Three-dimensional Thermoluminescence Spectra Research Articles

Near-Infrared Emission Material with Superlong Afterglow Performance and Its Multifunctional Applications.

A new near-infrared (NIR) emission material, BaSi1.5Ge2.5O9:Cr3+, with outstanding long afterglow properties is designed and synthesized successfully. Its structure, photoluminescence, and long afterglow emission features are studied in detail. Cr3+ occupies six-coordinated Ba2+ and Ge4+ sites in this system, which can emit characteristic broadband NIR light in the range of 700-1200 nm, and it has a long afterglow emission of more than 10 h. We calculated the band gap of the host at about 4.1 eV, the energy level distribution after Cr3+ doping, and the distribution of oxygen vacancies through density functional theory simulation, which theoretically proved the characteristic transition of Cr3+ and that the oxygen vacancies are crucial to form the defect energy levels. This is corroborated with the reflectance spectra, three-dimensional thermoluminescence spectra, and electron spin resonance (ESR) spectra. The oxygen-deficient environment favors the formation of oxygen vacancy defects and prevents the oxidation of Cr3+ to Cr6+, which are the key points for the luminescence and afterglow properties. A mechanistic model of defect formation and electron trapping and transport processes is successfully established. Finally, its multifunctional applications in information anticounterfeiting encryption, biological tissue penetration, and internal nondestructive testing and imaging are demonstrated.

Insights into blue-light activated red-emitting persistent luminescence from Pr3+-doped phosphors.

In recent years, a series of persistent luminescence materials excitable by blue light have been developed and widely used in many fields such as optical information storage, AC-LEDs, anti-counterfeiting and bio-imaging. However, it is still a long-standing challenge to develop a superior red-emitting persistent phosphor that can be efficiently excited by blue light. In this work, a novel blue-light excited red-emitting persistent phosphor CaCd2Ga2Ge3O12:Pr3+ was successfully synthesized by using a solid-state method, showing excellent luminescence properties. Moreover, the phase purity, crystal structure, photoluminescence spectra, afterglow emission spectra, and three-dimensional thermoluminescence spectrum were successfully investigated. Under 294 nm excitation, photoluminescence spectra show a single orange emission and a series of peaks centered at 492, 537, 568, 614 and 664 nm, which correspond to the 3P0 → 3H4, 3P0 → 3H5, 3P2 → 3H6, 1D2 → 3H4, and 3P0 → 3F2 transitions of Pr3+, respectively. Interestingly, after blue light excitation, the afterglow luminescence exhibits red long emission, which is attributed to the 1D2 → 3H4 transition of Pr3+. Through thermoluminescence spectra and three-dimensional thermoluminescence spectra, we analyze the reasons for the different colors of photoluminescence and afterglow luminescence. The results imply that there are two types of traps, and the depth of shallow traps and deep traps is calculated to be 0.684 and 0.776 eV, respectively. It is worth noting that the photoluminescence is attributed to the 4f2 → 4f5d and f → f transitions of Pr3+, and the afterglow luminescence is ascribed to a tunneling-related process and the transition of electrons from the valence band to the conduction band. The obtained red-emitting persistent phosphors provide a promising pathway toward AC-LEDs, multi-cycle bio-imaging and other fields.

UV or blue light excited red persistent perovskite phosphor with millisecond lifetime for use in AC-LEDs.

Energy storage phosphors with millisecond period afterglow that compensate for the diming time of alternating current light-emitting diodes (AC-LEDs) have promising application. To obtain a persistent luminescence (PersL) white colour in AC-LEDs, we focussed on a red afterglow with short period phosphorescence. Ca4 Ti3 O10 forms a type of perovskite-related Ruddlesden-Popper phase structure. Doping Pr3+ ions into Ca4 Ti3 O10 , an ideal red PersL was obtained. X-ray diffraction and element analysis demonstrated that our target samples were crystallized well. Steady-state and afterglow luminescence properties were investigated in detail. Notably, the PersL intensity was dependent on various excitation wavelengths. By measuring three-dimensional thermoluminescence spectra, we found that the trap depths showed a continuous distribution and that the shallowest trap contributed to the millisecond afterglow. Two PersL mechanism models were used to elucidate the electron charging and de-trapping processes under UV or blue light activation.

Three-dimensional thermoluminescence spectra of different origin quartz from Altay Orogenic belt, Xinjiang, China

Abstract Three-dimensional thermoluminescence spectra are measured for different types of geological origin quartz from the Altay orogenic belt, northern Xinjiang, China. The results show striking differences which appear to be characteristic of their geological origin. Granitic quartz is dominated by emission bands at 420–430 nm, 550–560 nm, at a temperature of 170 °C. Pegmatite quartz is characterized by an intense 480 nm emission band at 170 °C. Volcanic quartz has exclusive UV (340–360 nm) and violet (410–430 nm) emission bands. Hydrothermal quartz exhibits very different TL spectral characteristics because of different hydrothermal activity and mineralization. Only one TL peaks at 485 nm/170 °C was observed in sedimentary quartz. An intense 730 nm emission band observed at 170 °C considered generally to be characteristics of feldspar was observed in quartz from granite and hydrothermal Au-bearing quartz. This TL peak is probably related to the centre of [FeO 4 ] 0 on an Si site. All samples show an intense 990–1000 nm emission band at 330 °C. Identical types of quartz formed in different regions or different geological and tectonic settings can also exhibit striking differences in TL spectra.

