Photoluminescence Excitation Research Articles

Deep Ultraviolet Excitation Photoluminescence Characteristics and Correlative Investigation of Al-Rich AlGaN Films on Sapphire.

AlGaN is attractive for fabricating deep ultraviolet (DUV) optoelectronic and electronic devices of light-emitting diodes (LEDs), photodetectors, high-electron-mobility field-effect transistors (HEMTs), etc. We investigated the quality and optical properties of AlxGa1-xN films with high Al fractions (60-87%) grown on sapphire substrates, including AlN nucleation and buffer layers, by metal-organic chemical vapor deposition (MOCVD). They were initially investigated by high-resolution X-ray diffraction (HR-XRD) and Raman scattering (RS). A set of formulas was deduced to precisely determine x(Al) from HR-XRD data. Screw dislocation densities in AlGaN and AlN layers were deduced. DUV (266 nm) excitation RS clearly exhibits AlGaN Raman features far superior to visible RS. The simulation on the AlGaN longitudinal optical (LO) phonon modes determined the carrier concentrations in the AlGaN layers. The spatial correlation model (SCM) analyses on E2(high) modes examined the AlGaN and AlN layer properties. These high-x(Al) AlxGa1-xN films possess large energy gaps Eg in the range of 5.0-5.6 eV and are excited by a DUV 213 nm (5.8 eV) laser for room temperature (RT) photoluminescence (PL) and temperature-dependent photoluminescence (TDPL) studies. The obtained RTPL bands were deconvoluted with two Gaussian bands, indicating cross-bandgap emission, phonon replicas, and variation with x(Al). TDPL spectra at 20-300 K of Al0.87Ga0.13N exhibit the T-dependences of the band-edge luminescence near 5.6 eV and the phonon replicas. According to the Arrhenius fitting diagram of the TDPL spectra, the activation energy (19.6 meV) associated with the luminescence process is acquired. In addition, the combined PL and time-resolved photoluminescence (TRPL) spectroscopic system with DUV 213 nm pulse excitation was applied to measure a typical AlGaN multiple-quantum well (MQW). The RT TRPL decay spectra were obtained at four wavelengths and fitted by two exponentials with fast and slow decay times of ~0.2 ns and 1-2 ns, respectively. Comprehensive studies on these Al-rich AlGaN epi-films and a typical AlGaN MQW are achieved with unique and significant results, which are useful to researchers in the field.

A novel red-emitting InScW3O12:Eu3+ phosphor with anti-thermal-quenching performance for high-power WLED applications

A series of red-emitting InScW3O12:Eu3+ (ISWO:Eu3+) phosphors with anti-thermal-quenching performance were successfully synthesized by conventional solid-state reaction. The phase structure and luminescent properties of ISWO:Eu3+ were systematically studied. The photoluminescence excitation (PLE) spectrum showed that ISWO:Eu3+ phosphor can be effectively matched with commercial ultraviolet (UV), violet and blue light chips. The main emission peak of the phosphor was located at 613 nm, which was attributed to the electric dipole transition 5D0 → 7F2. Under the optimal excitation, the prepared ISWO:0.08Eu3+ phosphor showed excellent anti-thermal-quenching performance, its photoluminescence (PL) intensity at 180 °C reached 157.4 % of initial intensity at room temperature. At 465 nm excitation, it also exhibited the anti-thermal-quenching property and the PL intensity remained 115.1 % at 150 °C of that at room temperature. In situ XRD analysis revealed that the lattice contraction resulting in an increase in structural rigidity as the temperature rising, which caused the change of Eu3+ local environment and improved the PL intensity. Finally, a series of warm white LED devices under varying power density conditions with stable output were prepared using the red ISWO:0.08Eu3+ phosphor, indicating that the ISWO:Eu3+ phosphor with excellent anti-thermal-quenching performance has potential application prospects in high-power white light-emitting diodes (WLEDs).

