(20 mol%), Eu3+(5 mol%) nanoparticles (NPs) on 980 nm excitation. The sample emits near-white, blue, and orange-red light emissions and can be utilized for bio-labeling applications. Temperature-dependent studies on Gd2O3: Yb3+ (20 mol%), Eu3+ (5 mol%) NPs are performed in the temperature range of 303–478 K. The developed NPs exhibit paramagnetism with a value of 1.580 emu/g owing to Gd3+ intrinsic magnetic moments.

Anti-thermal quenching behavior of Sm3+ doped SrMoO4 phosphor for new application in temperature sensing

SrMoO4: Sm3+ orange red-emitting phosphors for novel application in temperature measurement were prepared by solid-phase synthesis method. SrMoO4: Sm3+ phosphor with scheelite structure was assigned to tetragonal system and I41/a space group. Sm3+ ions could occupy Sr2+ lattice sites of SrMoO4. SrMoO4: Sm3+ consisted of irregular microparticle with well-crystallized pomegranate seed-like morphology and Sm3+ ions can be evenly distributed in the SrMoO4 matrix. The band gap value of SrMoO4: 1.0%Sm3+ (∼4.228 eV) is less than that of SrMoO4 (∼4.267 eV), which is due to generation of defective energy levels in band gap. The appropriate quenching concentration of Sm3+ was 1.0%, the critical distance is ∼25.57 Å and θ is 7.1, close to 8, which was attributed to dipole−quadrupole interaction type of electric multipolar interaction. SrMoO4:1.0%Sm3+ had excellent thermal stability of the PL peak at 598 nm and 644 nm and anti-thermal quenching property of the PL peak at 530 nm and 563 nm. The activation energy based on the intensity of the PL peak at 598 nm is 0.318 eV. The new dual-model thermometry strategy base on exponential function and modified Boltzmann population distribution would be proposed. SrMoO4:Sm3+ phosphor had the absolute sensitivities of 0.108 K−1 based on exponential function and the relative sensitivities of 0.601% K−1 based on modified Boltzmann population distribution. The excellent anti-thermal quenching and good thermal stability of SrMoO4: Sm3+ phosphors indicate that it has a potential for applications as pc-WLEDs and optical thermometry.

Single- and dual-band emission CaNb2O6:Mn2+: Synthesis and luminescence properties

Now free rare earth ions doped materials have attracted a lot of attention. In this work, CaNb2O6:Mn2+ with a pure phase is synthesized by solid-state method in the reducing atmosphere. The crystal structure and luminescence properties of host (CaNb2O6) and CaNb2O6:Mn2+ are investigated. Host (CaNb2O6) under excitation ultraviolet (UV) light emits blue light. CaNb2O6:Mn2+ can show tunable emission from blue to white. Under excitation 260 nm, blue emission of CaNb2O6:Mn2+ is observed owing to the 4T1(4G) → 6A1(6S) transition of Mn2+. When the excitation wavelength is 314 nm, CaNb2O6:Mn2+ emits white light due to the 4T1(4G) → 6A1(6S) transition of Mn2+ and the 6A1(6S)4T1(4G) → 6A1(6S)6A1(6S) transition in Mn2+ - Mn2+ dimers. We measure the concentration dependent spectra of CaNb2O6:Mn2+ and make sure the optimal Mn2+ doping concentration (∼0.8 mol%). We infer that the concentration quenching mechanism is the electric multipolar interaction between nearest-neighbor ions. Based on the temperature dependent spectra of CaNb2O6:Mn2+, we came to the conclusion that CaNb2O6:Mn2+ has a good thermal stability. We analyze the concentration and thermal quenching mechanisms and explain the luminous mechanism by the Tanabe-Sugano energy level diagram of Mn2+ ion. This research results provide a framework for creating Mn2+-doped luminescent materials.

