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A number of Lu2O3-based materials were reported to present efficient capability of trapping excited charge carriers in metastable excited states formed either by specific dopants or naturally occurring defects. Over the years, abundant experimental data have been collected, which were taken as a solid ground to treat the problem using computational chemistry. Density functional theory (DFT) calculations with an advanced meta generalized gradient approximation (mGGA) functional were used to analyze electron trapping in cubic Lu2O3 doped with Hf. Individual ions of dopant and nearest-neighbor dopant ion pairs were considered. The effects of interstitial anions such as O2- and Cl- were analyzed. In most of the analyzed cases the additional electron charge is localized at the dopant site. However, in many of the studied cases, the dopant/defect states overlap with the conduction band and cannot correspond to electron trapping. The Hf3+ ion in the Lu site of C3i local symmetry (Hf Lu-C3i ) corresponds to a moderate trap depth of 0.8-0.9 eV. Several composite defects corresponding to deeper (1.1-1.4 eV) traps also exist. Unambiguous deep traps (1.5-1.8 eV) correspond to systems with Hf dopant in the cationic void, accompanied by two interstitial oxygen atoms. The results thus indicate that basic 'Hf-substitutes-Lu' doping is unlikely to correspond to the deep traps observed experimentally in Lu2O3:Tb,Hf andLu2O3:Pr,Hf and more complex defects must be involved. [ABSTRACT FROM AUTHOR]

Effects of defect introduction on electronic structure of cubic Ia-3 lutetium oxide (Lu 2 O 3 ) were characterized by means of density-functional theory calculations using augmented plane wave method with local orbitals (APW+LO) approach. Perdew-Wang 92 local density approximation (LDA) and Räsänen, Pittalis, and Proetto meta-generalized gradient approximation (meta-GGA) density functionals were used. It was found that interstitial oxygen (introduced into the oxygen void available in the structure) and lutetium vacancies result in defect states located about 0.1–0.8 eV above valence band, which can act as hole traps. Oxygen vacancy can act as efficient electron trap, with depth about 1.25 eV. Interstitial lutetium in either C 3i cation void or in oxygen void results in states located about 0.2–1 eV below conduction band, which can act as electron traps. Both interstitial Lu and Lu vacancies create multiple traps of different depths, which might contribute to experimentally observed trap distributions in Lu 2 O 3 . [ABSTRACT FROM AUTHOR]

For the first time thermoluminescence of Lu 2 O 3 :Tb,Ta ceramics sintered at 1700 °C in different atmospheres – air, forming gas and vacuum – were investigated. Exposure of the materials into the 254 nm radiation of a mercury lamp led to the Tb 3+ green persistent luminescence of noticeable intensity. Thermoluminescence glow curves revealed two strong thermoluminescence peaks located around 170 °C and 250 °C, with the former being by a factor of ~2–2.5 more intense compared to the latter. T max -T stop thermoluminescence experiments revealed that each of these bands is composed of numerous individual, strongly overlapping components of similar characteristics, known as continuous traps distribution. The highest thermoluminescence was observed from the material sintered in vacuum. Those sintered in air or forming gas showed the storage capabilities by about 15–25% lower, though shapes of their glow curves were very similar. A scheme of carriers trapping was proposed with the hole immobilized at Tb 3+ site and the electron being trapped in the vicinity Ta(V) impurity due to its strong positive net charge in the Lu site. [ABSTRACT FROM AUTHOR]

Electronic structure of Ta-doped cubic (bixbyite-type) lutetium oxide was analyzed using augmented plane wave with local orbitals density functional theory (DFT) calculations with meta-generalized gradient approximation (meta -GGA, mGGA) Räsänen, Pittalis and Proetto functional. Two doping sites, three oxidation states of the dopant and optional interstitial oxygen (O i) were considered. The calculations indicate that introduction of the dopant results in energy levels below conduction band, with strong contribution of Ta 5 d orbitals. The position of the levels depends strongly on the oxidation state of the dopant. Depending on the composition, two distinct electron traps with depths of 1.5–1.2 eV and 0.9–0.2 eV were revealed. Introduction of O i at proximity of the Ta dopant results in partial overlap of the Ta-related defect states with conduction band, which makes the traps very shallow, deteriorating the electron trapping properties. In some cases, shallow hole traps can also be attributed to the O i. The calculated traps structure is in good accord with the experimental data. Image 1 • Ta-doped cubic (bixbyite-type) lutetium oxide was analyzed using FP-LAPW/mGGA DFT calculations. • Two doping sites, three oxidation states of the dopant and optional interstitial oxygen were considered. • Two distinct electron traps (related to Ta 5 d orbitals) with depths of 1.5–1.2 eV and 0.9–0.2 eV were revealed. • Introduction of interstitial oxygen at proximity of the Ta dopant deteriorates the electron trapping properties. • The calculated traps structure is in good accord with experimental data. [ABSTRACT FROM AUTHOR]

