Phosphor Samples Research Articles

A novel highly thermally stable phosphor powder Ba2LuSbO6: Eu3+ for latent fingerprint visualization

In modern forensic science, fingerprints are critical evidence due to their uniqueness and difficulty to replicate. However, it is challenging to observe and identify some latent fingerprints (LFP), because alternative processing methods for recognition are often required. The use of Eu3+-doped phosphors, which emit red-orange light, presents an effective approach for enhancing the visibility of LFP. Eu3+-doped Ba2LuSbO6 (BLSO) phosphors were synthesized using a high-temperature solid-state method, aiming to improve the recognition of LFP for enhanced fingerprint identification. The phase structure of the fluorescent powder samples was analyzed through X-ray diffraction (XRD) combined with Rietveld refinement, as well as scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Photoluminescence spectra of Ba2LuSbO6: xEu3+ phosphor samples exhibit orange-red emission peaks at 595 and 618 nm when excited by 250 nm deep ultraviolet light. Concentration quenching is observed at a doping concentration of 20 mol%. The Ba2LuSbO6: 0.2Eu3+ phosphor sample demonstrates exceptional thermal stability, with value of 92.50% at 423 K. The quantum efficiency of the Ba2LuSbO6: 0.2Eu3+ phosphor sample was evaluated using an integrating sphere, yielding an IQE of 79.34%. In order to visualize latent fingerprints (LFPs), hydrophilic BLSO: 0.2Eu3+ phosphors were transformed into hydrophobic BLSO: 0.2Eu3+@OA phosphors through a coating of oleic acid (OA). The BLSO: 0.2Eu3+@OA phosphor proves capable of generating dependable LFP fluorescence images with superior contrast and resolution. These findings underscore the significant potential for application of BLSO: 0.2Eu3+ products LFP visualization.

Optimization of upconversion luminescence performance and temperature sensing characteristics of Sr0.37Ba0.50Al2Si2O8:Ho3+, Yb3+ phosphors based on a cation substitution strategy

Upconversion luminescent (UCL) materials have broad application prospects in the field of temperature sensing; thus, improving the luminescence performance and temperature measurement sensitivity of upconversion phosphors is highly important. In this study, SrAl2Si2O8 with good thermal stability was doped with Ho3+ and Yb3+, and the optimal concentration was determined to be SrAl2Si2O8:1%Ho3+, 12%Yb3+ (in mole fraction). A series of (Sr0.87‒xBax)Al2Si2O8:1%Ho3+, 12%Yb3+ phosphor samples was prepared by using a cationic substitution strategy and further doping Ba2+ to replace the Sr2+ lattice in the matrix. The results show that the introduction of Ba2+ effectively replaces Sr2+ and significantly increases the upconversion fluorescence emission intensity of SrAl2Si2O8:1%Ho3+, 12%Yb3+ by approximately 2.9 times. The temperature sensing properties of SrAl2Si2O8:1%Ho3+, 12%Yb3+ and Sr0.37Ba0.50Al2Si2O8:1%Ho3+, 12%Yb3+ were investigated. The Ho3+-based 5F5 and 5S2/5F4 nonthermal coupled energy level fluorescence intensity ratio (FIR) techniques in the Ba0.37Sr0.50Al2Si2O8:1%Ho3+, 12%Yb3+ phosphors show a maximum temperature measurement absolute sensitivity of 4.32%/K at 573 K and a maximum relative sensitivity of 1.08%/K at 373 K; these values are 5.8 and 3.2 times greater, respectively, than that of the non-Ba2+-doped SrAl2Si2O8:1%Ho3+, 12%Yb3+ phosphor. These results not only confirm the effectiveness of the cation substitution strategy in enhancing the upconversion luminescence performance and temperature sensing characteristics but also provide a scientific basis for the design of high-performance optical temperature sensors.

Synthesis and thermoluminescence characterization of Ba₆Y₂W₃O₁₈ perovskite nanosensors for dosimetry

Through the citrate-assisted sol-gel method, barium gadolinium tungstate (Ba6Y2W3O18) perovskite samples were synthesized, and their luminescence properties were investigated. Through X-ray diffraction (XRD) the crystal structure of the prepared samples was examined. The tunnelling electron microscopy (TEM) analysis has confirmed the agglomeration of the nanoparticles into rods with an average diameter and length of 71 and 214 nm, respectively. The thermoluminescence (TL) properties were investigated by; first, estimating the number of composing TL components using both experimental and computational methods; second, studying the dose-response of the glow curves in response to the irradiated beta dose. The third step in the study of the TL properties was to assess the reusability of the prepared samples in TL dosimetry and the fourth step was to estimate the minimum detectable dose of the phosphor samples. The Computerized Glow Curve Deconvolution (CGCD) method was then used to extract the kinetic parameters of the composing TL peaks.