Downconverted significant luminescence enhancement and structural confinement of a dichromatic nanophosphor for potential applications in NUV-triggered cool pc-WLEDs

Trivalent rare-earth ions activated phosphor-converted near ultraviolet (NUV) triggered white light-emitting diodes (WLEDs) are nowadays being explored as a prominent light source, in the field of lighting. Herein, we prepared a sequence of single-phase Gd2O3:Dy3+,Li+nanophosphor via chemical co-precipitation techniques for the applications in cool pc-WLEDs. To examine the crystal structure, luminescent characteristics, and potential applications of WLEDs, a systematic and comprehensive analysis was conducted. This study extensively investigated the effect of Li+ on the Gd2O3:Dy3+white-emitting nanophosphor. The phase purity and crystal structure of nanophosphors were characterized via powder X-ray diffraction (XRD) analysis. Rietveld refinement clearly quantified that the Gd2O3 host possesses two non-equivalent cationic sites that are coordinated sixfold. The interior morphology and elemental composition were illustrated by high-resolution transmission electron microscopy (HR-TEM) and energy dispersive spectroscopy (EDS). These nanophosphors effectively exhibit dichromatic significant photoluminescence (PL) emission bands of Dy3+ ion for blue and yellow color at 486 and 574 nm, while triggered in the NUV range. The blending of blue and yellow color lights yields a broad spectrum of light that appears white color to the human eye. Besides, it has been observed that the incorporation of Li+ significantly enhances the PL-emission intensity. The critical distance between Gd3+ and Dy3+ was determined, and it showed that the electric multipolar interaction was responsible for the energy transfer quenching mechanism. The colorimetric performance reveals that the CIE coordinates fall within the white region of the color space and that the correlated color temperature (CCT) is substantially higher than 4000 K. The lowest color purity (CP) was found to be 4.0% for x = 2 at.%Li+ ion concentration under excitation wavelength 350 nm. These findings suggest that the prepared nanophosphors are a suitable candidate for application in NUV-triggered cool-WLEDs.

White light luminescence in Dy/Tm co-doped yttria stabilized zirconia single crystals

A series of high quality Dy2O3 and Tm2O3 co-doped yttria stabilized zirconia (YSZ) single crystals was synthesized. These crystals have a single cubic structure, and exhibit the characteristic of Dy3+ (blue and yellow emissions) and Tm3+ (blue emission) under excitation with NUV light. Importantly, the hue can be varied between blue and white by modifying the Tm3+/Dy3+ ratio. The photoluminescence and decay curves are consistent with the existence of resonance-type energy transfer from Tm3+ to Dy3+ ions via an electric multipole interaction mechanism. Maximum luminescence intensity is observed in YSZ doped with 0.50 mol% Tm2O3 and 0.75 mol% Dy2O3, and this sample has CIE coordinates (x = 0.33, y = 0.33) in accordance with those for white chromaticity. Thus, the outstanding luminescence properties of these single crystals suggest potential applications in white light emission devices.

Synthesis and luminescent property of Ce3+-doped NaSrY(BO3)2 efficient blue-emitting phosphor as luminescent thermometer

A series of Ce3+ doped NaSrY(BO3)2 phosphors has been synthesized via a solid-state reaction. Investigations based on XRD analysis attest the formation of high-purity and well-crystallized NaSrY1-xCex(BO3)2 (x = 0–0.12) samples. Structural analysis also revealed the insertion of Ce3+ within the host structure by substitution for the YO6 octahedron. Under 340 nm excitation, NaSrY(BO3)2: Ce3+ phosphors exhibit a broad blue emission band centered at 420 nm with a full width at half maxima of 85 nm at room temperature. The optimized Ce3+ concentration of NaSrY(BO3)2: Ce3+ is 3.0 mol% and the corresponding mechanism is assigned to electric multipolar interaction. With increasing temperature, the emission intensity of optimal NaSrY(BO3)2: 0.03Ce3+ sample decreases to 70% and 35% of room temperature intensity at 373 K and 473 K in a completely reversible manner. The emission intensity of Ce3+ ions shows a linear quenching tendency in the temperature range of 293–473 K, in which the maximum sensitivitty value was calculated to be 0.99%/K at 473 K. Temperature-dependent luminescence properties shows that prepared NaSrY(BO3)2: Ce3+ phosphor will be potential applicable as luminescent thermometer.

