Low-temperature luminescence and thermally stimulated luminescence of BeO: Mg single crystals

Luminescence and thermally stimulated luminescence (TL) of BeO: Mg crystals are studied at T = 6–380 K. The TL glow curves and the spectra of luminescence (1.2–6.5 eV), luminescence excitation, and reflection (3.7–20 eV) are obtained. It is found that the introduction of an isovalent magnesium impurity into BeO leads to the appearance of three new broad luminescence bands at 6.2–6.3, 4.3–4.4, and 1.9–2.6 eV. The first two are attributed to the radiative annihilation of a relaxed near-impurity (Mg) exciton, the excited state of which is formed as a result of energy transfer by free excitons. The impurity VUV and UV bands are compared with those for the intrinsic luminescence of BeO caused by the radiative annihilation of self-trapped excitons (STE) of two kinds: the band at 6.2–6.3 eV of BeO: Mg is compared with the band at 6.7 eV (STE_1) of BeO, and the band at 4.3–4.4 eV is compared with the band at 4.9 eV (STE^2) of BeO. In the visible region, the luminescence spectrum is due to a superposition of intracenter transitions in an impurity complex including a magnesium ion. The manifestation of X-ray-induced luminescence bands at T = 6 K in BeO: Mg indicates their excitation during band-to-band transitions and in recombination processes. The energy characteristics of the impurity states in BeO: Mg are determined; the effect of the isovalent impurity on the fluctuation rearrangement of the BeO: Mg structure in the thermal transformation region of STE_1 → STE_2 is revealed.

Thermally stimulated luminescence of undoped and Ce3+-doped Gd2SiO5 and (Lu,Gd)2SiO5 single crystals

TSL kinetic parameters and dosimetric properties of TlAlF4 crystal grown by Bridgman technique

ABSTRACTWe report on non-contact and non-destructive spatially resolved characterization of traps and luminescence centers in vanadium-free semi-insulating 6H-SiC. Two optical techniques were employed: photoluminescence (PL) mapping and thermally stimulated luminescence (TSL) imaging on SiC wafers. PL and TSL topography reveal inhomogeneity at the periphery regions of the wafers. Low-temperature PL spectra show broad bands with the maxima at 1.75eV and 1.2eV, including a sharp zero-phonon line at 1.344eV. The TSL glow curves at T>80K show different peaks in the visible and infrared bands. The luminescence spectrum of the 105K TSL peak replicates 1.75eV band, while the 120K peak corresponds to the 1.2eV band. Additionally, the high temperature TSL peak at 210K shows an excellent match with 1.344eV zero phonon line. The trap energies of different peaks are calculated. We discuss a model of complex defects composed of closely spaced electron (hole) trap and UD3 defect.

Ce-doping effect on dosimetric properties of mullite single crystals synthesized by the floating zone method

Afterglow is an important phenomenon in luminescent materials and can be desired (e.g., persistent phosphors) or undesired (e.g., scintillators). Understanding and predicting afterglow is often based on analysis of thermally stimulated luminescence (TSL) glow curves, assuming the presence of one or more discrete trap states. Here we present a new approach for the description of the time-dependent afterglow from TSL glow curves using a model with a distribution of trap depths. The method is based on the deconvolution of the energy dependent density of occupied traps derived from TSL glow curves using Tikhonov regularization. To test the validity of this new approach, the procedure is applied to experimental TSL and afterglow data for Lu1Gd2Ga3Al2O12:Ce ceramics codoped with 40 ppm of Yb3+ or Eu3+ traps. The experimentally measured afterglow curves are compared with simulations based on models with and without the continuous trap depth distribution. The analysis clearly demonstrates the presence of a distribution of trap depths and shows that the new approach gives a more accurate description of the experimentally observed afterglow. The new method will be especially useful in understanding and reducing undesired afterglow in scintillators.

Electronic traps in mixed Si 1− xGe xO 2 films

Synthesis of Tb-doped SiO2 glasses by spark plasma sintering method and evaluation of photoluminsecence and thermally stimulated luminescence properties

Thermally stimulated luminescence (TSL) glow curves induced by × and beta irradiations have been performed on SiO2 films, thermally grown in “dry” and “wet” atmospheres. The distribution of the thermoluminescent defects in the oxide thickness has been studied, as well as the effects on the TSL glow curves of annealing treatment, of boron concentration in the silicon substrate, and of alkali ions doping. It follows from these experiments that it is highly probable that the traps and luminescent centers responsible for the TSL emission are of intrinsic character. Furthermore, comparisons with TSL glow curves and the closely related phenomenology of crystalline quartz and amorphous silica let us suggest that the dominant luminescent center emitting at 3.1 eV in silica and quartz is probably the same in all the forms of SiO2, including films.