Temperature Dependent Photoluminescence Properties of a Y2Ge2O7:Tb3+ phosphors. A dual band ratiometric luminescent thermometer

A series of green light emitting Y2Ge2O7:xTb3+ phosphors (x = 0.2, 0.5, 1.0, 2.0 and 4.0mol%) were obtained via the solid-state reaction method. The single phase was confirmed by XRD technique. The photoluminescence (PL) excitation spectrum, emission spectra at room and as a function of temperature, decay curves of phosphors were studied in detail. The emission spectra show typical emissions of Tb3+ ions, whose relative intensities change with the ion concentration or UV excitation. A shift of the CIE chromaticity coordinates from blueish to green region was observed. The emission decay curves are compatible with a single type of Tb3+ activator. The obtained internal Quantum Yield (iQY) increase with the terbium concentration, up to 10.0% for sample with 4.0mol%. In addition, the relative sensitivity values (Sr) for samples with 1.0 and 2.0mol% reached 0.97 and 2.02%K-1, respectively. These high thermal sensitivities obtained, in comparison with other Tb3+ based optical temperature sensors, in biophysical temperature range (30–45 °C), illustrates the potential use of Y2Ge2O7:xTb3+ phosphors in the design of efficient FIR luminescent thermometers for biological systems or other industrial applications.

The Role of Ce3+ Co-doping in the Luminescent Enhancement of Bi3+ Emission and Bi3+→Bi2+ Conversion in LiLaP4O12 Host

This work investigates the luminescent versatility of the LiLa(1-x-y)BixCeyP4O12 system as a scintillator material capable of displaying emission in a range from the blue to the red region depending on the Ce3+ concentration. The LiLaP4O12 host has been proven to be useful as a scintillator material when doped with some rare earths and with bismuth ions. However, the process of bismuth valence change induced by X-rays, when inserted in the LiLaP4O12 matrix, is not known to date, as well as whether this can be controlled and used to enhance the luminescence emission. To determine the mechanism of interaction between the Ce3+ and Bi3+ ions in the LiLaP4O12 host, doped and co-doped samples were synthesized and investigated. Identification of crystalline phase was carried out with X-Ray Powder Diffraction. The luminescent properties were studied via photoluminescence emission and excitation using synchrotron radiation. Scintillator features were studied through radioluminescence emission spectrum. The results indicate that Ce3+ transfers either energy or electrons to Bi3+ when excited with UV (5.2 eV) or X-rays, respectively. In the first case, the overall white luminescence is improved, while in the latter, enhanced red luminescence from Bi2+ was observed, indicating the valence change of Bi ions, assisted by Ce co-dopant. A luminescent mechanism, based on the vacuum-referred binding energy model applied to the experimental data, was proposed to explain the Bi2+ emission, deepening the understanding of the Bi emission mechanism and opening the possibility of tailoring the Bi2+/Bi3+ proportion varying the Ce-co-doping concentration.

Optical and EPR study of Mn4+ ions in different crystal environments in Mn, Li co-doped MgO

The influence of Li ion on the symmetry of Mn4+ center and its photoluminescence (PL) in MgO:0,01%Mn, 3% Li ceramics is studied by the X-ray diffraction, electron paramagnetic resonance (EPR), PL and optical absorption methods. It is shown that Li co-doping stimulates conversion of Mn2+ on Mg site into Mn4+ and can decrease symmetry of Mn4+ in a case of their specific close arrangement in the crystal lattice. Two kinds of Mn4+ centers are identified in the EPR and PL spectra: cubic Mn4+ and tetragonal complex Mn4+-Li+. The parameters of corresponding EPR centers are estimated from the experimental spectra (gcub=1.994, |A|cub=70.9x104 cm-1; g1tetr=g2tetr=1.994, g3tetr=1.993, |A|tetr=71x104 cm-1, |D|tetr=220x104 cm-1). The PL lines observed in the low temperature PL spectra are assigned to the specific Mn4+ related centers by using a complementary study of PL excitation spectra and temperature dependent PL spectra. The lines at 654 nm and 671 nm are ascribed to R-line of Mn4+ in a site of cubic symmetry and its phonon overtone, correspondingly, as well as the lines at 666 nm and 681 nm are attributed to R2 line of Mn4+ in site with tetragonal symmetry and to its phonon overtone, correspondingly. It is shown that in Mn doped MgO ceramics made without intentional Li co-doping, the cubic Mn4+ center can be present and contribute to the PL spectra.