Photoluminescence characteristics of Sm3+ doped Na13Sr2Ta2(PO4)9 as new orange-red emitting phosphors

This paper describes the synthesis and properties of a new Sm3+-activated phosphor Na13Sr2(1-x)Ta2(PO4)9:2xSm3+ (x = 0.01–0.12). The crystal structure and the phase purities were characterized, and using scanning electron microscopy (SEM), the morphology was investigated. The emission spectra of as prepared phosphors contain some emitting peaks at 560, 595, 650, and 710 nm. The strongest one is 595 nm, resulting from the Sm3+ 4G5/2→6H7/2 transition. In addition, the optimal Sm3+ concentration was determined to be 9 mol%, and we determined that the critical energy transition distance at which concentration quenching occurs is 2.05 nm, suggesting that it is primarily caused by electric multipole interaction. The achievement of this work is to provide a new orange-red phosphor based on a phosphate host lattice.

Structural features and photoluminescence behaviors of color-temperature tunable (Gd,Y)3Al5O12:Ce3+/Cr3+ phosphors with varying compositions

We designed a chemical coprecipitation method to obtain hollow round precursors with hydrated basic carbonate sulfate structures; these precursors were then thermally treated to yield near-spherical (Gd0.99-xYxCe0.01)3(Al1-yCry)5O12 (x = 0.25‒0.99, y = 0‒0.02) garnet phosphors. With ≥35 at.% Y3+ substitution for Gd3+, relatively stable garnet crystal structures could be obtained. More Y3+ addition led to shrinkage of the unit cell; however, Cr3+ doping caused crystal lattice expansion. The Ce3+ activated phosphor exhibited a strong broad emission band at 500‒700 nm arising from 2D3/2→ 2F5/2,7/2 transitions of Ce3+, while the Cr3+ codoped sample presented three additional red emission bands in the range of 675‒725 nm arrtibuted to 2Eg (2g) →4A2g (4f) transition of Cr3+ and some phonon sidebands. At a constant Ce3+ content of 1 at.%, the Cr3+ emission intensity increased to maximum at 0.5 at.% Cr3+ concentration via efficient energy transfer from Ce3+ to Cr3+, which was attributed to electric multipole interactions such as dipole-quadrupole interactions. A higher particle calcination temperature significantly enhanced the luminescence intensity as well as caused spectral redshifts via correlation-induced enhancement of the crystal field splitting. The color temperature could be tailored in a wide range of ∼5075‒3374 K by controlling both Y3+/Gd3+ ratio and calcination temperature. The Cr3+ addition further shortened the fluorescence lifetime for the 556 nm emission of Ce3+.

Novel and wide-ranging color tuning photoluminescence properties of Tb3+/Eu3+ doped garnet-type Li3Lu3Te2O12 phosphor: Energy transfer and enhanced thermal stability

