Intense Red Emission Research Articles

Exploring the influence of emissive centers in mono and dinuclear europium(III) complexes for advance lighting applications: Synthesis, characterization and computational modelling

The combination of 4,4,4-trifluoro-1-phenyl-1,3-butanedione (TFPB) and pyrazine (pyz) with Eu3+ ions results in the formation of two distinct types of complexes, characterized by general formulae [Eu(TFPB)3(L)2] (here, L is either H2O or pyrazine) and [(Eu(TFPB)3)2pyz]. The impact of surrounding environment on the photophysical properties of synthesized complexes was thoroughly examined. Photoluminescence (PL) analysis revealed the dominance of electric dipole (ED) transition (5D0→7F2) in these complexes. Theoretical calculations via Judd-Ofelt analysis were also performed. These complexes exhibit visible luminescence in both solid and solvated forms. Notably, the luminescence intensity of prepared dinuclear complex is found to be manifolds greater than its mononuclear analogues, affirming the contribution of both metal centers towards emission intensity. Furthermore, the absence of ligand centered emission in prepared complexes suggests the effective energy transfer from coordinated moieties to metal center. CIE color coordinates of prepared Eu(III) complexes, in both solid and solution media, exhibited intense red emission. DFT calculations were conducted to elucidate the distribution of electronic density in synthesized complexes. Additionally, a comprehensive analysis of these complexes, including IR, UV, NMR, thermogravimetry and cyclic voltammetry was conducted.

Pressure-assisted sintering approaches for up-converting LiYF4:Er/Yb transparent oxyfluoride glass-ceramics

Glasses of compositions 40SiO2-25Al2O3-18Li2O-7LiF-(10-x-y)YF3-xErF3-yYbF3 (mol.%, x = 0.1, 0.5; y = 0, 0.4, 2, 4) were prepared by melt-quenching technique and milled into powders. Glass powder pellets were treated by hot pressing at defined temperatures to obtain the corresponding glass-ceramics (GCs). High-resolution TEM and XRD analysis revealed the crystallization of LiYF4 and LiAlSiO4 phases with nano-crystal size below 50 nm, resulting in translucent GCs. The density of GCs was 98–99.5 % compared to parent glasses. GCs exhibited intense up-conversion emission when excited by near-infrared light at 980 nm. As Er3+ concentration increased from 0.1 to 0.5 mol.% in the samples, notable enhancement in green and red emission intensities was indicated. Yb3+ ions significantly facilitated up-conversion emission through energy transfer to Er3+ ions, resulting in a higher luminescence yield compared to Er3+ single-doped GCs. The tuning of the red to green emission intensity ratio can be achieved by varying Er3+ and Yb3+ concentrations and Er3+/Yb3+ ratio.

Theoretical and experimental investigation of BaY2(MoO4)4:xSm3+ phosphors

In this paper, the novel BaY2(MoO4)4:xSm3+ phosphors with strong red emission and high thermal stabilization were prepared by a conventional method of high temperature solid state reaction in air atmosphere. Morphology, phase purity, element distribution, UV–Vis–NIR diffuse reflectance spectroscopy (DRS), and luminescence properties were investigated in detail. The crystal structure of the BaY2(MoO4)4 host was refined with the aid of the Rietveld refinement method by the GSAS program. The electronic band structure and phonon dispersion were performed using plane-wave density functional theory (DFT). The prepared BaY2(MoO4)4:Sm3+ phosphor exhibits excellent red emission under near-ultraviolet excitation. Strong red emission intensity and high thermal stability suggest potential application in backlighting or phosphor-covered white light-emitting diodes (pc-LEDs).

