Thermostimulated Luminescence Research Articles

Trap engineering in bismuth activated NaLu(Gd)GeO4 persistent phosphors by doping Ln3+

Persistent phosphors, as a promising material for information storage and encryption, have garnered considerable attention owing to their rapid access and low-energy consumption. However, the lack of effective trap control in storage phosphors has resulted in limited storage capacity. In this study, we have prepared a series of NaLu(Gd)GeO4:Bi3+,Ln3+ (Ln = Eu, Tb, Dy, Pr, Sm, Er, Nd, Ho, Tm, and Yb) materials exhibiting tunable multimode and multicolor stimuli-responsive luminescence. The enhanced thermo-stimulated luminescence of five times is obtained in NaLuGeO4:Bi3+,Eu3+ relative to NaLuGeO4:Bi3+, where Bi3+ not only serves as the luminescent center but also as the hole trap center, and trace amounts of Eu3+ act as electron traps to form stable electron-hole pair traps together with Bi3+ hole traps. We propose a new method to improve trap density by constructing electron-hole pair traps via utilizing Bi3+ and Ln3+ as both trap makers and luminescence centers. Density functional theory calculations provide detailed information on the band structures of the matrix and electronic properties, which has confirmed the types of traps and then supports persistent luminescence mechanisms. Particularly, our phosphors are used as optical storage medium for multilevel optical data recording in a single physical layer through managing traps via setting the temperature. This study provides valuable insights for the design and fabrication of next-generation optical information storage and encryption materials.

Heterovalent Co‐Doped LiLuF4 Composite Flexible Films as Persistent Luminescence Scintillator for X‐Ray High‐Resolution Extension Imaging

AbstractScintillators with high light yield, spatial resolution, and detection sensitivity are desirable for X‐ray imaging. Howerer, it remains challenging to improve the light yield and radiation detection capability of alkali metal rare‐earth fluoride (ALnF4). Herein, a type of Cu2+ ion heterovalent co‐doped LiLuF4:Tb,Cu microcrystalline scintillation material with high light yield, persistent, and thermostimulated luminescence is obtained by defect engineering. The heterovalent codoping strategy not only increases the radioluminescence (RL) intensity, but also introduces more carrier traps in the material to enhance the long‐afterglow and thermoluminescence intensity of LiLuF4:Tb microcrystals. After doping of 3 mol% Cu2+ ions, the RL efficiency is increased by 88.61%, and the X‐ray detection limit of LiLuF4:Tb,Cu reaches 2.7928 nGy·s‒1. This detectivity is considerably lower than the medical imaging requirements (5.5 µGy·s‒1). Furthermore, a large‐area flexible scintillation film of dimensions 30 × 30 cm2 is prepared to achieve high spatial resolution X‐ray imaging of 22 LP mm−1@MTF(modulation transfer function) = 0.2. Besides, this flexible film enables X‐ray imaging of curved objects and stores optical information for >48 h. This work provides a paradigm for improving the RL intensity and X‐ray detection sensitivity of alkali rare‐earth fluorides by crystal defect engineering, and enriches X‐ray high resolution extended imaging applications.

Influence of composition on luminescence properties of Cd1-xZnxWO4 solid solutions

A set of single-phase Cd1-xZnxWO4 (x = 0–1) solid solutions synthesized by spontaneous crystallization technique was studied by the methods of luminescence and electron paramagnetic resonance (EPR) spectroscopy. Luminescence spectra of all studied solutions are characterised by a single emission band related to the intrinsic emission of self-trapped excitons. The dependence of luminescence spectra and thermostimulated luminescence (TSL) curves on solution composition was investigated, and the origin of TSL peaks was analysed on the basis of the EPR data. It is shown that the values of optical bandgap and activation energy of luminescence thermal quenching gradually change with solution composition. Several phenomena are observed in solid solutions predominantly at intermediate concentrations of Cd and Zn cations that can be connected with the structural disorder of the solid solutions. In particular, the deviation of lattice parameters from the Vegard's law, the redshift and broadening of the emission band, the suppression of low-temperature (T < 80 K) TSL peaks related to self-trapped holes and the broadening of high-temperature (100–200 K) TSL peaks related to structural defects. The structural disorder arises due to the non-homogeneous distribution of substitutional atoms in cation lattice sites, pronounced because of the mismatch in ionic radii of substitutional cations, which reaches 28.3 % for Cd2+ and Zn2+.