Thermoluminescence emission spectra for the LiF:Mg,Cu,Na,Si thermoluminescent materials with various concentrations of the dopants (3-D measurement)

The thermoluminescence (TL) emission spectra from LiF TL materials, called KLT-300 (LiF:Mg,Cu,Na,Si) with various dopant concentrations are measured and analysed. These KLT-300 materials were developed by the Korea Atomic Energy Research Institute (KAERI) to achieve an enhancement of the thermal stability in TL readings. Six types of samples are prepared with different dopant concentrations in the following ranges; Mg (0-0.20 mol%), Cu (0-0.05 mol%), Na and Si (0-0.9 mol%). The spectra measurements are carried out for the six types of samples using a TL emission spectra measurement device. The spectra measurement device consists of a monochromator, photomultiplier tube and temperature control unit to thermally stimulate the samples. The measured data shows the light emission during heating of the sample as a function of temperature and wavelength (three-dimensional TL spectra). The spectra were analysed using a method of deconvolution based on gaussian curve. The wavelength of a main peak of the emission spectra changes depending on the existence of the Cu dopant, while intensity of the spectra rapidly changes with the Cu dopant concentrations. The 385 nm emission is mainly observed in all the spectra from the samples with the Cu dopant, but in those from the samples without the Cu dopant a very weak 401 nm emission is mainly observed. However, any change in the wavelength at a main peak of the TL emission spectra from the sample materials with Na and Si dopants is not observed but that in the intensity at a peak of the spectra is observed.

Analysis of the glow curves obtained from LiF:Mg,Cu,Na,Si TL material using the general order kinetics model.

Three-dimensional thermoluminescence (TL) spectra based on temperature, wavelength and intensity for newly developed LiF:Mg,Cu,Na,Si TL material at the Korea Atomic Energy Research Institute (KAERI) were measured and analysed. The glow curves were obtained by integration of luminescence intensity over all wavelengths at each temperature, and various trapping parameters related to the traps were determined by analysing these curves. A computerised glow curve deconvolution (CGCD) method which was based on the general order kinetics (GOK) model was used for the glow curve analysis. The glow curves of LiF:Mg,Cu,Na,Si TL material were deconvoluted to six isolated glow curves which have peak temperatures at 333, 374, 426, 466, 483 and 516 K. The main glow peak of peak temperature at 466 K had activation energy of 2.06 eV and a kinetic order of 1.05. This TL material was also found to have three recombination centres, 1.80 eV, 2.88 eV and 3.27 eV by analysis of the TL spectra.

Low temperature three-dimensional thermoluminescence spectra of undoped YVO4 single crystals grown by different techniques

Three dimensional (3D) thermoluminescence (TL) spectra of two yttrium orthovanadate (YVO4) single crystals grown from YVO4 melt by the Czochralski (CZ) technique and one additional YVO4 crystal pulled from lithium-metavanadate (LiVO3) flux by the top seeded solution growth (TSSG) method were investigated after x-ray irradiation. The TL spectra were recorded in the 200–800 nm wavelength and 20–300 K temperature ranges before and after annealing of the crystals in an oxygen atmosphere. In spite of the different growth conditions the measured 3D TL spectra of the CZ samples show similar TL characteristics. The main TL emission appears around 450 nm, and between 200 and 250 K. Further weak emissions were also detected at 570, 600, 650, and 710 nm wavelengths, which might be attributed to unwanted impurities. The TL spectrum of the TSSG crystal markedly differs from that of the CZ crystals. On one hand the major TL appears at lower temperatures whereas on the other hand the emission spectrum exhibits a broader band around 500 nm, while the weak bands between 500 and 700 nm could not be detected. Based on these observations the different defect structures in YVO4 crystals are discussed in the article emphasizing that 3D TL measurement is a useful practical tool for the characterization and identification of YVO4 crystals grown by different methods.

Three-dimensional spectral studies of the bleaching of the thermoluminescence of feldspars

Abstract Alkali feldspars, either extracted or as a component of an undifferentiated mixture, are important in thermoluminescence and optical dating. The present work describes measurements of three-dimensional thermoluminescence spectra, in which emitted light intensity is displayed as a function of both temperature and photon energy (or wavelength), for feldspars of a range of composition. In consideration of the increased role of TL/OSL in dating sediments, a particular emphasis has been an assessment of the way in which bleaching by visible and ultra-violet light affects the spectrum. Generally speaking, prolonged bleaching is necessary to remove TL from feldspars but most high-sodium feldspars in the study have a readily bleached component in the ultra-violet emission. We have not found spectral evidence for any other readily bleached peak at high glow-curve temperatures similar to the 325°C peak found in quartz. For some samples, bleaching results in increases of emission in the temperature region of interest for TL dating, and these increases appear across the emission spectrum.