STRUCTURAL AND LUMIENESCENT STUDY OF EUROPIUM (III) DOPED TUNGSTATES

Motivated by the need of new red phosphor for white - light - emitting diodes (WLEDs) application, Eu3+ doped Sc2-xInx(WO4)3 (x = 0, 1, 2) solid solutions were synthesized by high temperature solid - state reaction. Structural and luminescent properties were obtained by using X - ray diffraction (XRD), infrared and photoluminescence spectroscopic techniques. IR spectrum of the ScIn(WO4)3 doped with Eu3+ contains the characteristic vibrations of the WO4 and MeO6 , (Me = Sc, In) polyhedral, building the Sc2(WO4)3 and In2(WO4)3 structures. An effective energy transfer from the tungstate matrix to the active Eu3+ ion was observed. Intense red luminescence was obtained in these samples under excitation at 394 nm using the sharp 7F0 → 5L6 transition of Eu3+. The calculated asymmetric ratio ( 5D0 → 7F2 / 5D0 → 7F1 ) was about 7.5, suggesting that the obtained materials are characterized with distorted environment around the rare earth ion and with high red emission intensity. The prepared ScIn(WO4)3 solid solution demonstrates the highest emission intensity. The obtained chromaticity coordinates of the Eu3+ doped Sc2-xInx(WO4)3 solid solutions were very close to the red standard recommended by National Television Standards Committee (NTSC).

Fabrication and luminescent properties of highly transparent novel high-entropy (Lu0.2Y0.2Gd0.2Yb0.2Er0.2)2O3 ceramic

The highly transparent novel high-entropy (Lu0.2Y0.2Gd0.2Yb0.2Er0.2)2O3 ceramic was successfully fabricated by the addition of 3 at.% ZrO2 and 10 at.% La2O3 introduced as sintering additives via vacuum sintering. A single-phase solid solution cubic structure of the ceramic was obtained with a relative density of 99.95 % and an average grain size of 6.91±3.28 µm. The grain boundary of the (Lu0.2Y0.2Gd0.2Yb0.2Er0.2)2O3 ceramic was clean with a thickness of only 1.3 nm. Further observations revealed uniform distribution of all elements in the grains, and the presence of La and Zr segregation (1.5 nm thick) at few grain boundaries, but causing very little light scattering. The in-line transmittance of high-entropy (Lu0.2Y0.2Gd0.2Yb0.2Er0.2)2O3 ceramic reached 80 % at 1100 nm, which was 98.7 % of the theoretical value of Er2O3 single crystal. Also, there were fluorescence emissions observed in the ultraviolet (311 nm), visible (563, 622 nm), and near-infrared (1032, 1535 nm) regions. In addition, the intense red emission and weak green emission were detected, and the broad emission with a peak at 1.5 μm was attributed to Stark splitting of Er3+ ions, so the corresponding mechanism was discussed. Results obtained suggest that the highly transparent novel high-entropy (Lu0.2Y0.2Gd0.2Yb0.2Er0.2)2O3 ceramic fabricated in this study could have broad application prospects in optical applications such as scintillators, up-conversion luminescent materials, and infrared lasers.

Inducing Multicolour emission in MEH-PPV/TiO2 nanocomposites

Fluorescence-based polymers have a wide variety of applications such as light-emitting diodes, optoelectronics, and biosensors. The present study endeavors towards the effect of TiO2 nanoparticles (calcined at various temperature) on the emission of Poly [2-methoxy-5-(2-ethylhexyloxy)-1, 4-phenylenevinylene] (MEH-PPV) and to induce multicolor emission. The TiO2 nanoparticles synthesized by sol-gel method were calcined at 400°C and 600°C. In situ polymerization was adopted to synthesize MEH-PPV / TiO2 nanocomposites and the structural characteristics of the nanocomposites were studied using Fourier transformed Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). The photo-physical characteristics of the nanocomposites were investigated using UV-Visible spectroscopy, Photoluminescence spectroscopy, and Fluorescence microscopy. TiO2 nanoparticles calcined at 400°C demonstrates anatase phase, whereas the particles calcined at 700°C exhibits mixed phase of rutile and anatase. The study reveal that calcination temperature has a strong impact on the morphology of the synthesized nanoparticles. The photoluminescence spectra reveal that the incorporation of TiO2 nanoparticles enhances the red orange emission intensity of MEH-PPV, additionally exhibits emission at multiple wavelengths. Fluorescence microscopy evidences multiple colour emission from MEH-PPV/TiO2 nanocomposites. The multiple emission in the polymer nanocomposite is arised from the oxygen vacancies present in anatase and rutile phases of TiO2 nanoparticle.