Short-Wave Infrared Upconverting Nanoparticles.

Optical technologies enable real-time, noninvasive analysis of complex systems but are limited to discrete regions of the optical spectrum. While wavelengths in the short-wave infrared (SWIR) window (typically, 1700-3000 nm) should enable deep subsurface penetration and reduced photodamage, there are few luminescent probes that can be excited in this region. Here, we report the discovery of lanthanide-based upconverting nanoparticles (UCNPs) that efficiently convert 1740 or 1950 nm excitation to wavelengths compatible with conventional silicon detectors. Screening of Ln3+ ion combinations by differential rate equation modeling identifies Ho3+/Tm3+ or Tm3+ dopants with strong visible or NIR-I emission following SWIR excitation. Experimental upconverted photoluminescence excitation (U-PLE) spectra find that 10% Tm3+-doped NaYF4 core/shell UCNPs have the strongest 800 nm emission from SWIR wavelengths, while UCNPs with an added 2% or 10% Ho3+ show the strongest red emission when excited at 1740 or 1950 nm. Mechanistic modeling shows that addition of a low percentage of Ho3+ to Tm3+-doped UCNPs shifts their emission from 800 to 652 nm by acting as a hub of efficient SWIR energy acceptance and redistribution up to visible emission manifolds. Parallel experimental and computational analysis shows rate equation models are able to predict compositions for specific wavelengths of both excitation and emission. These SWIR-responsive probes open a new IR bioimaging window, and are responsive at wavelengths important for vision technologies.

Excitonic Bose Polarons in Electron-Hole Bilayers.

Bose polarons are mobile particles of one kind dressed by excitations of the surrounding degenerate Bose gas of particles of another kind. These many-body objects have been realized in ultracold atomic gases and become a subject of intensive studies. In this work, we show that excitons in electron-hole bilayers offer new opportunities for exploring polarons in strongly interacting, highly tunable bosonic systems. We found that Bose polarons are formed by spatially direct excitons immersed in degenerate Bose gases of spatially indirect excitons (IXs). We detected both attractive and repulsive Bose polarons by measuring photoluminescence excitation spectra. We controlled the density of IX Bose gas by optical excitation and observed an enhancement of the energy splitting between attractive and repulsive Bose polarons with increasing IX density, in agreement with our theoretical calculations.

Intrinsic process for upconversion photoluminescence via K -momentum–phonon coupling in carbon nanotubes

We investigate the intrinsic microscopic mechanism of photon upconversion in air-suspended single-walled carbon nanotubes through photoluminescence and upconversion photoluminescence spectroscopy. Nearly linear excitation power dependence of upconversion photoluminescence intensity is observed, indicating a one-photon process as the underlying mechanism. In addition, we find a strongly anisotropic response to the excitation polarization, which reflects the intrinsic nature of the upconversion process. In upconversion photoluminescence excitation spectra, three peaks are observed, which are similar to photoluminescence sidebands of the K-momentum dark singlet exciton. The features in the upconversion photoluminescence excitation spectra are well reproduced by our second-order exciton-phonon interaction model, enabling the determination of phonon energies and relative amplitudes. The analysis reveals that the upconversion photoluminescence can be described as a reverse process of the sideband emission linked to the K-momentum phonon modes. The validity of our model is further reinforced by temperature-dependent upconversion photoluminescence excitation measurements reflecting variations in the phonon population. Our findings underscore the pivotal role of the resonant exciton-phonon coupling in pristine carbon nanotubes and present potential for advanced optothermal technologies by engineering the excitation pathways. Published by the American Physical Society 2024

Enhanced Photodetection Performance of WSe2/V2O5 Nanocomposite on Flexible Substrate: Synergistic Advantages and Improved Efficiency.

