5D0 State Research Articles

High-Quantum-Efficiency Pr3+-Doped Li7La3Zr2O12 Garnet and Associated Temperature-Sensing Performance.

The understanding of energy transfer mechanisms between different excited states of Pr3+ is closely bound up with exploiting high-quantum-efficiency Pr3+-doped luminescent thermometers and optimizing their temperature-sensing performances. Herein, we propose a new-type Pr3+-doped tetragonal-phase Li7La3Zr2O12 (Pr3+:LLZO) garnet luminescent thermometer and study accompanied photoluminescence (PL) properties. Combining composition optimization, we gain a fantastic room-temperature PL quantum efficiency within Pr3+:LLZO phosphors (77.48%), a value obviously superior to those of traditional Pr3+-doped garnet-type phosphors. The thermally induced fluorescence quenching of 3P0 emissions within Pr3+:LLZO mainly originates from phonon-assisted thermal ionization, differing from the Pr3+-doped Y3Al5O12 garnet. By contrast, the 1D2 case is akin to most Pr3+-doped materials in that the quenching behavior is seriously associated with the cross-relaxation between the 3P0 and 1D2 states. On that basis, we propose a Pr3+:LLZO luminescence thermometry strategy by utilizing different quenching mechanisms of steady-state 3P0 and 1D2 emissions, performing a comparable temperature-sensing capability to those Pr3+-based garnet-type luminescent thermometers. Our findings strengthen the importance of discerning the quenching mechanisms of Pr3+ emissions and provide a valuable perspective for designing high-quantum-efficiency Pr3+-doped garnet-type luminescent materials and relevant luminescence thermometry.

Glass-ceramic materials: influence of fluoride nanocrystals on emission properties of lanthanide ions

In this work, the oxyfluoride glass-ceramic materials containing LaF3 nanocrystals, prepared by using the sol-gel method, were described. The influence of fluoride nanocrystals on the photoluminescence properties of selected lanthanide ions was determined. The experimental results obtained for nano-glass-ceramics were compared to the precursor xerogels. Those Ln3+-doped sol-gel materials with dispersed LaF3 nanocrystals exhibit several visible emission bands. It was observed that heat-treatment process caused the elongation of the lifetimes of the 5D0 state from τ = 0.22 ms to τ1 = 0.79 ms, τ2 = 9.76 ms (for Eu3+-doped materials) and of the 4F9/2 state from τ = 0.027 ms to τ1 = 0.034 ms, τ2 = 1.731 ms (for Dy3+‑doped materials). The performed studies clearly revealed that luminescence behaviour also depends on an activator concentration and a distribution of energy levels of lanthanide ions.

Leveraging photosensitive and thermally stable luminescent Ba2ZnWO6:Eu3+, M+ (M+= Na, K , and Li) nanophosphor for targeted non-invasive and stain-free visualization of cracked tooth syndrome

The cracked tooth syndrome poses a significant challenge in dentistry, thereafter untreated cases often lead to severe complications, such as pulpitis or complete tooth fracture, ultimately contributing to tooth loss. However, the conventional diagnostic methods to visualize microcracks in the tooth suffer from severe drawbacks, such as inaccurate cold stimulation, discomfort with probing, impractical staining techniques, and difficulty in distinguishing harmless craze lines from pathological cracks. To address this challenge, for the first time, we are proposing a novel approach by utilizing luminescent Ba2ZnWO6:Eu3+ (3 mol %), K+ (1 wt %) nanophosphor for improved imaging and diagnosis of cracked tooth syndrome. Herein, the double perovskite structured Ba2ZnWO6:Eu3+ (1–11 mol %), M+ (M+ = Na, K, and Li (1 wt %)) nanophosphors were synthesized via the sonochemical route. The photoluminescence emission spectra of the prepared Ba2ZnWO6:Eu3+ (1–11 mol %) nanophosphors displaying distinct peaks at 583, 595, 613, 662, and 720 nm, which ascribed to transitions from state 5D0 to 7FJ (J = 1–4) state of the Eu3+ ions, respectively. By adopting a strategic charge compensation mechanism, the enhancement in the luminescence emission intensity of about 1.5-fold was achieved after co-doping K+ (1 wt %) with Ba2ZnWO6:Eu3+ (3 mol %) nanophosphor. The photometric studies of the phosphors portray their orange-red emission with excellent quantum efficiency (82.52 %), and color purity (∼ 99 %). The emission intensity was sustained up to 73.71 % at 473 K, indicating excellent thermal stability of the phosphor. The in vitro cytotoxicity assessments of the optimized nanophosphor demonstrated its biocompatibility on normal non-malignant oral fibroblasts. The visualized microcracks in the tooth using optimized Ba2ZnWO6:Eu3+ (3 mol %), K+ (1 wt %) nanophosphor under UV excitation of UV 365 and 395 nm light revealed the orientation of microcracks, crack width, depth of the crack, and microcrack branching without any stain. The aforementioned results demonstrated that the proposed methodology paves the way for a new avenue in dental imaging technology with the potential to revolutionize and improve patient care outcomes.