Trap engineering in LiInSi2O6:Cr,Pr by excess cristobalite silica for X-ray activated near-infrared persistent luminescence imaging in vivo

Chromium-doped persistent luminescence nanoparticles (PLNPs) have promising biomedical applications in X-ray charged near-infrared (NIR) luminous imaging. The persistent luminescence (PersL) property was usually adjusted by co-doping with other ions. Impurity phases were thought to be adverse to the PersL. In this study, a composite material, LiInSi2O6:Cr,Pr·2SiO2 (LICP-S), was synthesized with a PersL peak at 800 nm after being charged by 1 Gy X-ray while LiInSi2O6:Cr (LIC) and LiInSi2O6:Cr,Pr (LICP) possessed no or very weak PersL. Distinctively, excess metastable cristobalite silica was found essential for the much more intense PersL of LICP-S than LICP and LIC. Thermostimulated luminescence spectra studies indicated that cristobalite adjusted the Pr-related traps from deep traps to shallow ones, which facilitated the room temperature PersL. The low dose X-ray charged PersL of LICP-S was applied to demonstrate the luminous labeling of a medical silicone prosthesis that was supposed to be imbedded in body for years via X-ray activated PersL imaging in vitro and in vivo. This work not only provides a kind of PLNPs with 800 nm emission suitable for low dose X-ray activation, but also an unusual strategy for trap engineering in PersL materials by designing multi-phase composites.

Interconfigurational d-f luminescence of Pr3+ ions in praseodymium doped Li6Y(BO3)3 single crystals

Luminescence properties of undoped Li6Y(BO3)3 (LYB) crystals grown by the Bridgman method as well as undoped and praseodymium doped LYB crystals grown by the Czochralski method were studied under excitation by ultraviolet light, synchrotron radiation and electron beam in the temperature region of 5–300 K. The emission bands peaking at 4.8, 3.76 and 2.95 eV were found in undoped Czochralski-grown crystals, while the band at 3.34 eV was dominant in the Bridgman-grown crystals. These bands are presumably ascribed to excitons localized at regular and defect-perturbed lattice sites. Intense emission bands peaking at 4.75, 4.50, 4.17 and 3.98 eV were discovered in Pr doped crystals at low temperatures and related to the interconfigurational 4f15d1 → 4f2 radiative transitions in Pr3+ ions. The structure of the emission spectrum is shown to be determined by the 3H4, 3H5, 3H6, 3F2, 3F3, 3F4 terms of the Pr3+ ion. The characteristic decay time of the 4f15d1 → 4f2 emission is τ = 24 ns at low temperatures, however, it shortens to 9 ns by room temperature due to a strong thermal quenching. The study of glow curves and spectra of thermostimulated luminescence in Li6Y(BO3)3:Pr crystal irradiated by 10-keV electron beam shows that Pr3+ ions do not participate in an electron-hole recombination process.

Ultraviolet-C persistent luminescence and defect properties in Ca2Al2SiO7:Pr3+

In recent years, significant attention has been focused on the study of materials with ultraviolet (UV) persistent luminescence (PersL) due to their prospective application possibilities. Although novel UV persistent phosphors are being developed, reports on defect properties and PersL mechanisms are limited. In this study, the incorporation of Pr3+ ions in Ca2Al2SiO7 is analyzed using X-ray diffraction (XRD) and X-ray absorption techniques, whereas PersL properties are characterized by photoluminescence (PL), thermostimulated luminescence (TSL) and electron paramagnetic resonance (EPR) methods. Analysis of the Pr L3-edge X-ray absorption spectra suggests that praseodymium atoms substitute for calcium atoms. The UV-C PersL of the host results from thermally assisted recombination of charge carriers with trap depths within the 0.50–0.87 eV range. Moreover, a partial correlation of PersL and TSL with the decay of X-ray-induced paramagnetic centers was observed. This study expands the knowledge base on the structure of Ca2Al2SiO7 and establishes the optimal Pr3+ concentration for efficient UV-C PersL.

Thermostimulated luminescence analysis of oxygen vacancies in HfO[formula omitted] nanoparticles

Hafnia has already been established in CMOS technologies as a high-k metal gate material, however, recently it has also become a promising material in ferroelectric applications. In this study we have investigated intrinsic defects such as oxygen vacancies in undoped and 5at%Eu HfO2 synthesized by sol-gel, combustion, auto-ignition combustion, hydrothermal and precipitation methods. All samples were of monoclinic phase with crystallite sizes of 16–40 nm. Photoluminescence (PL), thermostimulated luminescence (TSL) both below and above room temperature as well as XRD and TEM methods were used to identify potential VO3+1, VO3+2, VO4+1 and VO4+2 defects. Activation energies were determined for the oxygen vacancies and grain boundary effects were studied. Both PL and TSL wavelength peak spectra shift to higher energies with the increase of temperature was observed.