Synthesis and Properties of a Red Na5Zn2Gd1−x(MoO4)6: xEu3+ Phosphor

Novel Eu3+-doped Na5Zn2Gd(MoO4)6 triple molybdate phosphors were fabricated by the sol-gel method. The structure, morphology, and luminescent properties have been characterized by X-ray diffraction (XRD), thermogravimetric differential thermal analysis (TG-DTA), scanning electron microscopy (SEM), FTIR spectroscopy, and luminescence spectroscopy. The results indicated that the synthesized Na5Zn2Gd1−x(MoO4)6: xEu3+ phosphor consisted of a pure phase with monoclinic structure. Under excitation at 465 nm, the Na5Zn2Gd1−x(MoO4)6: xEu3+ phosphor exhibits an intensive red emission band around 610 nm corresponding to the transition of 5D0→7F2 which is much higher than that 5D0→7F1 at 594 nm, which was appropriate for a blue LED. According to the influence of the synthesis conditions, the phosphors showed the highest emission intensity when the doping concentration of Eu3+ was 25 mol.% and the molar ratio of citric acid to metal ions was 2:1. Na5Zn2Gd0.75(MoO4)6: 0.25 Eu3+ with the color coordinates (x = 0.658, y = 0.341) is a more stable red phosphor for blue-based white LEDs than the commercial Y2O2S: Eu3+ red phosphor (0.48, 0.50) due to its being closer to the NTSC standard values (0.670, 0.330).

Effect of Urea and Thiourea on the color emission of (YxBi1-x)2Zr2O7:Er3+,Yb3+ upconversion phosphors

This study reports the upconversion emission properties of Bi2Zr2O7:Er,Yb (BiZr), Y2Zr2O7:Er,Yb (YZr) and (Y0.25Bi0.75)2Zr2O7:Er,Yb (Y0.25Bi0.75Zr) phosphors. All those samples were synthesized with fixed Er and Yb concentrations of 2 and 20 mol%, respectively. The analysis by X-ray diffraction revealed that the YZr sample had cubic phase, the BiZr sample had a mixture of monoclinic/cubic phases and the Y0.25Bi0.75Zr sample had a mixture of all the phases mentioned above. In addition, the analysis by electron microscopy indicated that all the samples are formed by mixtures of particles with irregular and quasi-spherical shapes. The YZr, BiZr and Y0.25Bi0.75Zr samples were synthesized using urea or thiourea as fuel and an annealing temperature of 775 or 850 °C. For any fuel, the samples produced green (525 and 548 nm) and red (655 nm) emissions by upconversion after exciting them with 975 nm. Interestingly, the Y0.25Bi0.75Zr sample always presented the most intense emission for any fuel or temperature of synthesis. Interestingly, the Y0.25Bi0.75Zr sample made with thiourea had a green emission intensity 49 % higher than that made with urea, but the red emission intensity was 25 % lower in the sample made with thiourea. Color emission tuning was observed in the samples under certain conditions: 1) the color emission for the BiZr sample (made with urea) was changed from yellow to orange-red after increasing the annealing temperature from 775 or 850 °C and 2) the YZr sample (annealed at 775 °C) changed its color emission from green to red after using thiourea instead of urea. Surprisingly, the Y0.25Bi0.75Zr sample always maintained its green emission despite the change of fuel or annealing temperature. In general, the results of this research demonstrate that different fuels or synthesis temperatures can be used to enhance the upconversion emission or to tune the emission color. This avoids the use of high concentrations of rare earths to produce any of these effects as previously reported in the literature.