Visible/near-infrared luminescence and concentration effects of Pr3+-doped Sr2Al2GeO7 downconversion phosphors

The Pr3+ ion has been widely doped into various materials as a red and near-infrared (NIR) emitting center for applications in lighting and solar spectrum downconversion. Herein, the preparation of a new library of Pr3+-doped Sr2Al2GeO7 phosphors was proved by powder x-ray diffraction patterns and Rietveld refinements and characterized by a scanning electron microscope with energy-dispersive x-ray spectrometry. The Sr2Al2GeO7:Pr3+ sample strongly absorbs blue photons over 420–500 nm and yields intense visible emissions with dominant peaks around 490 nm from the Pr3+ 3P0 → 3H4 transition, as well as robust NIR emission bands over 800–1200 nm. In addition to the typical transitions of 1D2 → 3F2 at 880 nm, 1G4 → 3H4 at 1000 nm, and 1D2 → 3F3,4 at 1070 nm, the distinguishable NIR emission at 929 nm was demonstrated from the 3P0 → 1G4 transition via static and dynamic spectroscopic analysis. Most interestingly, for the 3P0 blue-excited state, a considerably elevated concentration of about 10%Pr3+ was optimal for the visible/NIR emissions, in stark contrast to the diluted optimal 1%Pr3+ for the 1D2 state. The relevant cross-relaxation from the 3P0 and 1D2 states between Pr3+ was comprehensively treated by theoretical speculations and experimental results. Such concentrated Pr3+ blue activators would significantly facilitate the blue-to-NIR downconversion through a desired two-step sequential transition from the 3P0 initial state to the 1G4 intermediate level for quantum efficiency exceeding unity. The current results would consolidate the basis of concentrated Pr3+ donors to promote the novel Pr3+/Yb3+ codoping downconversion for greatly increasing Si solar cell efficiency.

Energy transfer of Eu3+/Dy3+ ions co-doped BaCO3 elaborated by auto-combustion process

Samples of undoped and (Eu3+, Dy3+) ions co-doped BaCO3, were synthesized by autocombustion method. The samples nanostructures were characterized by various techniques such as X-ray diffraction, scanning electron microscopy (SEM), Photoluminescence (PL) spectroscopy and electron paramagnetic resonance (EPR). Based on XRD analysis, the undoped and (Eu3+, Dy3+) co-doped BaCO3 kept its orthorhombic structure. The calculated crystallite sizes for undoped and (Eu3+, Dy3+) co-doped BaCO3 samples are 70 and 49 nm, respectively. The FTIR spectra allowed the determination of the vibration modes of BaCO3. Morphological analysis showed that the synthesized powders consist of spherical and agglomerated particles. The EPR measurements exhibited a narrow response for BaCO3, along with an increased intensity in the case of the Eu3+ doped and (Eu3+, Dy3+) co-doped samples, indicating the incorporation of Eu3+ and Dy3+ ions into the matrix. The effect of Dy3+ (0.5 %) on the luminescence properties of BaCO3:Eu3+were studied. The results indicated that the lifetimes of the state 5D0 of Eu3+ increase from 1.15 to 1.31 ms in the presence of Dy3+, proving an energy transfer from Dy3+ to Eu3+ ions. This transfer was verified also by photoluminescence spectra, quantum efficiency of the 5D0 → 7F2 emission (80 %) and the emission cross section (39×10−22 cm2). The CCT (4239 K) and CRI (87) were calculated. Therefore, Eu3+, Dy3+ co-doped BaCO3 material could be used in the fields of w-LED applications.