Multifunctional BiOCl: Sm3+ nanophosphors: A luminescent platform for solid-state lighting applications, optical thermometry, photocatalytic and forensic applications

Rare-earth-activated phosphor materials have been widely used as active probes in optical materials for multidimensional applications. Here, we report a series of ultrahigh purity orange-red emitting BiOCl: xSm3+ (x = 0.5- 2.5 mol %) nanophosphors synthesized via conventional solid-state method at relatively low temperatures for various photonic and forensic applications. XRD and Rietveld refinement results confirmed the tetragonal crystal structure of the synthesized phosphor materials with space group P4/nmm. Fourier transform infrared (FT-IR) and Raman spectroscopy were used to perform the functional group analysis. The UV–Vis–NIR spectra were analyzed to determine the Judd-Ofelt (JO) intensity parameters (Ω2, Ω4, Ω6) and to identify the bonding structure and spontaneous emission properties of the samples. The prepared phosphors exhibit intense orange-red emission under 408 nm excitation and beyond 1 mol% doping of Sm3+ ions, the emission intensity decreases due to concentration quenching mechanism via, dipole-dipole interaction between the optically active Sm3+ ions in the phosphor sample. The synthesized BiOCl: Sm3+ nanophosphors possess low correlated color temperature (CCT), admirable high color purity (99.4 %) and outstanding internal quantum efficiency (IQE) of 95.27 %. The optical thermometry behavior of the optimized sample has been investigated in detail. Moreover, the optimized nanophosphor stains on porous and non-porous surfaces show clear ridge patterns with high sensitivity, efficiency, and minimal background hindrance for latent fingerprints and lip print detection in forensic applications and are used as security ink in anti-counterfeiting applications. Overall, the results revealed the potential prospects of BiOCl: Sm3+ nanophosphors in the field of display applications, optical thermometry, and forensic sciences.

Efficient Energy Transfer for Near-Perfect Quantum Efficiency and Thermal Stability.

The pursuit of high-quality phosphors exhibiting swift response to near-ultraviolet (n-UV) excitation, elevated quantum efficiency (QE), superior thermal stability, and impeccable light quality has been a focal point of investigation. In this research, we synthesized a novel K2La2B2O7:Ce3+,Tb3+ (KLBO:Ce3+,Tb3+) color-tunable phosphor that meets these requirements. KLBO:Ce3+ can be stimulated efficiently by the n-UV light and shows an intense blue emission centered at 437 nm. Notably, KLBO:0.04Ce3+ exhibits exceptional internal QE (IQE = 94%) and outstanding thermal stability (I423K/I303K = 88%). Optimization of doping compositions enables efficient Ce3+ → Tb3+ energy transfer, resulting in substantial enhancements in QE and thermal stability. Specifically, KLBO:0.04Ce3+,0.28Tb3+ achieves an IQE of 98% and a thermal stability of 97%, higher than those of most phosphors of the same type. White light-emitting diodes fabricated using phosphor samples emit warm white light characterized by high Ra (Ra = 96.6 and 93.4) and low CCT (CCT = 4886 and 4400 K). This study underscores the feasibility of enhancing phosphor QE and thermal stability through energy transfer mechanisms.

Upconversion, downshifting, quantum cutting and back energy trasfer from Yb3+ to Er3+ in Er3+/Yb3+ co-doped CaTiO3 phosphor, intense NIR generation for communication