The two-dimensional (2D) chalcogenide WSe2/V2O5 composite nanostructures were synthesized using the hydrothermal method and extensively characterized with various spectroscopic techniques. X-ray diffraction analysis confirmed the hexagonal crystal structure exhibiting space symmetry of P63/mmc. Scanning electron microscopy images provided insights into the irregular and nonuniform morphology. Optical spectrum analysis indicated a band gap value of 2.01 eV for 15% WSe2/V2O5 nanostructures, as determined by the Wood and Tauc equation. Photoluminescence (PL) excitation spectra at emission wavelengths of 550 and 750 nm exhibited broad emission attributed to self-trapped excitons for V2O5 and WSe2 nanostructures. Under excitation at λexc = 365 nm, PL emission spectra displayed distinct peaks at 550 and 750 nm, demonstrating the ability to emit vivid red light. A device optimized for photoresponsivity (R) of approximately 7.80 × 10-1 A W-1 and detectivity (D) of around 8.65 × 1011 Jones, and quantum efficiency of approximately 3.42 × 10-2 A W-1 were achieved at a wavelength of 390 nm while using a lamination sheet as a substrate. These findings underscore the capability of devices for efficient photoconversion at specified wavelengths, indicating potential applications in sensing, imaging, and optical communication. The photoresponsivity of the device remained stable at 3.38 × 10-3 A W-1 at 0° and 3.09 × 10-3 A W-1 at 55° bending angle. This indicates the resilience of device to mechanical strain, making it ideal for flexible and wearable sensor applications. The structural, morphological, and optical characterizations confirm the suitability of luminescent WSe2/V2O5 chalcogenide for practical optoelectronic applications, especially in display technologies.

Photoluminescence properties of Mn2+-activated red-emitting phosphors with superior thermal stability for backlighting display applications

The red-emitting phosphors, Na2Mg1-x(PO3)4:xMn2+ with concentrations ranging from 0.01 to 0.11, have been successfully synthesized using a simple solid-state method. The as-synthesized phosphors are crystallized in an orthorhombic structure. The luminescence mechanism of Mn2+ ions in Na2Mg(PO3)4 lattice has been deeply explained using the Tanabe-Sugano (T-S) energy level diagram for the d5 electron configuration. The typical photoluminescent emission (PL) and photoluminescent excitation (PLE) spectra were measured. Several excitation peaks in the spectral range of 250–550 nm on the PLE spectrum and a strong emission peak at 613 nm indicate that the as-synthesized phosphors can be effectively excited using ultraviolet (UV) and near-UV LED chips. Several photometric characteristics were measured, such as the Commission International de'LEclarirage (CIE) chromaticity coordinate (x, y), color purity (CP), and correlated color temperature (CCT), corresponding to the concentration-dependent PL spectra. Furthermore, the thermal stability of the Na2Mg1-x(PO3)4:xMn2+ phosphors was investigated through temperature-dependent PL spectra and decay curves from 10 to 500 K. All results confirm that the as-synthesized red-emitting phosphors exhibit excellent thermal stability, which are attractive characteristics for white light emitting diodes (W-LEDs) applications.

Preparation, characterization and emission of Na3-3xLnxFe2(PO4)3 (Ln = Eu, Tb; 0 ≤ x ≤ 0.1 mol %) and photocatalytic activity of Na3Fe2(PO4)3