UVC Up-Conversion and Vis-NIR Luminescence Examined in SrO-CaO-MgO-SiO2 Glasses Doped with Pr3.

The application of ultraviolet-C light in the field of surface treatment or photodynamic therapy is highly prospective. In this regard, the stable fluorescent silicate SrO-CaO-MgO-SiO2-Pr2O3 glasses able to effectively convert visible excitation on the ultraviolet praseodymium emission were fabricated and examined. An unusual wide-range visible-to-UVC up-conversion within 240-410 nm has been achieved in Pr3+-doped glasses, revealing their potential advantage in different sophisticated disinfection technologies. The integrated emission intensity was studied as a function of light excitation power to assess a mechanism attributed to UVC luminescence. Especially, it was revealed that the multicomponent silicate glass qualities and praseodymium 3PJ excited state peculiarities are favorable to obtaining useful broadband ultraviolet up-converted luminescence. The glass dispersion qualities were determined between 450-2300 nm. The impact of praseodymium concentration on Vis-NIR spectroscopic glass qualities was evaluated employing absorption spectra, emission spectra, and decay curves of luminescence associated with two involved praseodymium excited states. Especially, efficient interionic interactions can be inferred by investigating the decrease in 1D2 state experimental lifetime in the heavily doped samples. Examination of absorption spectra as a function of temperature implied that excitation at 445 nm should be quite effective up to T = 625 K. Contrary to this, temperature elevation gives rise to a moderate lowering of the visible praseodymium luminescence.

Concentration and temperature dependence of Pr3+ f-f emissions in La(PO3)3

La(PO3)3 activated with different concentrations of Pr3+ was synthesized by a solid-state process. The obtained powder was composed of chunks of several microns in size, typical for this type of synthesis. X-ray diffraction confirmed an orthorhombic crystal structure with the C2221 space group. The electronic band structures and density of states of La(PO3)3 and La(PO3)3:Pr3+ are calculated and presented. The visible and near-infrared emissions from Pr3+ [Xe]4f2→ [Xe]4f2 electronic transitions were detected under 442 nm excitation. The red emission from the 1D2 state dominates visible spectra while emissions from the 3P0,1,2 states have smaller intensities. The 1D2 emission centered around 1020 nm is detected in the near-infrared spectral range. Intensities of 3P0 emissions increased with an increase in Pr concentration, while 1D2 emissions decreased in intensity. We found that the main process responsible for the 1D2 state decay is the Pr(1D2) + Pr(3H4) → Pr(1G4) + Pr(3F3,4) cross-relaxation between two Pr ions of electric dipole-dipole character. This finding is supported by 1D2 emission decay measurements, which revealed a reduction of average decay constants from 242 μs for a 0.5 mol% doped sample to 11 μs for a 10 mol% doped sample and an increasingly stronger non-exponential behavior of emission decay patterns with an increase in Pr3+ concentration.

Eu(tta)3(Phen-derived)] complexes: Theoretical and empirical approaches enlightening their photophysical behavior

Motivated by the high demand for efficient luminescent systems, whether new or little explored, a series of complexes based on the Eu3+ ion, coordinated with the β-diketone 4,4,4-trifluoro-1-(thiophen-2-yl)butane-1,3-dione, and several 1,10-phenanthroline derivatives (PIB, PIB_4CH3, and PIN_2OH), were synthesized, characterized, and had their optical properties evaluated using PLS. The complex containing the PIB ligand, although already reported in the literature, had its photophysical properties explored in depth and compared with those of the other complexes introduced here. The complexes containing the ligands PIB and PIB_4CH3 exhibited the highest intrinsic quantum yield values, 38.7% and 41.8%, respectively; the one containing the ligand PIN_2OH the lowest value, 16.6%, and the precursor complex [Eu(tta)3(H2O)2] an intermediate value of 28.1%. Computational calculations suggest that in the complexes containing the ligands PIB and PIB_4CH3 there is no significant back-transfer, justifying their higher values of quantum yield. However, when the PIN_2OH ligand is used, back-transfer occurs strongly between the T1 and 5D1 states, decreasing its performance in relation to the others. Therefore, the choice of the PIB ligand was appropriate to increase the emission efficiency of the complex, and among the new ligands introduced, PIB-4CH3 was the most promising for applications involving luminescent emitters.