The perovskite based phosphor materials are widely used to increase the efficiency of solar cells. In this work, Er3+ doped and Er3+/Yb3+ co-doped CaTiO3 perovskite phosphor samples have been synthesized by solid state reaction technique at 1473 K. The phosphor samples show orthorhombic phase with Pnma (62) space group. The average crystallites and particles size of CaTiO3 are increased in presence of Er3+ and Yb3+ ions. Er3+ doped CaTiO3 phosphor samples give downshifting emission under 379 nm excitation. Though upconversion emission is seen in Er3+ under 980 nm excitation without Yb3+ ions in this host. The emission intensity of Er3+ ion is enhanced by 46 and 16 times for green and red emissions, respectively in presence of Yb3+. An intense quantum cutting (QC) emission is observed at 980 nm in presence of Yb3+ in CaTiO3:0.5Er3+ phosphor under 379 nm excitation. The QC efficiency has been found to be 119 % for CaTiO3:0.5Er3+/5 Yb3+ phosphor. Further an interesting phenomenon of back energy transfer (BEnT) from Yb3+ to Er3+ giving an intense NIR emission from Er3+ at 1002 and 1550 nm have been observed. The phosphor sample also shows an intrinsic optical bistablity (IOB) by upconversion. Thus, the prepared phosphor samples may be useful to increase the efficiency of c-Si solar cell, NIR emission for communication, bistable material and green light emitting source.

Structural, optical, and the effect of beta source (90Sr/90y) radiation on the thermoluminescence properties of the transition metal activated on lithium aluminum borate phosphor (Li3Al3(BO3)4:Mn)

The activation of Lithium aluminum borate material with varying concentrations of transition metal of manganese was studied. The synthesis of the phosphor samples was achieved by employing the solid-state sintering technique. The study aimed to determine the structural property, optical property, and the effect of beta source (90Sr/90y) radiation on the thermoluminescence properties of the phosphor material. The analyzed structure of both doped and undoped samples was obtained to be from 52.17 to 67.13 nm as the crystallite size and 67.00–120.00 nm as the particle size respectively. The optical studies showed an increase in mole concentration of the doped samples resulted in an increase in absorbance and a decrease in the energy band gap from 4.45 to 4.00 eV. The thermoluminescence report measured showed that the Mn-doped sample on lithium aluminum borate has the most prominent peak at 78 °C (major peak) and 294 °C (minor peak) when exposed to radiation dose (90Sr/90y beta source) of 50 Gy. The acquired activation energy was resolved using some of the models which include the initial rise, deconvolution, and the heat rate techniques. The dose response was determined to be linear from the Mn-doped lithium aluminum borate.

Synthesis and erudite insight into the structural, luminescence and thermal sensing characteristics of Sm3+ incorporated [formula omitted]-BaB2O4 novel phosphors

In this paper, we have presented the comprehensive characterization of red-light-emitting novel β-BaB2O4:xSm3+ (x = 0.5, 0.75, 1, 1.5, and 2 mol%) phosphor samples synthesized by making use of solid-state reaction method. The XRD patterns verified the successful synthesis and in-depth analyses were carried out to explore the structural, luminescence, and thermal properties. Notably, the introduction of Sm3+ through doping did not result in any substantial alterations in the crystal structure. Photoluminescence (PL) emission spectra exhibited 4 distinct peaks for 401 nm excitation. Out of these 4 peaks, the prominent peak was present at 601 nm, attributed to the magnetic dipole-allowed transition 4G5/2 → 6H7/2. The colorimetric analysis revealed the correlated color temperature (CCT) to be around 1700 K, accompanied by 99.9 % colour purity. The optimal doping concentration, before luminescence quenching, was identified as 1 mol%, with multipole-multipole interactions identified as the predominant quenching mechanism. Diffuse reflectance spectroscopy (DRS) studies on β-BaB2O4:1%Sm3+ confirmed characteristic peaks corresponding to Sm3+ transitions, revealing an ionic bonding nature between Sm3+ and the host. Also, the direct optical band gap was determined to be 5.62 eV. Furthermore, the optimized phosphor demonstrated exceptional temperature-dependent photoluminescent (TDPL) properties, exhibiting a negligible (∼5 %) decrease in emission intensity for prominent peaks even at 440 K. Overall, the phosphors displayed high activation energy, significant thermal stability, and thermal sensing properties, making them promising candidates for various optoelectronic applications.