Rare earth doped compositions Na3-3xLnxFe2(PO4)3 (x = 0, 0.025, 0.05, 0.075 and 0.1) were prepared by ion-exchange method using Na3Fe2(PO4)3 and LnCl3 (Ln = Eu and Tb). Pristine Na3Fe2(PO4)3 was obtained by ethylene glycol assisted gel burning procedure. The phase characterization was performed by powder X-ray diffraction (XRD). All the compositions were well crystalized in monoclinic lattice. The FE-SEM images and elemental mapping were obtained. The infrared and Raman profiles of all-compounds were dominated by the bands owing to the (PO4) units. Investigation on photoluminescence emission and excitation spectra of Ln3+ (Ln = Eu, Tb) were carried out. The excitation spectra of Na3-3xLnxFe2(PO4)3 (Ln = Eu and Tb) gave intensive band at 256 (370) nm for Eu (Tb) doped phosphors. The photoluminescence emission spectra of Ln3+ (Ln = Eu, Tb) were carried out. The emission spectra of these composition were characterized by f -f transitions corresponding to 613 (5D0→7F2) for Eu and 543 (5D4→7F5) for Tb doped compositions. The maximum emission intensity for Eu (Tb) doped phosphors was found at x = 0.075 (0.05). The analysis of CIE and CCT values of all prepared phosphors were also carried out. Decay curves were analyzed in detail. The visible-light photo-catalytic activity of parent Na3Fe2(PO4)3 was examined against decomposition of methylene blue and methyl orange dyes. Parent Na3Fe2(PO4)3 exhibits good efficiency against MB (≈94.5 %) and moderate efficiency against MO (≈64 %) in 180 min of visible light irradiation. Scavengers’ experiments were carried to identify the active species during photodegradation.

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.

Selecting ns2 electron (Sb3+) and d3 electron (Cr3+) co-doped in lead-free halide double perovskite to achieve blue and near-infrared luminescence

The double-perovskite Cs2NaInCl6 has emerged as a highly favored candidate due to its remarkable stability and eco-friendly properties. However, it is noteworthy that this material does not demonstrate the desired optical performance in the crucial visible and near-infrared (NIR) spectrum, which may limit its potential applications in certain domains. We develop such characteristics in Cs2NaInCl6 by co-doping Sb3+ (s-electron) and Cr3+ (d-electron) ions. Doping with Sb3+ allows for 1S0→3P1 transition absorption, which then emits blue photoluminescence of self-trapped exciton (STE). By co-doping Sb3+ and Cr3+ ions, it causes the transfer of excitation energy from STE to Cr3+, yielding strong NIR emission at 950 nm. Temperature-dependent Photoluminescence (PL), PL excitation, PL decay and Tanabe-Sugano diagram provide insight into photophysical processes. Furthermore, a novel dual-modal optical information encryption based on the integration of blue and NIR luminescence printing patterns using Cs2NaInCl6: Sb3+ and Cs2NaInCl6: Sb3+/Cr3+, respectively, is successfully demonstrated.

3D-printed copolymer semi-cavity sensor with inner optical filter-effecting quantum dots photoluminescence for multiple drugs and amino acids detection

Here, we demonstrate a prototype for a novel optical sensor based on 3D-printed copolymer semi-cavity embedded with colloidal ZnCuInS (ZCIS) quantum dots (QDs) and utilizing the optical filter-effect in the QDs photoluminescence excitation pathway by analytes in the solution. First, in situ copolymerization of styrene and n-butyl methacrylate (P(S-BMA)) with colloidal ZCIS QDs allowed formation of solid P(S-BMA) matrix homogeneously impregnated with QDs. Then QDs@P(S-BMA) mixed with polylactic acid (PLA) has been processed into QDs@P(S-BMA)@PLA hybrid filaments using extruder. Then, a semi-cavity optical cell was 3D-printed out of QDs@P(S-BMA)@PLA filaments. Such 3D-printed semi-cavity cell can be used as the optical sensor on various molecules utilizing the optical absorption by analyte molecules through inner filter effect (IFE) of a properly selected QDs excitation beam. The multiple drug and amino acid molecules have been utilized having selective UV absorption to examine our proof of concept.

Effect of Dopant Concentration on Luminescence Properties of Na3Ca2(SO4)3F: RE (RE = Eu3+, Dy3+) Phosphor for Solid-State Lighting.