In order to promote the development of white light emitting diodes (WLEDs) with improved color reproduction, the challenge by discovering novel photoluminescence color tuning phosphors via energy transfer (ET) is essential. However, the mechanism of energy transfer among dopants and its effect on ET efficiency have not been fully understood. Therefore, the photoluminescence color tuning in a variety of matrix structures based on energy transfer always needs to be discussed further. Herein, a series of wide-ranging color tunable Li3Lu3Te2O12 phosphors doped with Tb3+/Eu3+ were synthesized by high-temperature solid-state reaction for the first time. The crystalline structure, morphology and chemical composition of as-prepared phosphors were characterized. The excitation and emission spectra, fluorescence decay curve, and the relationship among emission intensity, doping concentration of dopants and CIE coordinates were investigated in detail. The results indicate that photoluminescence color tuning from green to red was realized by designing the Tb3+→Eu3+ energy transfer in Li3Lu3Te2O12:Tb3+, Eu3+ phosphors. The approximation theory of Reisfeld and the electric multipole interaction theory of Dexter were used to analyze the ET mechanism, which reveals that the dipole-dipole and dipole-quadrupole interaction is responsible for the ET process of Tb3+→Tb3+ and Tb3+→Eu3+. In addition, the thermal stability of the as-prepared phosphors was also revealed. Unforgettably, the samples with reasonable design ratio of Tb3+/Eu3+ exhibits a wider color tuning range, excellent luminescence intensity under n-UV excitation and outstanding thermal stability comparable to commercial Y2O3:Eu3+ phosphor after surface treatment, whose emission intensity at 150 °C exceeds 70% of the initial value. In addition, a prototype WLED device was fabricated with representative phosphor and commercial blue phosphor BaMgAl10O17: Eu2+ (BAM: Eu2+), which emitted warm-white light with great color rendering index (CRI) of 84.8, softer correlated color temperature (CCT) of 3989 K and the chromaticity coordinates of (0.3647,0.3178). All the results suggest that Li3Lu3Te2O12:Tb3+, Eu3+ phosphors can be conducted as potential alternative for near ultraviolet (n-UV) pumped phosphor-converted white light-emitting diodes (pc-WLEDs).

Luminescent performances of Ba9-Ca Al2Si6O24:Eu2+, Mn2+ orthosilicate phosphors along with Ca2+ contents

Optical materials composed of (Ba8.8-p-qCap)Eu0.2MnqAl2Si6O24 (p = 2–4, q = 0–0.2) were prepared via a solid-state reaction at high temperature. The X-ray diffraction patterns of the obtained phosphors were analyzed to index the peak positions. The single-phase phosphors showed a trigonal orthosilicate structure with R3‾H symmetry. The photoluminescence emission spectra of the (Ba8.8-pCap)Eu0.2Al2Si6O24 phosphors depending on the Ca2+ ion content (p) were exploited under 365-nm excitation. When the Mn2+ emitter was co-doped in the (Ba8.8-pCap)Eu0.2Al2Si6O24 structure, the energy-transfer mechanism from Eu2+ to Mn2+ was investigated, and their electric multipole interactions were examined. The Commission Internationale de I'Eclairage (CIE) coordinates near the blue-green to orange regions of the obtained phosphors were observed. Thermal quenching with the activation energy of (Ba8.7-pCap)Eu0.2Mn0.1Al2Si6O24 (p = 2–4) phosphors in the temperature range of 298–448 K was achieved under a 365-nm light-emitting diode (LED). The tendency of the internal quantum efficiency of the (Ba5.8-qCa3)Eu0.2MnqAl2Si6O24 (q = 0.01, 0.1, 0.2) phosphors on a 365-nm LED chip was measured in addition to the color-rendering index, correlated color temperature, and CIE coordinates for the white LEDs.

Structure evolution and tunable magneto‐optical multifunctional property study of novel Ca18K3Sc1‐xSmx(PO4)14 phosphors