Spectral studies of thermally stable Dy3+/Sm3+ co-doped Li2Ba5W3O15 phosphors for warm white LEDs

In the current study, a series of Li2Ba5W3O15: RE3+ (RE = Dy, Sm) [LBW:Dy3+/Sm3+] phosphors were prepared using a high-temperature solid-state method. X-ray diffraction, Scanning electron microscopy with energy-dispersive x-ray analysis scans showed that the crystal form was consistent with the standard LBW and comprised small irregularly shaped particles. Diffuse reflectance spectral (DRS) data was utilized to calculate the band gaps. Fluorescence study shows that LBW material doped with Dy3+ and Sm3+ yield distinct colors at 496 nm (blue) for Dy3+ and 582 nm (green-yellow), 612 nm (yellow), and 669 nm (red) for Sm3+ when excited by near-ultraviolet (336 nm) light. The observation of energy transfer between Dy3+ and Sm3+ ions play a role in modifying the luminescence of LBW:Dy3+/Sm3+ co-doped phosphors. With a constant excitation wavelength (λ Ex), different levels of activator doping lead to a change in the emission colors from their neutral white light to a deep orange-red region for LBW:Dy3+/Sm3+ phosphors. The decay curves demonstrate a decrease in lifetime with an increase in the concentration of activator ions (Sm3+). For D3S5 phosphor, the temperature-dependent photoluminescence characteristics were analyzed under λ Ex = 336 nm excitation. The results indicate excellent luminescence thermal stability with an activation energy of 0.16 eV at λ Ex = 336 nm. With its low color-correlated temperature and good thermal stability, the prepared phosphor sample shows potential as a solid-state emitting phosphor that can be used with UV chip stimulation for warm white LED applications.

Rapid detection and recognition of phosphors using laser-induced breakdown spectroscopy and principal component analysis method—back propagation neural network algorithm

Rapid detection and quality monitoring of phosphor materials have always been a difficult problem in phosphor materials market. In this work, an independently proposed method based on principal component analysis method—error back propagation neural network algorithm—laser induced breakdown spectroscopy (PCA-BPNN-LIBS) was used for the detection and recognition of phosphors. Firstly, spectroscopic study was carried out on phosphor material samples, and the composition of phosphor elements was analyzed according to the full emission spectrum. Spectral data with different element characteristics detected by LIBS were used as training data sets for further identification. Then PCA method and BPNN algorithm were applied to identify 4 types phosphor samples (P11, P20, P43, P46). A very clear distinction graph was obtained, and the classification accuracy of 99.93% was verified. Allresults show that the proposed PCA-BPNN-LIBS method is an effective method for rapid analysis and recognition of phosphors.

The influences of LaVO4:Eu3+,Cr3+ red phosphors on white light-emitting diode applications

<span>In this present paper, the </span><span lang="EN-ID">LaVO<sub>4</sub>:Eu<sup>3+</sup>,Cr<sup>3+</sup> (</span><span>LV:Eu,Cr) </span><span lang="EN-ID">red-orange phosphors</span><span>are introduced in WLED fabrication. The LV:Eu,Cr phosphor is synthesized with high-temperature solid-phase reaction</span><span lang="IN">.</span><span> The luminescence properties of the phosphor are monitored with ultraviolet-visible and near-infrared (UV-vis-NIR) measurements. The heat generating in the phosphor sample is also investigated with different power densities of the 980 nm laser. The phosphor exhibits absorption bands at 254 nm and 316 nm, suitable for UV light-emitting diodes (UV LED) applications. The Cr<sup>3+</sup> concentrations have noticeable effects on the luminescence of the phosphor. The increasing Cr<sup>3+ </sup>dosage initiates reduction in Eu<sup>3+</sup> emission intensity and luminescence lifetime average. The heat-activated amount in the phosphor is also significant with the higher concentration of Cr<sup>3+</sup> ions. When using the LV:Eu,Cr phosphor in white light-emitting model (WLED), the dominant red-orange emission centered at 595 nm is observed, in addition to the blue peak at 453 nm. The luminosity, color rendition, and color uniformity of the WLED light are also discussed. The findings indicate that the phosphor can be combined with other high-efficiency blue and green phosphors to obtain the improved color rendition and luminous performances and used in heat-creating optical applications.</span>

Study of energy transfer process and radiative properties of CaAl4O7:Ho3+ phosphor for green light emission