Influence of growth process and crystal defects on sapphire brittleness

Brittleness of sapphire has been studied by four point bending and ball on three ball tests. A significantly larger flexural stress was observed for crystals grown by the Verneuil process compared to EFG (Edge-defined Film-fed Growth) crystals. Crystallographic defects were characterized by X-ray topography and it was shown that subgrain boundaries found in Verneuil crystals do not impact the fracture behavior. Larger amounts of basal dislocations in Verneuil boules appeared to account for the differences in brittleness. The dislocation densities have been related to the temperature fields experienced by the crystals during the growth processes. Characterization of point defects by thermo-stimulated luminescence revealed that they are more numerous in Verneuil crystals, especially after annealing, and that they pin dislocations, contributing to the mechanical response of the crystal.

Structure and persistent luminescence of novel Pr-doped Mg3Lu2Ge3O12 garnet

Garnet-based materials are widely investigated for applications in optics. In this research, we report the structure and spectroscopic properties of novel Mg3Lu2Ge3O12: Pr3+ garnet that exhibits orange persistent luminescence. The atomic positions of Mg3Lu2Ge3O12 were calculated using Rietveld refinement. The local structure analysis using extended X-ray absorption fine structure (EXAFS) and site-selective spectroscopy revealed that activator ions predominantly incorporate in the Lu3+ position. The persistent luminescence processes in Mg3Lu2Ge3O12: Pr3+ were analysed using photoluminescence (PL), thermostimulated luminescence (TSL), and electron paramagnetic resonance (EPR) spectroscopy methods. The comparison of PL and persistent luminescence spectra imply that electron and hole traps are filled due to the photoionization of Pr3+ ions. Two paramagnetic defects related to O- sites were detected after the excitation. TSL analysis indicates a quasi-continuous charge trap distribution ranging from 0.57 to 1.51 eV in the investigated host, enabling efficient persistent luminescence. The persistent luminescence mechanism of Mg3Lu2Ge3O12: Pr3+ is proposed.

Development of a red persistent luminescent composite: Electrospun nanofiber polymer coating prevents emission quenching by water

Sulfide persistent luminescent materials are known for their efficient luminescence, although a limitation in application of these materials is their susceptibility to hydrolysis. In this work, the electrospinning technique was used to encapsulate polycrystalline SrS:Eu2+,Sm3+ within PVDF-co-HFP nanofibers, after which thermostimulated luminescence could be observed with the naked eye following treatment with boiling water, confirming that the storage capacity of the powder was maintained after encapsulation. The composite material presented high levels of flexibility, hydrophobicity, and thermal and chemical stability. The structural characteristics of the synthesized SrS:Eu2+,Sm3+ were elucidated using X-ray diffraction (XRD), infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The morphologies of the SrS:Eu2+,Sm3+ grains and the electrospun nanofibers were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray fluorescence (XRF) mapping, and scanning transmission X-ray microscopy (STXM). Mechanical properties including elastic modulus and deformation degree were evaluated by PeakForce quantitative nanomechanical mapping (PF-QNM). The luminescent properties were investigated using photoluminescence spectroscopy (PLS), diffuse reflectance spectroscopy (DRS), and X-ray excited optical luminescence (XEOL), which showed that the photonic functionality of the material in the nanofibers was preserved, even after severe treatment with boiling water.

Basic Characteristics of Dose Distributions of Photons Beam for Radiotherapeutic Applications Using YAG:Ce Crystal Detectors.

Thermostimulated luminescence (TSL) dosimetry is a versatile tool for the assessment of dose from ionizing radiation. In this work, the Ce3+ doped Y3Al5O12 garnet (YAG:Ce) with a density ρ = 4.56 g/cm3 and effective atomic number Zeff = 35 emerged as a prospective TSL material in radiotherapy applications due to its excellent radiation stability, uniformity of structural and optical properties, high yield of TSL, and good position of main glow peak around 290-300 °C. Namely, the set of TSL detectors produced from the YAG:Ce single crystal is used for identification of the uniformity of dose and energy spectra of X-ray radiation generated by the clinical accelerator with 6 MV and 15 MV beams located in Radiotherapy Department at the Oncology Center in Bydgoszcz, Poland. We have found that the YAG:Ce crystal detects shows very promising results for registration of X-ray radiation generated by the accelerator with 6 MV beam. The next step in the research is connected with application of TSL detectors based on the crystals of much heavier garnets than YAG. It is estimated that the LuAG:Ce garnet crystals with high density ρ = 6.0 g/cm3 and Zeff = 62 can be used to evaluate the X-rays produced by the accelerator with the 15 MV beam.