Growth, characterization, and anti-bacterial activity of l-methionine supplemented with sulphamic acid single crystals

Abstract Sulphamic acid (SA) crystals supplemented with l-methionine (LM) were grown at moderate temperatures using a slow evaporation procedure. The powder XRD pattern showed that LM supplemented with SA (LMSA) crystals have an orthorhombic crystal structure. The FTIR studies confirmed the presence of various vibrational modes. Using a UV-Vis spectrometer, the transmittance of LMSA in the UV and visible range was observed, and the band gap of the LMSA was also calculated. The hardness value of LMSA was higher compared to that of pure SA. Photoluminescence emission studies of LMSA pointed out emissions at 491 and 542 nm, which were attributed to the transition from the 5D4 state to 7F6 and 7F5 ground, respectively. LMSA crystals were effective in killing pathogenic bacteria, according to the studies on their anti-bacterial activity.

Optical properties of Eu3+ - doped Sr2TiO4 phosphor powder synthesised by solid-phase reaction method

Fluorescent powder Sr2TiO4 doped with Eu3+ ions was synthesised by the solid-phase reaction method with a sintering temperature of 1200oC in the air with a 1-6% doping concentration. The resulting material has a perovskite structure of I4/mmm space group, and the Eu3+ ion doping concentration does not change the material’s structure. This characteristic space group of the material was also investigated through the Raman scattering spectrum with characteristic peaks at positions 145, 240, 448, and 699 cm-1 corresponding to vibrational modes with 2A1g + 2Egcharacteristic states of Sr2TiO4 material. The results showed that the material absorbs strongly in the ultraviolet and blue light regions with characteristic peaks of the Sr2TiO4 matrix and Eu3+ ions to emit strongly in the red light region with characteristic emission peaks of Eu3+ ions in the background network when moving from the excited state 5D0 to state 7Fj (j is a positive integer number). Fluorescence quenching was also observed at a doping concentration of 4% Eu3+ ions. The fabricated material is suitable for coating applications on nUV-LED LED chips.

CeF3-TbF3-YF3 nanoparticles for ratiometric temperature sensing

The Ce0.5Y0.5-XTbXF3 (X = 0.01, 0.02, 0.05, 0.1, and 0.5) nanoparticles demonstrated a single-phase hexagonal structure corresponding to CeF3 host. The average diameter was 15 ± 1 nm. Under Ce3+ excitation at 266 nm, the luminescence peaks of (5d – 4f) Ce3+ and 5D4 – 4FJ (J = 6, 5, 4, and 3) Tb3+ were observed. The emission peaks from 5D3 level of Tb3+ were not observed. We took the luminescence integrated intensity ratio (LIR) of Ce3+ and Tb3+ peaks as a temperature-dependent parameter (303–523 K range). The LIR functions decay with the temperature increase. Indeed, with the temperature rise, the depopulation rate of Ce3+ excited state by Tb3+ becomes higher (phonon-assisted process). Thus, the ICe/ITb decreases. However, the rate of the LIR decay decreases with the increase of Tb3+ concentration. It was suggested, that this phenomenon is related to the presence of two competing processes populating the 5D4 state of Tb3+. There are phonon-assisted non-radiate transition from 5D3 to 5D4 of Tb3+ and cross-relaxation between Tb3+ ions, which was considered less temperature-dependent. The contribution of less temperature-dependent cross-relaxation process to the population of 5D4 increases with the Tb3+ concentration increase compared to 5D3 – 5D4 non-radiative transition. More significant contribution of the cross-relaxation leads to the decrease in the LIR descent rate. The maximum Sa and Sr values were 0.19 K-1 and 1.74 %/K at 303 K, respectively.

UV/ visible/ NIR sensitized enhanced green luminescence of a newly synthesized salicylic acid coated Tb3+ and Yb3+ ions doped Y2O3 nano-composite phosphor: Prospect as luminescence solar collector material