Self-reducing induced Eu2+/Eu3+ dual-emitting glasses for anti-counterfeiting and optical thermometry

Eu3+/Eu2+ co-doped glasses possess extensive application potential in diverse fields, including light-emitting diodes and sensors, due to their distinctive luminescent characteristics. To date, numerous strategies have been devised to facilitate the coexistence of Eu3+ and Eu2+ in materials. Among them, adjusting the composition of the glass matrix stands out as a straightforward and reproducible approach. Herein, a series of Eu2+/Eu3+ co-doped borosilicate aluminate glasses were successfully synthesized via a high-temperature melting method. By elevating the ratios of B2O3/MgO and Al2O3/BaO in the matrix, a remarkable self-reduction of Eu3+ in ambient air was achieved because of the structural weakness and lower optical basicity for the designed glass matrix. The reduction of Eu3+ is also related to the formation of EuZn• and VΖn′′ defects. Furthermore, by fine-tuning the melting duration and Eu content, we achieved comparable violet and red emission intensities for both Eu2+ and Eu3+ ions. Under UV irradiation with various wavelengths, anti-counterfeiting patterns fabricated from glass powder exhibited precise and pronounced color changes. Notably, the emission intensity ratio of Eu2+/Eu3+ exhibited a consistent decrease as temperature increased, enabling precise temperature determination with exceptional absolute sensitivity (1.22 % K−1) producibility, and discrimination. These findings hold significant implications for the design of Eu3+/Eu2+ co-doped inorganic multifunctional glasses.

Tuneable Red and Blue Emission of Bi3+-Co-Doped SrF2:Eu3+ Nanophosphors for LEDs in Agricultural Applications.

Tunable blue/red dual-emitting Eu3+-doped, Bi3+-sensitized SrF2 phosphors were synthesized utilizing a solvothermal-microwave method. All phosphors have cubic structure (Fm-3m (225) space group) and well-distinct sphere-like particles with a size of ~20 nm, as examined by X-ray diffraction and transmission electron microscopy. The diffuse reflectance spectra reveal a redshift of the absorption band in the UV region as the Bi3+ concentration in SrF2: Eu3+ phosphor increases. Under the 265 nm excitation, photoluminescence spectra show emission at around 400 nm from the host matrix and characteristic orange 5D0 → 7F1,2 and deep red 5D0 → 7F4 Eu3+ emissions. The red emission intensity increases with an increase in Bi3+ concentration up to 20 mol%, after which it decreases. The integrated intensity of Eu3+ red emission in the representative 20 mol% Bi3+ co-doped SrF2:10 mol% Eu3+ shows twice as bright emission compared to the Bi3+-free sample. To demonstrate the potential application in LEDs for artificial light-based plant factories, the powder with the highest emission intensity, SrF2: 10Eu, 20 Bi, was mixed with a ceramic binder and placed on top of a 275 nm UVC LED chip, showing pinkish violet light corresponding to blue (409 nm) and red (592, 614, and 700 nm) phosphors' emission.

Photoluminescence investigations on Sm3+/Eu3+ co-doped Sr3NaSbO6 nanorod-shaped red phosphor for W-LEDs and indoor plant growth LEDs

Red phosphors have garnered an important role in white light-emitting diodes (W-LEDs). Herein we report the structural and luminescent properties of red-emitting Sr(3-x-y)NaSbO6: xSm3+/yEu3+ (SNSO: xSm; yEu) phosphors. Under 350 nm excitation, phosphors emit intense red emission peaking around 689 nm owing to the SNSO host emission. Optimized singly doped SNSO: 0.1Sm and SNSO: 0.2Eu phosphors have intense orange-red and red emissions under 405 and 305 nm excitations respectively. For the codoped SNSO: 0.1Sm; yEu phosphors (y = 0.1, 0.15, 0.2, 0.25, and 0.3 mol), the emission peaks of the host, Sm3+, and Eu3+ ions were present. The energy transfer from the host to Sm3+/ Eu3+ ions and from Sm3+ to Eu3+ ions was identified to be via dipole-quadrupole and quadrupole–quadrupole interactions respectively. Effective red tuning along with high color purity and warm CCT values suggest the suitability of prepared nanorod phosphors for W-LEDs and indoor plant growth LEDs.