Tuneable persistent luminescence of novel Mg3Y2Ge3O12 garnet

In this work novel garnet persistent luminescence phosphor Mg3Y2Ge3O12: Tb3+ (MYG: Tb3+) with bright blue to green tuneable emission is reported.MYG: Tb3+ samples with Tb3+ content ranging from 0 % to 100 % were analysed. X-ray absorption spectroscopy analysis showed that Tb3+ ions incorporate in the garnet structure by replacing Y3+ ions. Optimal dopant content was determined to achieve bright afterglow lasting more than ten hours. Tuneability of persistent luminescence was attributed to the deviations in populations of 5D4 and 5D3 emitting states of Tb3+ due to multiphonon relaxation and cross-relaxation processes.Photoluminescence, thermostimulated luminescence (TSL) and electron paramagnetic resonance (EPR) methods were used to determine the dominant persistent luminescence processes in the investigated material. The analysis of intrinsic defects in the material using EPR spectroscopy showed the presence of three distinct paramagnetic V-type centres and at least one F-type centre. The role of Tb3+ as a charge trap was discussed. MYG: Tb3+ exhibited luminescence tuneability by doping and temperature, which is promising for advanced anti-counterfeiting applications.

Luminescence of ZnO:Ga ceramics under sub-threshold electron irradiation

The luminescence of ZnO:Ga ceramics was studied at room temperature under 270 keV electrons irradiation. The near band gap and defects related luminescence intensity independence on irradiation dose up to 9.4 × 1013 e/cm2 as well as absence of thermostimulated luminescence within 300–600 K confirm that ZnO:Ga ceramics is radiation hard material for sub-threshold energy electron irradiation and therefore is prospective as scintillator for sub-threshold electrons detection. The near band gap luminescence peak position is at 393 nm under electron beam irradiation, and it is shifted to the long wave side relative to photoluminescence. The origin of the observed shift could be both – the difference of recharged donor-acceptor pairs created under photoexcitation and electron beam irradiation as well as contribution from host material self-absorption.

Thermostimulated luminescence mechanisms of UV irradiated zirconium dioxide nanotubes

A nanotubular layer of zirconium dioxide was synthesized with anodic oxidation. Curves of spectrally resolved thermostimulated luminescence were studied in the 390-550 nm range after 300 nm UV irradiation. Energetic and kinetic parameters of thermostimulated luminescence curves were estimated. The mechanism of thermally-activated processes involving intrinsic lattice defects is proposed. Keywords: Spectrally resolved thermostimulated luminescence, zirconium dioxide, nanotubes, electron and hole traps.

The structural and luminescence properties of plexcitonic structures based on Ag2S/l-Cys quantum dots and Au nanorods.

A technique of obtaining plexitonic structures based on Ag2S quantum dots passivated with l-cysteine (Ag2S/l-Cys QDs) in the presence of Au nanorods passivated with cetyltrimethylammonium bromide molecules (Au/CTAB NRs) with controlled luminescence properties has been developed. The structural and luminescence properties of Ag2S/l-Cys QDs with Au/CTAB NRs are studied. The effect of plasmonic Au/CTAB NRs on IR trap state luminescence (750 nm) is considered. It has been found that the direct interaction between the components of the plexcitonic nanostructure leads to a significant luminescence quenching of Ag2S/l-Cys QDs, with the luminescence lifetime being constant. This is the evidence for photoinduced charge transfer. The spatial separation of the components of plexcitonic nanostructures due to the introduction of a polymer – poly(diallyldimethylammonium chloride) (polyDADMAC) provides a means to change their mutual arrangement and achieve an increase in the IR trap state luminescence intensity and a decrease in the luminescence lifetime from 7.2 ns to 4.5 ns. With weak plexcitonic coupling in the nanostructures [Ag2S QD/l-Cys]/[polyDADMAC]/[Au/CTAB NRs], the possibility of increasing the quantum yield of trap state luminescence for Ag2S QDs due to the Purcell effect has been demonstrated. In the case of formation [Ag2S QD/l-Cys]/[polyDADMAC]/[Au/CTAB NRs] a transformation of shallow trap state structure was established using the thermostimulated luminescence method.