AbstractThe optical‐magnetic multifunctional materials are of great importance owing to their potential applications in intersect discipline fields. However, the multifunctional materials with satisfied optical and magnetic property are limited, and the modulation mechanism of their magneto‐optical property related to their structure feature is ambiguous. Here, a new multifunctional solid solution phosphors Ca18K3Sc1‐xSmx(PO4)14 (0 ≤ x ≤ 1) are designed based on composition engineering and are successfully synthesized. The detailed structure feature including the structural evolution of the crystallographic parameters and local lattice environment as well as polyhedral distortion behavior are investigated through X‐ray diffraction Rietveld structure refinement for Ca18K3Sc1‐xSmx(PO4)14 in the full range (0 ≤ x ≤ 1). The photoluminescence spectra indicate that Ca18K3Sc1‐xSmx(PO4)14 (0 ≤ x ≤ 1) can emit intense orange‐red emission (IQE~42.6%) under ultraviolet light excitation ascribed to the4G5/2 ‐6H7/2 transition of Sm3+ ions. The structure modulated luminescence behavior, for example, the tunable emission ratio of I648/I565, high quenching content, and electric multipole interaction mechanism are studied. The versatile phosphors can exhibit tunable orange‐red cathodoluminescence emission along with increasing the accelerating voltage. The electron transition mechanism of the photoluminescence and cathodoluminescence behavior is further discussed through a simple schematic diagram. Moreover, Ca18K3Sc1‐xSmx(PO4)14 (0 ≤ x ≤ 1) shows a ferromagnetic behavior with controllable magnetization and coercive field. Finally, the impact of Fe ions on the photoluminescence and magnetic property of Ca18K3Sc1‐yFey(PO4)14: 0.4Sm3+ (0 ≤ y ≤ 0.05 and y = 1) phosphors are investigated. The current research can provide some ideas and mechanism to design and investigate more novel magneto‐optical muntifunctional materials for versatile applications in intersect disciplines.

Insights into the crystal structure and multifunctional optical properties of A2CdTeO6 (A=Ba, Sr, Ca) double perovskites

Crystal structure and multifunctional optical properties of A-site substituted double perovskite compounds in A2CdTeO6 (A=Ba, Sr, Ca) system are reported in this work. These double perovskites are synthesized through high-temperature solid-state reaction route, and the crystal structure is determined using XRD, Raman and FTIR spectroscopy. The exact crystal structure is investigated by analyzing the observed number of vibrational modes in accordance with the group theoretical predictions. Even though the reported symmetry of Ba2CdTeO6 was cubic, the observed number of Raman modes corresponds to tetragonal symmetry with I4/m space group. Further vibrational analysis also points out the compounds Sr2CdTeO6, and Ca2CdTeO6 belongs to monoclinic symmetry with space group P21/n. The crystal symmetry of A2CdTeO6 (A = Ba, Sr, Ca) is further confirmed by Rietveld refinement of XRD patterns. From diffuse reflectance spectroscopy (DRS), the optical band gaps of Ba2CdTeO6, Sr2CdTeO6 and Ca2CdTeO6 were calculated as 3.3 eV, 3.8 eV and 3.9 eV respectively which correspond to wavelengths of absorption in the UV region indicating the possibility of these tellurates as suitable host lattices for novel phosphor materials. It is observed that the band gap is increased with decrease in Cd-O-Te bond angle which indicate the narrowing of conduction band with respect to octahedral tilting. Photoluminescence studies reveal that Eu3+ substituted Sr2CdTeO6 shows intense red emission under 394 nm excitation, and the dominance of electric dipole transition (5D0-7F2) over magnetic dipole transition (5D0-7F1) indicates the substitution of Eu3+ ions at the asymmetric A-site of the host. Concentration dependant PL properties show the optimum concentration of Eu3+ ions is about x = 0.14 and the critical distance for quenching effect of Eu3+ions is calculated as 9.75 Å, indicating the energy transfer mechanism involved is electric multipolar interaction. Obtained CIE color coordinates (0.643, 0.346) is close to the standard red color, and the low value of CCT (2572 K) ensure warmer red light. PL emission intensity of 0.14 Eu3+ doped Sr2CdTeO6 shows a decreasing trend with increase in temperature which indicates the potentiality of Eu3+ doped sample for temperature sensing applications. Relative sensitivity calculated for Sr2CdTeO6: 0.14 Eu3+ is 0.28 %K−1. Furthermore Judd-Ofelt intensity parameters Ωλ (λ = 2, 4) are calculated and the larger value of Ω2 compared to Ω4 confirms that Eu3+ ions occupy the asymmetric A- site of Sr2CdTeO6 host. Hence, Eu3+activated Sr2CdTeO6 can be treated as a suitable material for both photoluminescence and temperature sensing applications.