Designing Tb3+‐Sensitized Silica‐Nanoparticles‐Aided Eu3+‐Doped Sr2SiO4 Phosphors with Enhanced Luminescence for Anti‐Counterfeiting Applications

Silica‐nanoparticles‐assisted Eu3+‐doped Sr2SiO4 and Tb3+‐ and Eu3+‐co‐doped Sr2SiO4 phosphors, as potential phosphors for anti‐counterfeiting application are synthesized via a solid‐state reaction technique. The crystal structure, photoluminescence, and decay times are investigated. The characteristic emission of Eu3+‐doped Sr2SiO4 phosphors exhibits two major peaks at 617 and 595 nm under an excitation wavelength of 394 nm, which corresponds to 5D0 → 7F2 and 5D0 → 7F1 electron transitions of Eu3+ ions. Upon co‐doping with Tb3+, the red emission intensities of the Eu3+‐doped Sr2SiO4 phosphors are enhanced by 1.78‐fold times through an energy‐transfer process. The optimized Tb3+‐ and Eu3+‐co‐doped Sr2SiO4 phosphors show a decay time of 0.49 ns and an energy‐transfer efficiency of 73%. The calculated International Commission on Illumination value (x, y) and color purity are (0.63, 0.37) and 94%, respectively. Subsequently, a luminescent ink is formulated using the optimized phosphor and tested for efficiency on currency notes. Additionally, a flexible film is fabricated, and its luminescence properties are studied. The formulated ink can serve as security ink in the anti‐counterfeiting application.

Enhanced red UC emission of Er3+ ions by constructing multi-heterojunction core-shell nanoparticles

The construction of core-shell structures with multiple heterojunctions facilitates ion energy transfer and minimizes surface quenching effects, which are essential for enhancing and regulating the upconversion emission of materials. In this study, we effectively regulated the spatial distribution of Yb3+ and Er3+ ions in multilayered heterogeneous core-shell structures to significantly enhance the red upconversion emission of Er3+ ions. Specifically, the red emission intensity of the NaErF4@NaYbF4: 2 %Er3+@NaYF4 core-shell nanoparticles was enhanced nearly 24.4-fold compared to that of NaErF4 nanoparticles. This enhancement results from a bidirectional energy transfer process. Moreover, when we swapped the positions of the NaErF4 core and the NaYbF4: 2 %Er3+ shell and introduced NaYF4 inert isolation layer and Yb3+ ions, the red emission intensity of the NaYbF4:2 %Er3+@NaYF4:20 %Yb3+@NaErF4@ NaYF4 multilayer core-shell structure increased significantly by nearly 254.3-fold compared to NaErF4 nanoparticles. The remarkable enhancement of the red emission of Er3+ ions is primarily attributed to a well-organized bidirectional energy transfer process between the heavily doped core and shell Er3+-Yb3+ ion pairs. The energy transfer behavior of these multi-heterojunction core-shell nanoparticles was studied based on their spectral characteristics. The multilayer heterogeneous core-shell nanoparticles exhibited colorful emissions under different excitation conditions, highlighting their potential for biomedical applications and colorful anti-counterfeiting.