Comparison of Characteristics of Thermostimulated Luminescence of CdS Nanostructures Obtained by Green Synthesis and Chemical Method

Comparison of Characteristics of Thermostimulated Luminescence of CdS Nanostructures Obtained by Green Synthesis and Chemical Method

A digital technology for scanning the luminescent characteristics of alkali halide crystals

A digital technology for scanning the X-ray luminescence, tunnel luminescence, and thermostimulated luminescence spectra in the spectral range from 200 nm to 850 nm is experimentally demonstrated using the example of a NaCl crystal, which is part of the group of alkali halide crystals. This is done with the specified spectrum intervals and scanning speed using a high-aperture monochromator MSD-2 and a photoelectronic multiplier type H 8259 of the company “Hamamatsu”, operating in the photon counting mode, controlled by special programs SpectraScan and ThermoScan. The obtained experimental data are digitally converted for further processing of the graphical representation of the results using the OriginPro software package, which allows you to draw up graphical dependencies of the spectra and perform their mathematical processing.

Bulk and surface processes in KBr single crystals examined by thermostimulated luminescence and exo-electron emission

This article belongs to a three-part series dedicated to the simultaneous measurements of thermally stimulated exo-electron emission (TSEE), desorption (TSD) and luminescence (TSL). These works aim is to verify the ability of the applied experimental setup to characterize and analyze at the same time all the three above-mentioned stimulated processes. In agreement with the two preceding publications that deal TSD and TSEE, this article proves the consistency of the results of the individual modes of joint measurements of TSL and TSEE (as well as bulk and surface, the corresponding sources of emission, the recombination processes and their interactions). The whole experimental apparatus was tested using a well-known material, high-purity monocrystalline KBr, in the temperature range ΔT = −196 °C–430 °C (ΔT = 77 K–703 K) and in the chamber with base pressure p < 1 × 10−6 Pa to obtain a better comparison of results. Our in-house developed software for decomposing of the measured curves into the individual components and the subsequent calculation of the corresponding activation energies and frequency factors clearly confirms these results.

Re-Evaluation of Chromium Doped Alumina for Dosimetric Applications

Abstract Many medical examinations involve ionizing radiation. Although the range of available dosimeters is rather wide, their linearity and chemical stability are limited. Recently, there has been a growing interest in new, improved dosimetric materials for emerging applications in medicine and other fields, such as sterilisation of consumer goods and medical instruments, irradiation of seeds, chemical agents and others. One of the classical dosimeters is carbon-doped alumina (Al2O3:C) – a well-established and widely used material for personal and industrial dosimeter with a range of great properties, such as high sensitivity, wide linearity range and relative ease of production and handling. However, the demand for reliable dosimeters in a high-dose range is still only partially fulfilled, and alumina doped with chromium ions (Al2O3:Cr) can be a promising candidate. In this study, we explored alumina doped with chromium porous microparticles synthesized with a sol-gel method as a possible high dose dosimeter and evaluated its thermostimulated luminescence signal, dose response with two irradiation sources and measured long-time fading. It was found that although the TSL signal was quite complex (consisting of two main peaks above room temperature) and the long-term fading was significant (around 50 % in the span of 30 days), with sufficient optimisation the material could be used as a high-dose dosimeter for X-ray and beta irradiation. Wide high dose linearity range, physical and chemical characteristics, as well as low production costs and ease of synthesis make chromium (III) doped alumina a compelling candidate for applicability in various medical and industry fields.

Enhancement of persistent luminescence in Ca2SnO4: Sm3+

Reddish-orange persistent luminescent Ca2SnO4: 0.1% Sm3+ co-doped with 0–10% Gd3+ was prepared using solid state synthesis. The phase formation and morphology was analyzed using X-ray diffraction and scanning electron microscopy. Incorporation of Sm3+ and Gd3+ in Ca2SnO4 lattice was investigated using site-selective spectroscopy and electron paramagnetic resonance. In all samples reddish-orange persistent luminescence and photochromic effect was observed after excitation with UV as well as X-rays. The thermostimulated luminescence curves indicated that the introduction of Gd3+ increases the number of shallow traps of charges which enhance the intensity of persistent luminescence. In samples with high Gd3+ content (5–10%) an additional luminescence band in the near-infrared spectral region was detected. The origin of this band was discussed.