This work comprehensively analyse the structural and photoluminescence properties of Ho3+-doped CaAl4O7 phosphor systems. X-ray diffraction (XRD), diffuse reflectance spectrum (DRS), photoluminescence (PL), and Fourier transform infrared (FT-IR) spectroscopy measurements were carried out, and Rietveld analysis confirmed the pure monoclinic structure of CaAl4O7:Ho3+ phosphor. The FT-IR spectrum showed absorption bands for the tetrahedral sites of the Al-O bonds and the octahedral sites of the Ca-O bonds, which indicate the formation of the CaAl4O7:Ho3+ phosphor. The diffuse reflectance spectrum shows sharp peaks in the visible and near-infrared regions. Photoluminescence excitation (PLE) measurements were performed on all the phosphor samples by monitoring emissions at 545 nm. Radiative properties such as total radiative transition probabilities (AT), radiative lifetime (τ rad), and branching ratios (β) are reported by Judd–Ofelt analysis and PLE spectral measurements. Upon 454 nm excitation, a green emission band is observed at around 545 nm (5F4 + 5S2 → 5I8), and these results indicate that x = 0.05 mol Ho3+ is the optimum concentration as the 5F4 + 5S2 → 5I8 emission intensity reaches its maximum. The emission intensity quenching and energy transfer mechanism are discussed, and the results suggest that the CaAl4O7:Ho3+ samples are suitable for green-emitting phosphor.

Stimulus response of mechanoluminescence of SrAl2O4:Eu,Dy mixed with epoxy resin using uniaxial load

This paper reports the mechanoluminescence (ML) stimuli by a uniaxial load on rectangular-shaped molded SrAl2O4:Eu,Dy phosphor mixed with epoxy resin. The Sr0.97Al2O4: Eu0.01, Dy0.02 phosphor has been prepared through a solid-state reaction technique in the reducing atmosphere created through activated charcoal. The XRD pattern of this phosphor confirms its monoclinic structure. When a load is applied on the rectangular-shaped (RS) molded ML sample, the stimuli ML intensity initially increases with time, attains a peak value, and then decreases with time. It has also been found that the peak ML intensity of the phosphor is linearly proportional to the increasing applied loads. A minute change in tm of the phosphor sample with increasing loads has been recorded. The ML intensity increases with the thickness of the RS molded phosphor samples. The peak of photoluminescence (PL) spectrum of the prepared phosphor excited with 345nm wavelength of light is found at 518 nm.

A single phase Li2Ba5W3O15:Dy3+/Eu3+ phosphor for color tunable devices and non-contact optical thermometry

A set of warm white phosphor samples Li2Ba5W3O15 (LBW):xDy3+, yEu3+ were prepared via a high-temperature solid-state process. Field emission scanning electron microscopy (FE-SEM) and Energy-dispersive X-ray analysis (EDX) with X-ray diffraction (XRD) are the structural analyses that show the incorporation of Dy3+ and Eu3+ ions into the LBW host matrix, without causing any damage to the lattice structure. Fourier Transform Infrared Spectroscopy (FT-IR) approves the presence of distinct vibrational characteristics of the proposed phosphors. The band gaps of the prepared phosphor samples were determined using diffused reflectance spectral (DRS) data. The energy transfer between Dy3+ and Eu3+ ions was observed, contributing to the adjustable luminescence of the LBW:Dy3+/Eu3+ phosphors. By varying the activator doping levels while keeping the excitation wavelength constant, the emission colors of LBW:Dy3+/Eu3+ phosphors shift from natural white with negligible color purity to a relatively pure orange-red region. The decay curves follow the bi-exponential behavior of decreasing lifetime with increasing concentration of the activator ions. A temperature measurement model using fluorescence intensity ratio (FIR) was developed using D3E0.75 phosphor demonstrating excellent optical temperature measurement properties, with a maximum value of Sr (=0.97 % K−1). Therefore, all the experimental results indicate that the prepared Dy3+/Eu3+ co-doped LBW phosphors can be a suitable choice for UV-excitable warm white lighting devices with color tunability and non-contact optical thermometry measurements.

Effect of annealing conditions on the luminescence properties and thermometric performance of Sr3Al2O5Cl2:Eu2+ and SrAl2O4:Eu2+ phosphors.

We report on the synthesis, photoluminescence optimization and thermometric properties of Sr3Al2O5Cl2:Eu2+ and SrAl2O4:Eu2+ phosphor powders. The photoluminescence of Sr2.9Al2O5Cl2:0.1Eu2+ phosphors exhibits a blue-shift with an increasing annealing temperature owing to a decrease in the crystal field strength of the host caused by evaporation of Cl from the material. The quenching of the blue band in favour of the red band observed in the luminescence spectra of Sr2.9Al2O5Cl2:0.1Eu2+ with an increased annealing temperature was explained using the mechanism of the Landau-Zener transitions. The quantum yield and the lifetime of the phosphors depend on the annealing temperature. Phosphor samples annealed at 850 °C, 1000 °C, 1200 °C and 1500 °C were found to be potential luminescence thermometers using the luminescence spectral method. For Sr3Al2O5Cl2:Eu2+ annealed at 1000 °C, the temperature-dependent dual-band intensity ratio demonstrated a high-temperature sensitivity of ∼1.47%/°C in the temperature range of 23 °C to 40 °C which is superior to other reported phosphors with a microsecond decay time, suggesting that the material has potential for sensitive thermometry applications at ambient temperatures.