A fluoride material phosphor doped with rare earth ions Eu3+ and Dy3+ was studied for its photoluminescence (PL) properties. The material was synthesized using a combustion method and characterized using X-ray diffraction (XRD) and PL techniques. The Na3Ca2(SO4)3F: Eu3+ phosphor exhibits two distinct peaks at 593 nm (orange) and 615 nm (red) at an excitation wavelength of 395 nm. The PL excitation spectrum of the Na3Ca2(SO4)3F: Dy3+ phosphor showed series of peaks, corresponding to the 4f → 4f transitions of Dy3+ ions. Under 350-nm excitation, the PL emission spectrum revealed two prominent bands one at 483 nm (blue region) due to the 4F₉/₂ → 6H₁₅/₂ transition, and another at 573 nm (yellow region) resulting from the 4F₉/₂ → 6H₁₃/₂ transition. These blue and yellow emissions suggest potential applications in solid-state lighting, particularly for mercury-free excitation sources. Rare earth-doped Eu3+/Dy3+ materials exhibit highly efficient PL properties, making them suitable candidates for white light-emitting diodes (LEDs) or other solid-state lighting phosphors.

Optical characterization of GaN:Eu microcrystals grown by the ammonothermal method

Eu-doped gallium nitride (GaN:Eu) microcrystals with a wurtzite crystal structure were synthesized using the ammonothermal method. The Eu concentration of GaN:Eu microcrystals estimated by glow discharge mass spectrometry (GDMS) was 5.8 × 1020 atoms/cm3. The morphology of GaN:Eu microcrystals was characterized by scanning electron microscopy (SEM). The exposed crystal faces of GaN:Eu microcrystals were identified as {10−10}, {10−11}, (000−1), and (0001), respectively. The photoluminescence excitation (PLE), photoluminescence (PL) and time-resolved photoluminescence (TRPL) spectra of GaN:Eu microcrystals revealed two luminescent sites of Eu3+ ions, designated as Eu0 and Eu1. The Eu0 was excited in the range of 300 nm to 420 nm, resulting in the observation of four characteristic luminescence peaks at 599 nm (5D0-7F1), 620 nm (5D0-7F2), 632 nm (5D1-7F4), and 663 nm (5D0-7F3). The Eu1 was associated with O2- ions and emitted light at specific excitation wavelengths. The main luminescence peak of the Eu1 was located at 614 nm, accompanied with characteristic peaks at 578 nm, 591 nm, and 698 nm. In view of the distinct luminescence properties of the Eu0 and the Eu1, the energy transfer processes of two luminescence sites were proposed.

Unraveling the photophysical response of BaLaLiTeO6:Dy3+ double perovskites with excellent thermal stability for colour tunable LEDs and optical thermometry

The quest for reliable phosphors has accelerated amidst a growing demand for cost-effective, high-performance multifunctional phosphors. Incorporating thermometric application into double perovskite phosphors can enhance their multifaceted features for diverse applications. The present work endeavours to develop a series of BaLaLiTeO6:Dy3+ double perovskites via a solid-state reaction route, stressing their application in next-generation colour-tunable LEDs and non-contact luminescence thermometry. X-ray diffraction, Raman and FTIR spectroscopy analysis were done to make inferences about the structural modifications induced by the substitution of Dy3+ at the La3+ site of BaLaLiTeO6. An extensive investigation of optical characteristics was carried out by diffuse reflectance spectroscopy, photoluminescence spectroscopy and decay curve analysis. Prominent photometric parameters were also evaluated to assess the commercial feasibility of the developed phosphors in photonic applications. Judd-Ofelt parameters were estimated from the photoluminescence excitation spectra of BaLaLiTeO6:Dy3+ for the first time. Furthermore, the values of radiative parameters, fluorescence decay time and quantum efficiency suggested the suitability of the developed phosphor as a competent material. A comprehensive analysis of BaLaLiTeO6:Dy3+ as a thermographic phosphor was done by temperature-dependent photoluminescence spectroscopy. The potential use of this material in luminescence temperature sensing was probed by estimating the thermometric figures of merit based on the fluorescence intensity ratio (FIR). An absolute sensitivity of 22.17 × 10−4 K−1 was achieved at a temperature of 500 K and a remarkable maximum relative sensitivity of 2.34 %K−1 was attained at 250 K, which is much higher than other Dy3+ substituted thermographic phosphors. All these culminated features of BaLaLiTeO6:Dy3+ phosphor proved their prospective applications in thermally stable colour-tunable LEDs, wLEDs and as non-contact optical temperature sensors.