Ligand-to-Metal Energy Transfer in terbium and europium oxalate heptahydrate crystals: Understanding the influence of oxalate ligand on the photoluminescent properties

The intense green and red emission of terbium and europium oxalates are attributed to the cross-relaxation process between lanthanide ions. However, the role of the organic ligand as a sensitizing agent for the emission has not been fully elucidated, leaving the photoluminescent (PL) properties relatively unexplored. This work presents a comprehensive study of the Ligand-to-Metal Energy Transfer (LMET) in terbium and europium oxalates heptahydrate. Single crystals were grown using the hydro-silica gel technique, and a novel improvement of the synthesis procedure which allowed growing substantially larger europium oxalate crystals than in previous studies in the field is also reported. X-ray diffraction (XRD), Fourier-Transform Infrared spectroscopy (FTIR), and thermogravimetric analysis confirmed the chemical composition RE2(C2O4)3⋅7H2O. PL studies provided reliable evidence of a sensitized emission via the antenna effect, indicating that the LMET contributes to the population of the 5Dj emissive levels of Ln3+ ions, assisting the cross-relaxation process. These findings enhance our understanding of the PL properties of terbium and europium oxalates and demonstrate that the oxalate ligand is a more effective luminescent sensitizer for Tb3+ ions than for Eu3+ ions. Additionally, PL excitation studies on terbium and europium oxalate decahydrate crystals were conducted to contrast the emission properties between both forms of hydrate oxalates. Notably, terbium oxalate heptahydrate crystals exhibit a significant improvement in the Charge Transfer (CT) due to higher intramolecular charge transfer.

A novel high-brightness red phosphor Ca4Nb2O9: Eu3+ for WLEDs

In this study, new phosphors Ca4Nb2O9 doped with Europium (Eu3+) ions were created using a high-temperature solid-state method. Characterizations with X-ray diffraction (XRD), Rietveld refinement, scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDS) and elemental mapping revealed successful doping and uniform elemental distribution. The band gap is 4.17 eV for Ca4Nb2O9 and 3.73 eV for Ca3.7Nb2O9: 0.3Eu3+, which is shown that the band gap decreases with increasing concentration. Subsequently, the samples underwent photoluminescence (PL) spectra testing, revealing that the Ca4Nb2O9: Eu3+ phosphors exhibited intense red emission when excited at 395 and 465 nm. Meanwhile, the principal emission peak resided at 613 nm, and the ideal doping concentration of Eu3+ was determined to be x = 0.3. In addition, at 420 K, the luminous intensity of Ca3.7Nb2O9: 0.3Eu3+ under 395 and 465 nm excitation is 60 % as well as 82 % of its strength at 300 K, respectively, indicating excellent thermal stability. Furthermore, the phosphor exhibits a relatively high quantum efficiency, reaching 45.47 % when excited with 395 nm light and 58.17 % when excited with 465 nm light. Finally, a white light-emitting diode (WLED) device with a Ra value of 86.3 and correlated color temperature (CCT) of 4450 K was fabricated. The results suggest that the prepared phosphor, in combination with a near-ultraviolet (NUV) light-emitting diode (LED) chip, has the potential for application in white light-emitting diodes.

Hierarchical Self-Assembly and Aggregation-Induced Emission Enhancement in Tetrabenzofluorene-Based Red Emitting Molecules.

The newly synthesized chiral active [5]helicene-like tetrabenzofluorene (TBF) based highly red-emitting molecules exhibit flower-like self-assembly. These molecules display photophysical and structural properties such as intramolecular charge transfer, dual state emission, large fluorescence quantum yield, and solvatochromism. In TBFID, the indandione functional group attached on both sides as the terminal group offers an A-D-A push-pull effect and acts as a strong acceptor to cause more redshift in solution as well as in solid state as compared to TBFPA (TBF with benzaldehyde functional group in terminal position). The self-assembly studies of TBFID demonstrate the aggregation-induced emission enhancement (AIEE) attributed to the restriction of intramolecular rotation at the aggregated state. Furthermore, TBFID shows high quantum yield and intense red emission, making the molecule fit for organic light-emitting diodes (OLED) and bioimaging applications.

Large-Scale Mechanochemical Synthesis of Cesium Lanthanide Chloride for Radioluminescence.