Structural, photoluminescence and energy transfer investigations of novel Dy3+ → Sm3+ co-doped NaCaPO4 phosphors for white-light-emitting diode applications.

In this study, Dy3+-doped and Dy3+/Sm3+ co-doped NaCaPO4 white-emitting polycrystalline phosphor samples were synthesized using a solid-state reaction method. The samples were characterized by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Field-emission scanning electron microscopy (FE-SEM), and Photoluminescence (PL) analysis. The phase purity characterization and crystal structural analysis were done using the Rietveld refinement-based FullProf Suite software. The Rietveld refinement result confirms single-phase formation for both Sm3+ and Dy3+/Sm3+ co-doped NaCaPO4 samples with an orthorhombic structure and with a monotonic change in lattice parameters with doping. The PL studies of the Dy3+-doped samples revealed two emission bands. However, at 352 nm, the Dy3+/Sm3+-co-doped samples revealed distinctive emission bands for both ions. The emission peaks at 480 nm (blue) and 573 nm (yellow) are related to the 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 transitions of Dy3+ ions; however, the emission peaks at 600 nm and 647 nm are attributed to the 4G5/2 → 6H7/2 and 4G5/2 → 6H7/2 transitions of Sm3+ ions. The intensity of the Dy3+ emissions decreased as the Sm3+ levels increased but the emission intensity of the Sm3+ ions increased. The co-doping of Sm3+ ions in Dy3+-doped phosphors results in unique characteristics due to the energy transfer (ET) from Dy3+ → Sm3+ ions. The effectiveness of this ET from Dy3+ → Sm3+ ions is positively correlated with the dopant amounts of the Sm3+ ions. The interaction mechanisms have been identified as dipole-dipole based on Dexter's energy transfer and Readfield's approaches. All decay curves can be adequately fitted via bi-exponential functions, suggesting the movement of energy between Dy3+ → Sm3+ ions. Temperature-dependent PL measurements and CIE color coordinate analysis reveal excellent luminescent properties, making these Dy3+/Sm3+ co-doped phosphors advantageous for white light-emitting diode (WLED) technologies.

Europium-doped strontium gadolinium oxide phosphor: Investigating structural and photoluminescence characteristics via sol-gel combustion synthesis

SrGd2O4 phosphors doped with Eu3+ were successfully synthesized through a sol-gel combustion method, covering a range of dopant concentrations from 0.25 mol% to 3 mol%. The structural analysis of these phosphor materials was comprehensively conducted utilizing various techniques, including X-ray powder diffraction analysis (XRD), Energy Dispersive X-ray (EDX), and Fourier-transform infrared spectroscopy (FTIR). In addition to unveiling the structural characteristics, these analyses provide valuable insights into the compositional aspects, enhancing our understanding of the synthesized SrGd2O4:Eu3+ phosphors across different doping levels. XRD analysis findings validate the successful generation of the intended SrGd2O4 host, demonstrating orthorhombic system structures consistent with JPCD card number 98-019-3592. FTIR analyses conducted on the phosphor samples not only identify bending modes but also reveal intricate details about small vibration bonds within the material. When excited by the 349 nm laser, SrGd2O4:xEu3+ phosphors exhibit distinct photoluminescence (PL) properties like red emission at 614 nm from Eu3+. From the emission spectra, one can clearly observe that Eu3+ with an ionic radius close to the Gd3+ ion preferentially occupies the symmetry sites of the host lattice. The optimal doping concentration was determined to be 0.5 mol%, as revealed by the data in our study. Additionally, a deeper understanding of the luminescence quenching mechanism was attained, pinpointing the involvement of dipole-dipole (d-d) energy transfer in this intriguing phenomenon. This optimal concentration not only enhances the material's properties but also underscores the pivotal role of d-d interactions in governing the luminescence behavior within the doped system.