Structural and luminescence properties of Y2O3:Ho3+ phosphor: Potential applications in plant cultivation LEDs and thermoluminescent dosimetry

Current research on Y2O3:Ho3+ phosphors highlight their promising luminescence properties, but often lacks an environmentally friendly synthesis method and comprehensive analysis of their applications. In this study, we address these gaps by successfully synthesizing Y2O3:Ho3+ phosphors using a green synthesis route with varying concentrations of Ho3+. Our work provides detailed characterization of their photoluminescence (PL) and thermoluminescent (TL) properties. The PL excitation (PLE) spectra reveal a distinct peak at 439 nm, attributed to the 5I8→(5K5; 5G5) transition of Ho3+ions. Upon excitation at 439 nm, the emission spectra show a sharp emission peak around 660 nm from the 5F5→5I8 transition, with the 0.1 mol% Ho3+ phosphors exhibiting particularly strong red emission, indicating their suitability for indoor plant cultivation under LED lighting. Additionally, TL properties were evaluated after gamma-ray exposure, with the highest emission intensity at 0.1 mol% Ho3+ concentration. TL glow curves were analyzed for various radiation doses using the Computerized Glow Curve Deconvolution (CGCD) method, and TL trapping parameters were determined through Chen's peak shape and the Initial Rise methods. This work demonstrates significant potential for using these phosphors to enhance indoor plant growth and for applications in thermoluminescent dosimetry (TLD).

The luminescent behaviors and J-O theory analysis of red phosphor Ca1-xGeO3:xEu3+

The luminescent material Eu3+-doped CaGeO3 has been synthesized using a high-temperature solid-state reaction technique. The crystal structure was analyzed using X-ray diffraction (XRD). The results showed that the samples belonged to the triclinic crystal system with the space group P1̅. The luminescent properties including photoluminescence excitation (PLE), Photoluminescence emission (PL) spectra, and lifetime, thermal stability, and diffuse reflectance spectroscopy (DRS) have been investigated. Under near-ultraviolet excitation at 390 nm, the phosphor emits red light with the highest intensity around 611 nm, which is dominated by the 5D0→7F2 electric dipole transitions. It indicates that Eu3+ is in the inversion center of the crystal. The concentration quenching occurs at about 6 % doping from the concentration-dependent luminescence behavior. The energy transfer mechanism was analyzed to be mainly the energy transfer between neighboring ions. The thermal stability was 82.16 % at 423 K. The chromaticity coordinates are in the red area and the color purity approaches 99 %. Furthermore, the J-O theoretical results are used to confirm the experimental result. It suggests that Ca1-xGeO3:xEu3+ is an effective red luminescent material for illumination and backlight display applications.

Photoswitchable AIE‐Active Supramolecular Self‐Assemblies for Biosensing and Bioimaging

Photoswitchable fluorescent self‐assemblies exhibiting aggregation‐induced emission (AIE) properties have garnered widespread attention. Due to their great adaptiveness and responsiveness towards different wavelengths required by photoreaction, photo‐isomerization, and photoluminescence excitation, these fluorescent self‐assemblies show diverse emission behavior in a spatial, temporal, and polychromatic manner. Integrating organic photoswitches and AIE fluorophores, these photoluminescent nano‐assemblies has been proven to be an effective approach, allowing the development of sophisticated systems for drug release and cell regulation that can be precisely manipulated through light or other stimuli. This review systematically encapsulates recent advances in photoswitchable fluorescent self‐assemblies under multi‐scenario biological applications. The construction of photoswitchable AIE fluorophores through covalent and non‐covalent interactions and their multimodal regulation are detailed, along with their biological applications in biosensing, bioimaging, and drug therapy.