The present work describes the enhancement of green luminescence of Tb3+ ion in a newly synthesized composite material that contains Tb3+ and Yb3+ ions in Y2O3 nano-phosphor (TYY) coated with salicylic acid (SA) doped polyvinyl alcohol (PVA) polymer matrix (TYY: SA/PVA). XRD results reflect nearly 50 nm size of crystallite in TYY phosphor. On coating, the same with SA-doped PVA polymer visualizes the actual particulate size in microns due to aggregation of nano-crystallites of TYY and indicates the formation of organic/inorganic composite material. In down-conversion of UV radiation, both singlet and triplet states of excited state intra-molecular proton transfer species of SA in TYY: SA/PVA composite material transfer their UV (200 nm–370 nm) excitation energy through Fӧrster and Dexter mechanism to 5D4 state of Tb3+ ions, which enhances green luminescence of Tb3+ ions [5D4 →7F5] by nineteen-fold and decrease in the NIR luminescence intensity of Yb3+ ion [2F5/2 → 2F7/2] in TYY/SA/PVA as compared to the TYY sample indicates coating of SA/PVA polymer on the nano phosphor blocks the quantum cutting process from 4f75 d1 excited state of Tb3+ ions to 2F5/2 state of Yb3+ ions. In contrast, TYY: SA/PVA and TYY material exhibit intense green luminescent emission of Tb3+ ions by up-conversion of NIR radiation through a cooperative energy transfer between two Yb3+ ions [2F5/2 → 5D4 excitation]. A thin layer coating of composite phosphor material shows enhancement in the external quantum efficiency of the solar cell by increasing the efficiency of ∼3–5 % in the 400 nm–1000 nm range compared to the bare solar cell. I–V characteristics of the composite show that simultaneous excitation of this composite material with UV/Visible/NIR radiation increases the photon density in blue, green, and NIR regions for reabsorption by the photovoltaic cell. This preliminary study signifies the scope for developing brighter, high photon flux luminescent composite luminescent solar collecter material with low cost.

Improvement of Luminescence Performance by the Addition of KF in the Eu2O3 Doped Li2O-AlF3-NaF-P2O5 Glass for Highly Efficient Reddish-Orange Laser Application

One mol% of europium (Eu3+) with the addition of potassium fluoride in Li2O-AlF3-NaF-P2O5 glass has been prepared using a melt-quenching technique. The fluorescence properties of present glasses were studied by the physical properties, FTIR (Fourier transform infrared spectroscopy), absorption spectra, photoluminescence properties, radiative properties and photometric analysis. The physical properties were measured to know the compactness of the glasses. The structural behavior of groups PO4 and OH of the glasses was discussed through the FTIR spectra. From the FTIR spectra, the OH group of adding KF into the glass showed a low %T intensity due to the hydroxyl group that was consumed by the fluoride content, which confirms the low phonon energy. Using absorption spectra and Judd–Ofelt’s (J–O) theory, the J–O intensity parameters (Ω2, Ω4, and Ω6) and radiative emission properties of excited states of Eu3+ ions are calculated to confirm potential laser applications. Photoluminescence properties generated excitation, emission, and lifetime for the glasses. It is observed that the enhancement of the Eu3+ emission at 613 nm is because of the addition of potassium fluoride. It proved the lifetime associated with the transition from the 5D0 state to be a single exponential. The CIE (Commission International de I’Eclairage) chromaticity diagram estimated the CIE color coordinates and color purity of the prepared glasses. The UV lamp under wavelength at 365 nm achieved reddish-orange emissions, which is suitable for reddish-orange laser applications.

Structural and luminescent performance and optical thermometry of Pr3+ doped SrWO4 down-conversion phosphors

A series of Pr3+ doped SrWO4 phosphors were synthesized using solid-state reaction routes. The phase composition, photoluminescence and temperature sensitivities of as-prepared materials were investigated. Rietveld refinement of measured XRD data was applied to analyze the lattice parameters. The optical transition was elaborated using UV–visible diffuse reflectance spectra and photoluminescence spectra. The photoluminescence measurements confirmed the strong visible light emission from the developed phosphors under both UV excitation at 250 nm and blue excitation at 450 nm. Notably, the maximum emission intensity was observed at a Pr3+ doping concentration of 2 mol%. Furthermore, the fluorescence intensity ratio (FIR) technique was employed, focusing on the emissions originating from the 3P0 and 1D2 state of Pr3+ within the temperature range of 298–598 K. Two FIR groups were adopted in this case, which can verify each other to achieve self-calibration. Typically, SrWO4:0.02Pr3+ exhibited remarkable performance as a temperature sensor, displaying an absolute sensitivity (Sa) of 3.11%K−1 and a relative sensitivity (Sr) of 0.81%K−1. As a result, the significant temperature-dependent PL and remarkable down-conversion luminescence make the SrWO4:Pr3+ material a promising candidate for optical thermometers and UV to visible converters of solar cell applications.