Oxyorthosilicates have long history in luminescent applications e.g. as phosphors, scintillators and in emerging technologies like luminescence thermometry. In this study we report detailed research on the thermoluminescent (TL) properties of Y 2 (Ge x ,Si 1-x)O 5 :Pr. Despite regular TL measurements, T max -T stop , initial rise analysis, fading, decay of persistent luminescence, and dose effect are presented and analyzed. The possibility to deliberately manage the electron trap depths adjusting the Ge/Si ratio is explored. Glow curve of each composition consists of two main TL peaks. In the (Ge,Si) solid continuous distribution of trap energies is observed. Strong thermoluminescence is observed from all compositions after charging with X-ray radiation. Efficiency of charging traps with UV-C photons (fitting the 4f→5d 1 transition energy) lowers systematically as the Si content increases. A growing coupling of the excited 5d 1 level of Pr3+ and the host conduction band with the increase of Ge content is responsible for this effect. A scheme of the TL-related processes is presented using the vacuum referred binding energy (VRBE) approach for all the Y 2 (Ge x ,Si 1-x)O 5 :Pr phosphors. Image 1 • Effect of bandgap engineering in Y 2 (Ge x ,Si 1-x)O 5 :Pr phosphors on intrinsic traps parameters is presented. • Thermoluminescence dependence on energy of the charging radiation is examined. • Dependence of trap depths distribution on the host composition is disclosed. [ABSTRACT FROM AUTHOR]

Depending on the dose of ionizing radiation, ScPO 4 :0.1%Eu3+ sintered ceramic presents significantly different thermoluminescent properties. Despite a thermoluminescent peak around 90 °C which appears upon small doses (up to tens of mGy) it also shows strong thermoluminescence at 240 °C but only after exposure to higher doses. In both cases, the thermoluminescence is generated by Eu3+ ions, which also serve as electron traps. Recognition of the relevant hole traps responsible for the thermoluminescent peaks needs more comprehensive research using such tools as advanced EPR spectroscopy at different temperatures. At room temperature, the thermoluminescence peak at 240 °C is very resistant to fading hardly showing any loss of intensity within 24 h. The peak at 90 °C fades continuously at ambient conditions and after 24 h its intensity drops to about 10% of its original strength. Hence, this component is responsible for the hours-lasting persistent luminescence of the ScPO 4 :0.1%Eu3+ ceramic. • Drastic dose-dependence of energy storage of ScPO4:Eu ceramics is presented. • Low doses produce one thermoluminescence peak, high doses gives two separate peaks. • AT high doses the high-temperature peak prevails the low-temperature one. [ABSTRACT FROM AUTHOR]

ScPO 4 :0.1%Eu3+ sintered materials were found to generate orange-red persistent emission following exposure to X-rays. A set of thermoluminescence techniques and isothermal decay measurements were used to study the mechanisms of the carriers' trapping and detrapping processes. The two main TL peaks at around 90 °C (363 K) and 160 °C (433 K) were found to result from so-called continuous distribution of trap depths. Room temperature fading proved that the persistent luminescence was connected with the strong TL peak at ∼90 °C (363 K). The persistent emission kinetics was characterized by a linear dependence of I −1(t). This was consistent with the continuous distribution of trap energies observed in the material. The main persistent emission components were located around 590, 620, and 720 nm. The most significant contribution was from the first and the third of them, resulting from the 5D 0 →7F 1 and 5D 0 →7F 4 transitions, respectively. • Orange-red persistent luminescence of ScPO 4 :Eu ceramics is presented for the first time. • Mechanism of carriers trapping is presented and hole and electron trapping centers are Eu3+ and O-ligand, respectively. • Comparison to similar ceramics of LuPO 4 :Eu is presented and discussed. [ABSTRACT FROM AUTHOR]