Cesium lanthanide chloride (Cs3LnCl6), a recently developed class of lanthanide-based zero-dimensional metal halides, has garnered a significant amount of interest because of its potential applications in scintillators, light-emitting diodes, and photodetectors. Although cesium lanthanide chloride demonstrates exceptional scintillator properties, conventional synthesis methods involving solid-state and solution-phase techniques are complex and limited on the reaction scale. This study presents a facile mechanochemical synthesis method for producing Cs3CeCl6, Cs3TbCl6, and Cs3EuCl6 metal halides on a 5 g scale. These materials exhibit intense blue-violet, green, and red emissions upon ultraviolet excitation, with high photoluminescence quantum yields ranging from 54% to 93%. Furthermore, Cs3CeCl6, Cs3TbCl6, and Cs3EuCl6 metal halides exhibit intense radioluminescence spanning from the ultraviolet to the visible region. This research shows the potential of the scalable mechanochemical synthesis of lanthanide-based metal halides for the advancement of luminescent materials for scintillators.

Intense red emission from trivalent Eu3+ doped Ca9La(VO4)7 nanophosphor for lighting and latent fingerprinting applications

Intense red emission from trivalent Eu3+ doped Ca9La(VO4)7 nanophosphor for lighting and latent fingerprinting applications

Defect level induced negative thermal quenching of β-Ba3LuAl2O7.5: Yb3+, Er3+ phosphor

Temperature-dependent behavior of phosphors has recently attracted significant research attention. This is due to the widespread applications of phosphors. Unfortunately, the thermal quenching effect in many phosphors greatly limits their performance at high temperatures. Herein, negative thermal quenching phosphor β-Ba3LuAl2O7.5: 0.3Yb3+, 0.03Er3+ is synthesized using the high-temperature solid-state method. X-ray Rietveld refinement and EPR results indicate the defect state of oxygen vacancy. Temperature-dependent upconversion luminescence spectra demonstrate that the green and red emission intensities increase with temperature to reach maximums at 398 K and 348 K respectively. Diffuse reflectance spectrum and downshifting luminescence spectrum prove that the defect state is near the 4F7/2 state of Er3+ ions. The defect state traps electrons at room temperature and releases them to populate the 4F7/2 state of Er3+ ion at elevated temperatures to cause the observed thermal enhancement of upconversion luminescence. This material's negative thermal quenching effect makes it a suitable candidate for applications in displays and anti-counterfeiting.

Amplification of intense red emission through integrating Li+ ions to V2O5:Eu3+ phosphors: Optical thermometry, cheiloscopy and extraction of level III features for individual identification

This study presents the synthesis of V2O5:Eu3+ phosphors in concentrations ranging from 1 to 9 mol %, using a solution combustion method with Areca Nut (A.N) as a bio-fuel. The samples exhibit an orthorhombic crystal structure, confirmed by powder X-ray diffraction (PXRD), and rod-like morphology as shown by field emission scanning electron microscopy (FE-SEM). Photoluminescence (PL) studies reveal that the emission intensity of the 5D0→7F2 transition at 619 nm increases with the Eu3+ concentration up to 5 mol %, where it peaks before quenching due to quadruple-quadruple interactions, according to the Van Uitert relation. To improve luminescence, Li+ ions are added, with the V2O5:5Eu3+ co-doped with 4Li+ (V2O5:5Eu3+, 4Li+) ions showing the highest PL intensity, about 5.03 times higher than that of Eu3+ alone. This optimized phosphor has Commission Internationale de l’Eclairage (CIE) chromaticity coordinates of (0.6022, 0.3963), closely matching commercial red-emitting phosphors and demonstrating a colour purity (CP) of 88.69 %. Thermal stability assessments indicate that these phosphors have a high activation energy (Ea) of about 0.224 eV, signifying robust thermal properties. The optimized V2O5:5Eu3+, 4Li+ phosphors efficiently reveal level I–III features in latent fingerprints (LFPs) and accurately identify lip prints (LPs) groove patterns of type I–VI under 365 nm UV light, providing high resolution and contrast. These characteristics make the optimized phosphor an excellent candidate for use in photonic devices, advanced forensic and data security applications.