Structural and luminescence properties of transparent borate glass co-doped with Gd3+/Pr3+ for photonics application

A new glass system of lithium borate doped with Gd2O3 and Pr2O3 has been fabricated using a conventional melt quenching technique. The physical parameters, such as density, molar volume, and refractive index, were measured and found to increase as the concentrations of lanthanide oxide (Gd2O3 and Pr2O3) in the glass increased, revealing the underlying structural changes. According to the results of XRD and FTIR, the synthesized glasses exhibited an amorphous structure, and borate complexes served as the triangular BO3, tetrahedral BO4, and OH group amounts in oxide glass. The photoluminescence (PL) spectra show characteristic emission bands resulting from f-f transitions of Pr3+ ions. The strongest emission occurred at 603 nm, corresponding to the transition from the 1D2 state to the 3H4 state. The optimal concentration of Gd2O3 for maximizing emission intensity was found to be 5.0 mol%, and this concentration will be used in the next experiment with varying Pr2O3 concentrations. In the subsequent experiment, emission spectra were recorded by exciting the glass with light at wavelengths of 445 nm, 469 nm, and 483 nm. The resulting emission spectra displayed the characteristic pattern associated with the emission of Pr3+. This emission peak at 603 nm represented the strongest intensity in the spectra, which is a common characteristic of Pr3+ emission. The emission intensity of the glasses initially increases with increasing concentrations of Pr2O3 up to 0.3 mol%, but beyond this concentration, the emission intensity starts to decrease. This behavior indicates the occurrence of a quenching effect at the 0.3 mol% concentration of Pr2O3. X-ray absorption near-edge structure (XANES) analysis confirmed that praseodymium ions were predominantly in the 3 + oxidation state. The chemical composition of the created glass was confirmed to be suitable for photonics applications.

Effective role of Co-dopants (Dy3+, Sm3+) on Tunable multicolour emission of Tb3+ doped telluroborate glasses for Natural White light applications

In the current work the efficacy of incorporation of Dy3+ and Sm3+ ions into Tb3+ doped new telluroborate glass as well as their interactions was investigated. In this study, Tb3+ ions were employed as activators and sensitizers for both Dy3+ and Sm3+ ions emissions, which emanate from the excited states of Dy3+ (4F9/2) and Sm3+ (4G5/2) ions through a non-radiative energy transfer process. To validate the emission gamut of the prepared glasses, distinct emission colours were inspected with the CIE 1931 chromaticity analysis and the appropriate correlated colour temperature (CCT) values were estimated. The emission decay profile relating to the Tb3+ ions (5D4 state) of the glasses was investigated. The energy transfer efficiency, which stems from Tb3+ ion to Dy3+ and Sm3+ ions were found to be 49 and 54% respectively. The IH model was successfully used to analyse the interaction mechanism.

The Influence of Halide Ion Substitution on Energy Structure and Luminescence Efficiency in CeBr2I and CeBrI2 Crystals.

This study aims to determine the optimum composition of the CeBr1-xIx compound to achieve the maximum light output. It is based on calculations of the band energy structure of crystals, specifically taking into account the characteristics of the mutual location of local and band 5d states of the Ce3+ ions. The band energy structures for CeBr2I and CeBrI2 crystals were calculated using the projector augmented wave method. The valence band was found to be formed by the hybridized states of 4p Br and 5p I. The 4f states of Ce3+ are located in the energy forbidden band gap. The conduction band is formed by the localized 5d1 states, which are created by the interaction between the 5d states of Ce3+ and the 4f0 hole of the cerium ion. The higher-lying delocalized 5d2 states of Ce3+ correspond to the energy levels of the 5d states of Ce3+ in the field of the halide Cl0 (Br0) hole. The relative location of 5d1 and 5d2 bands determines the intensity of 5d-4f luminescence. The bottom of the conduction band is formed by localized 5d1 states in the CeBr2I crystal. The local character of the bottom of the conduction band in the CeBr2I crystal favors the formation of self-trapped Frenkel excitons. Transitions between the 5d1 and 4f states are responsible for 5d-4f exciton luminescence. In the CeBrI2 crystal, the conduction band is formed by mixing the localized 5d1 and delocalized 5d2 states, which leads to quenching the 5d-4f luminescence and a decrease in the light output despite the decrease in the forbidden band gap. CsBr2I is the optimum composition of the system to achieve the maximum light output.