Development of NaY9Si6O26:Yb3+ Phosphor with High Thermal Stability and Its Crystals Structure and Luminescent Properties for NIR Anti-Counterfeiting

Near-infrared (NIR) radiation has attracted considerable industrial and research interest. NIR emission has promising potential for varied applications, mostly related to the characterization of chemicals, security, pharmaceutical, medical, cosmetic, food, and agricultural industries, which contribute to the advancement of modern technology. Emission sources such as tungsten halogen lamps, light emitting diodes (LEDs) and phosphor converted LEDs (pc-LEDs) can emit in the infrared range. Among these, NIR pc-LED is considered as the most suitable emission source because it provides adequate emission, high efficiency, long lifetime and excellent durability. In recent years, studies have been conducted to adjust the emission spectrum suitable for NIR phosphors and to improve quantum efficiency in order to apply them to advanced applications and devices of pc-LEDs.Recently, it is necessary to develop a material capable of specifying the near-infrared emission wavelength of near-infrared excitation beyond ultraviolet excitation infrared for advanced anti-counterfeiting against advanced counterfeiting technology. In the present study, a rare-earth-containing compound doped with an activator was used as a host system for a near-infrared phosphor to develop suitable luminescent properties. Yb3+-doped NaY9Si6O26 phosphors were synthesized using a conventional solid-state reaction method. The main phase of the synthesized phosphor samples exhibited a hexagonal structure NaY9Si6O26 phase, and had an angular-shape with an average grain size of 1-3 μm. The NaY9Si6O26:Yb3+ phosphors showed a broad near-infrared emission from 950 to 1100 nm, which was attributed to the 2F5/2 → 2F7/2 transition of Yb3+ ions under 270 and 920 nm excitation. The excitation spectra, recorded by monitoring the emission at 985 nm, showed two bands in the ultraviolet and infrared regions The excellent thermal stability of NaY9Si6O26:Yb3+ phosphor was evident from the fact that the relative PL intensity of NaY9Si6O26:Yb3+ phosphor was 82% of the initial PL intensity at 300 °C, and the thermal degradation was negligible after cooling. These results suggest NaY9Si6O26:Yb3+ phosphors are promising next-generation candidates for advanced anti-counterfeiting applications.

Combustion synthesized La2O3: Er3+/Yb3+ phosphor for simultaneous upconversion emission and photo-thermal signal generation

The Er3+/Yb3+ doped La2O3 phosphor is prepared through combustion synthesis route and then studied using frequency upconversion (UC) and photoacoustic spectroscopic techniques. Prepared phosphor sample was annealed at high temperature ∼2100°C for short time and then structural and optical characterizations were performed. A photoacoustic cell was fabricated to record photoacoustic signal generation. Samples have shown strong upconversion emission at 409 nm, 523 nm, 548 nm, and 672 nm due to the 2H9/2 →4I15/2, 2H11/2 →4I15/2, 4S3/2 → 4I15/2 and 4F9/2→ 4I15/2 transitions, respectively. The photoacoustic measurement has revealed that heat generation in the sample increases in line with the increase in upconversion emission although both properties are opponent to each other. Studies show that prepared phosphor is efficient for generating strong upconversion emission as well as strong photoacoustic signal (also photo-thermal signal) and hence present dual functional sample seems useful for upconversion imaging as well as photo-thermal therapy.

Achieving Multicolor Emitting of Antimony-Doped Indium-Based Halide Perovskite via Monovalent Metal Induced Phase Engineering.

Lead-free metal halide perovskites have attracted attention because of their excellent optical properties and nontoxicity. Here, we report the synthesis of Sb3+-doped indium halide perovskite Cs2InCl5·H2O:Sb3+ by an improved solution coprecipitation method. The treatment of the Sb3+-doped indium halide perovskite with selected monovalent cation halides led to Cs2MInCl6 (Ag+, K+, Na+) in different crystal structures or phases. Sb3+ has an isolated ns2 electron, and Sb3+-doped metal halide acts as the luminescence center and exhibits bright broadband emission that originated from self-trapped excitons. Under UV light excitation, these phosphors with different crystal structures emitted multicolored luminescence ranging from blue, green, yellow, and red depending on whether or not or which monovalent metal ion was used. The phosphor samples were used to print high-resolution 2D color barcodes for security and anticounterfeiting applications. The study presented here provides a new approach for the design and synthesis of lead-free metal halide perovskites with different crystal structures and unique optical properties.