TL/OSL Properties of Green Emitting LiMgPO4:Tb3+, B (LMPTB) Phosphor for Radiation Dosimetry

Study of Photoluminescence and Thermoluminescence Properties of Tb3+ Doped Green Emitting YPO4 Nanophosphors

YPO4 nanophosphors doped with different concentrations of Tb3+ were synthesized using conventional co-precipitation method. The crystalline as well structural features were studied by using powder X-ray diffraction (PXRD) as well as Transmission electron microscope (TEM) images, which revealed highly crystalline nature of the prepared samples having particle sizes of around 40 nm. EDAX spectrum also shows the elemental composition of the synthesized nanoparticles which contain Y, P, O, Tb3+as expected. Prepared samples showed emission peaks at 491, 545, 588 and 624 nm under UV excitation having excitation wavelengths of 223 and 320 nm. The Commission International de I'Eclairage (CIE)study shows the chromaticity co-ordinates for the 600oC annealed samples to be x = 0.239, y = 0.4 which corresponds to cool greenish light suggesting the potential applications of the prepared nanophosphor in white light emitting diodes converted from green phosphors, optical display setups and PDP applications. Thermoluminescence (TL) study was carried out after exposing the samples 5at.wt% Tb3+ doped YPO4 to gamma radiations. Kinetic parameters were calculated using Deconvolution method.

Uniformity of Thermoluminescence and Optically Stimulated Luminescence Signals Over the Length of Doped LiMgPO4 Crystal Rods Grown by Micro-Pulling-Down Method

The purpose of this work was to systematically assess the distribution of thermoluminescence (TL) and optically stimulated luminescence (OSL) properties along the length of crystals grown by the micro-pulling-down method, in relation to the microstructure and distribution of activators. We analyzed lithium magnesium phosphate (LiMgPO₄; LMP) crystals doped with terbium (Tb; 0.8 mol%) or with a combination of thulium (Tm; 0.8 mol% or 1.2 mol%) and boron (B; 10 mol%). Crystals of several centimeters in length and 3 mm in diameter were cut into 20-40 slices, depending on length. For each sample, TL glow curves and OSL decay curves were examined. Optical microscopy and scanning electron microscopy were used to assess the microstructure and elemental composition of several selected samples. Two-dimensional TL readouts were performed to identify the areas with higher and lower signal emission. Our study showed that there may be significant differences not only in LMP sensitivity along the crystal's axis but also on the surface of the slice. The distribution of activators varies depending on the type of crystals and strongly affects luminescence properties.

Thermoluminescence Enhancement of LiMgPO4 Crystal Host by Tb3+ and Tm3+ Trivalent Rare-Earth Ions Co-doping

We investigated the influence of terbium and thulium trivalent rare-earth (RE) ions co-doping on the luminescent properties enhancement of LiMgPO₄ (LMP) crystal host. The studied crystals were grown from the melt by micro-pulling-down (MPD) technique. Luminescent properties of the obtained crystals were investigated by thermoluminescence (TL) method. The most favorable properties and the highest luminescence enhancement were measured for Tb and Tm double doped crystals. A similar luminescence level can be also obtained for Tm, B co-doped samples. In this case, however, the low-temperature TL components have a significant contribution. The measured luminescent spectra showed a typical emission of Tb³⁺ and Tm³⁺ ions of an opposite trapping nature, namely the holes and electron-trapping sites, respectively. The most prominent transitions of ⁵D₄ → ⁷F₃ (550 nm for Tb³⁺) and ¹D₂ → ³F₄ (450 nm for Tm³⁺) were observed. It was also found that Tb³⁺ and Tm³⁺ emissions show temperature dependence in the case of double doped LMP crystal sample, which was not visible in the case of the samples doped with a single RE dopant. At a low temperature range (up to around 290 °C) Tm³⁺ emission was dominant. At higher temperatures, the electrons occupying Tm³⁺ sites started to be released giving rise to emissions from Tb-related recombination centers, and emissions from Tm³⁺ centers simultaneously decreased. At the highest temperatures, emission took place from Tb³⁺ recombination centers, but only from deeper ⁵D₄ level-related traps which had not been emptied at a lower temperature range.