UV excitable GdSr2AlO5:Eu3+ red emitting nanophosphors: Structure refinement, photoluminescence, Judd-Ofelt analysis and thermal stability for w-LEDs

Combustion derived Gd1−xSr2AlO5:x mol% Eu3+(x = 1–5 mol%) nanophosphors have tetragonal structure with space-symmetry of I4/mcm (space group no. 140), which was supported by X-ray diffraction patterns. Rietveld refinement pattern revealed that the doping of Eu3+ ions expanded the lattice constants/volume and shifted the diffraction peaks to a lower angle side. Investigations using SEM and TEM confirm the excellent morphology with almost spherical particles in nanoscale. The production of material with the proper stoichiometry was confirmed by EDX analysis. Optical band-gap value (5.21 eV) of optimum Gd0.97Sr2AlO5:3 mol% Eu3+ which was determined by Kubelka-Munk model, showed the good optical quality of the samples. At 268 nm excitation wavelengths, PL spectra characteristics show a strong red emission at 612 nm that corresponds to the doped Eu3+ ions hypersensitive 5D0→7F2 transition with good asymmetric ratio. The optimal doping concentration of Eu3+ ions in GdSr2AlO5 is determined to be about 3 mol% and the concentration quenching phenomenon arise from the electric dipole-quadrupole interaction. Additionally, the Judd-Ofelt investigation of GdSr2AlO5:Eu3+ phosphors were intended to determine the coordinated Eu3+ environment inside the host matrix. The experimental life time analysis of the excited state 5D0 was determined to be in the millisecond range and the quantum efficiency for optimum sample was found to be 67.62 % yielding a good white light emission. The temperature dependent luminescence behavior of Gd0.97Sr2AlO5:3 mol% Eu3+ phosphor exhibits its good thermal stability and the activation energy for thermal quenching characteristics is calculated to be 0.216 eV. The potential applicability of GdSr2AlO5:Eu3+ nanophosphor in the production of wLEDs was further improved by the color coordinates.

Correlating O-deficiency and luminescence property of Tb3+ doped SrO

Cubic rock salt can lower down or break the rare earth transition barrier through interstitial or vacancy defects owing to its great deformation and rotation flexibility. Here, we demonstrate that oxygen vacancies in SrO are induced by proper oxidization and atmosphere adjustment, resulting in defects with various depths and crystal field distortion. The thermally assisted tunneling from defects to 5D4 state and electronic population decrease on 5D3 state of Tb3+ are observed by the deformation of adjacent oxygen octahedral structure. Finally, the as-prepared SrO: 0.01 Tb3+ phosphors, commercial BaMgAl10O17: Eu2+ blue phosphor, and CaAlSiN3: Eu2+ red phosphor are mixed and coated onto 280 nm deep-ultraviolet LED chip to assemble white light-emitting LED device. The LEDs show CCT of 3850 K, 4136 K, and 4741 K, with color rendering index of 90.3, 90.8, and 92.1, respectively. These insights will advance the fundamental knowledge of crystal engineering in cubic rock salt, and enable new ways to manipulate energy transfer and electronic transition via defects.

Commercial 3D resin blended with TTA functionalized CaWO4:Eu (III), synthesis route and a luminescence study

Synthesis and characterization of calcium tungstate-based micro-nanophosphors are reported in the present work. These materials were synthesized by spray pyrolysis technique. According to Scanning Electron Microscopy measurements, CaWO4 and CaWO4:Eu (III) have quasi-spherical shape. CaWO4 presents blue luminescence whose origin is an electron transition within unperturbed WO42− complexes, while CaWO4:Eu (III) luminescent properties are generated by the presence of Eu (III) ions, which produced light emissions at 591, 615, 655, and 702 nm. Such emissions are due to radiative transitions from the excited state 5D0 to 7Fj (j = 1, 4) inter-level transitions within Eu (III) electronic energy states. These phosphors were blended with a commercial 3D print photocurable resin (Sain Smart 101-90-840TS) and their luminescent properties were transferred to resin. Besides in this case, blended 3D resin has an intrinsic blue luminescence due to its π and π* bonds which is activated under 380 nm excitation wavelength, however blended 3D resin can be also activated under 465 nm excitation which only activates Eu (III) ions producing a red emission 3D luminescent photocurable resin.