Synthesis, characterization and photoluminescence properties of Tm3+-doped Ca2YTaO6 blue-emitting phosphors

A series of Ca2YTaO6: Tm3+ blue-emitting phosphors were firstly prepared by the solid-state method. The phase formations and purity of Ca2YTaO6: xTm3+ (x = 0.3%-5% mol) were verified by X-ray powder diffraction. The morphological characteristics of Ca2YTaO6: 0.005Tm3+ were detected by scanning electron microscopy (SEM). Photoluminescence properties were discussed by emission (λem = 460 nm) and excitation (λex = 359 nm) spectra. The critical doping concentration of the products was 0.005 mol. The proposed concentration quenching mechanism in Ca2YTaO6 materials was the electric multipole interaction. Besides, the color coordinates (0.1408, 0.0891) of Ca2YTaO6: 0.005Tm3+ were located in blue region. The results suggested the Ca2YTaO6: Tm3+ phosphors can be promising blue-emitting components for the WLED applications.

Preparation and luminescence properties of Tm3+-doped SrBi2Ta2O9 blue-emitting phosphor

Various novel SrBi2Ta2O9:Tm3+ blue-emitting materials were achieved via solid-state synthesis. The structure and phase purity of prepared SrBi2Ta2O9:xTm3+ (x = 0.005-0.30 mol) were examined by X-ray powder diffraction. The surface morphology of SrBi2Ta2O9:0.01Tm3+ were studied by scanning electron microscopy. Photoluminescence properties were systematically explored under the monitoring emission (λem = 468 nm) and excitation (λex = 303 nm) spectra. The optimum mole ratio of as-synthesized phosphors was 0.01 mol. The concentration quenching mechanism in the SrBi2Ta2O9 host was due to electric multipole interaction. Particularly, the chromaticity coordinates (0.1334, 0.0474) of SrBi2Ta2O9:0.01Tm3+ are near to those of the commercial BaMgAl10O17:Eu2+. These results validated the SrBi2Ta2O9:Tm3+ phosphor can be utilized good blue-emitting candidate for W-LEDs.

Synthesis, luminescent properties and crystal stabilization of GdAG:Mn2+/Ce3+ via Y3+ doping for warm w-LED application

Abstract In this paper, the (Gd,Y)AG:Mn2+,Ce3+ phosphors were synthesized by high temperature solid-state reaction method. The lattice stabilization, microstructure and fluorescence properties were systematically investigated via XRD, FE-SEM, PLE/PL spectra and fluorescence decay analysis, respectively. Under the excitation of 461 nm, two emission peaks appear at 585 nm and 740 nm, which can be assigned to the transition 5d→4f of Ce3+ and 4T1→6A1 of Mn2+. The color of (Gd,Y)AG:Mn2+,Ce3+ phosphor can be adjusted from yellow to orange-red by changing the doping concentration of Mn2+, and the quenching mechanism of Mn2+ in (Gd,Y)AG: Mn2+,Ce3+ system is attributed to the electric multipole interactions. With the increase of Mn2+ concentrations, the fluorescence lifetime reduced from 152 ns to 9 ns, and the energy transfer efficiency of Ce3+→Mn2+ can be calculated to increase from 35.32% to 95.89%. The underlying mechanisms were thoroughly investigated and elucidated. Furthermore, the thermal stability of (Gd,Y)AG:Mn2+,Ce3+ phosphor systematically studied. The excellent fluorescence properties and high stability of (Gd,Y)AG:Mn2+,Ce3+ phosphor is expected to be widely used in lighting and display areas.