The research results of the luminescence spectra and thermally stimulated luminescence (TSL) in β-Ga 2 O 3 and β-Ga 1,9 In 0,1 O 3 single crystals doped with chromium ions, grown by the optical melting zone method, have been presented. The Cr 3+ impurity concentration was 0.05%. Luminescence was excited by light with a wavelength of 440 nm from the region of the broad absorption band 4 A 2 → 4 T 1 of Cr 3+ ions. Two sharp R-lines ( 2 E → 4 A 2 transitions) are dominated in the luminescence spectrum of investigated samples at the temperature of liquid nitrogen. A number of weak narrow lines associated with the phonon-induced sidebands of the R -lines are observed in the wavelength range of 700-740 nm. At room temperature, a broad luminescence band extending from 650 to 900 nm is dominated and corresponds to electron-vibrational 4 T 2 → 4 A 2 transitions in chromium ions. The R -lines are also observed on the background of this broad luminescence band in the luminescence spectrum of chromium impurity in gallium oxide at room temperature. The luminescence of chromium impurity in solid solutions is concentrated only in a broad luminescence band with a maximum near 775 nm ( 4 T 2 → 4 A 2 transitions). Doping of β-Ga 2 O 3 with a chromium impurity leads to the appearance of a thermoluminescence maximum at 285 K, which corresponds to traps with an energy depth of 0.59 eV. In the crystals of the solid solution, there is a shift of the TSL maximum to the range of low temperatures up to 225 K and an increase in its half-width. The fractional thermal-glow technique was used to analyze the TSL complex maximum at 225 K. It was established that this maximum consists of at least 4 elementary maxima, which are caused by the release of electrons from traps with activation energies in the ranges of 0.4-0.42 and 0.48-0.495 eV. The method of the initial increase in the intensity of the TSL glow was used to calculate the activation energy. Keywords : β-Ga 2 O 3 , solid solutions, thermally stimulated luminescence, activation energy.

An insight into indium effect on the crystal structure and thermoluminescence of LiMgPO4: Combined experiment and ab initio calculations

The low-temperature thermally stimulated luminescence (TSL) in both porous silicon (PS) layers on Si substrate and PS powder has been found in the 4.2–300 K temperature range. The dependence of the TSL effect on the wavelength and temperature of an excitation was studied in detail. The shape of TSL glow curves displays the quasicontinuous spectrum of the electron states in the gap of PS and the activation energy is subject to the linear law of E[eV]=0.0029T−0.14 at T>70 K. For the homogeneous PS powder, the TSL glow curves weakly depend on an excitation wavelength. For the PS layer on Si substrate the maximum of the TSL glow curve shifts to the higher temperature both at the excitation by the short wavelength light and by the supplementary exposition to IR illumination. Such behavior is stipulated by the gradient of the PS energy band gap with the depth and, consequently, by the reconstruction of electron states in the band gap. It is shown that the TSL is conditioned by the photoluminescence (PhL) in PS bulk, and the spectral distribution of the TSL signal at 100–120 K is close to its PhL spectrum excited at 546 nm.

In this study, we grew the Dy-doped Mg2SiO4 single crystals by the floating zone method to investigate the photoluminescence (PL) and thermally stimulated luminescence (TSL) properties. All the Dy-doped Mg2SiO4 showed the emission peaks at 480, 580, and 670 nm in PL and TSL spectra, and these peak wavelengths were typical for the 4f–4f transitions of Dy3+ ions. In the TSL glow curves, all the samples had the glow peaks at 50 °C, 200 °C, 280 °C, and 380 °C. The TSL dose response function of the 1% Dy-doped Mg2SiO4 single crystal showed a good linearity across 1–10000 mGy.

Effect of W and Mo co-doping on the photo- and thermally stimulated luminescence and defects creation processes in Gd3(Ga,Al)5O12:Ce crystals

Low-temperature luminescence and thermoluminescence from BeO:Zn single crystals