This work presents a fresh insight into the excited charges trapping in the Lu₂O₃:Tb,M (M= Ti, Hf) ceramics and their characteristics as storage and/or persistent luminescence phosphors. The results were obtained by applying an exceedingly versatile set of experiments based on thermoluminescence and thermoluminescence excitation spectroscopy and exposed a dual-nature of these materials. In the contrary to the previous research, here we found that at least some of these materials can generate efficient persistent luminescence due to the presence of shallow traps which can be charged only upon specific irradiation conditions – by the spin-forbidden 4f→5d transition of Tb³⁺ around 360 nm and, possibly, the ⁷F₆→⁵D₃ intra-configurational transition of the activator at just slightly longer wavelengths. Besides that, changing the sample charging temperature the efficiency of filling the traps – both deep and shallow – with the 360 nm radiation varied greatly and exposed a very broad distribution of trap energies. Charging with 360 nm radiation at room temperature fills only the shallow traps giving, never reported in Lu₂O₃:Tb,Ti and Lu₂O₃:Tb,Hf, intense persistent luminescence, while at higher temperatures the deep traps are filled. At any temperature, radiation of wavelengths < 320 nm fills almost exclusively deep traps responsible for TL at high temperatures, 230 °C in Lu₂O₃:Tb,Hf and 355 °C in Lu₂O₃:Tb,Ti.

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Thermoluminescent properties and energy storage characteristics of Lu₂O₃:Tb,M (M = Hf, Ti, Nb) sintered ceramics induced by ionizing radiation are presented and discussed. Dose-response dependence, radiation hardness and fading are studied. A linearity of the former exceeding seven orders of magnitude is confirmed for Lu₂O₃:Tb,Hf and Lu₂O₃:Tb,Nb ceramics. Lu₂O₃:Tb,Hf shows the best TL performance and also its fading is the lowest reaching 15% over 7 h and shows tendency to saturate. During the same period of time the Lu₂O₃:Tb,Ti, despite having TL at higher temperatures, losses about 25% of the stored energy and the TL signal of Lu₂O₃:Tb,Nb fades by almost 40% over 7 h. First order TL kinetics is confirmed for all three compositions. A self-dose effect in Lu₂O₃:Tb,Hf due to a natural content of the radioactive isotope (2.6%) is proved to be important for long-time reading of low doses.

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Lu₂O₃:Pr,Ti storage phosphors were prepared by means of high temperature (1700 °C) sintering both in a reducing atmosphere of the N₂-H₂ mixture (3:1 by volume) and in ambient air. Their thermoluminescent (TL) properties were presented and discussed. Pr singly-doped material showed only very inefficient TL. Ti co-doping boosted the TL efficacy, and the most potent TL was observed for ceramics containing 0.05 mol% of Pr and 0.007 mol% of Ti and made in the reducing atmosphere. Samples prepared in air produced noticeably less intense TL. The glow curves of both materials consisted of one broad asymmetric band with the maximum around 357 °C for the heating rate of 4.7 °C/s. The glow peaks could be fitted with three (reduced samples) or two (air-sintered) components. The latter lacked the high-temperature part of TL compared to the former. T_max-T_stop experiments indicated that the TL is connected with continuous distribution of trap depths, which were estimated to cover the range of ~ 1.7 to 2.3 eV, and their specific values were slightly dependent on the methodology. Anomalous dependence of the TL intensity on the heating rate made the semi-localized transition the likely mechanism affecting the TL properties of Lu₂O₃:Pr,Ti ceramics. The collected data allowed to construct vacuum referred binding energy (VRBE) level scheme with Pr³⁺ and Ti^3+/4+ energy levels in the band gap of Lu₂O₃ host that could explain the TL mechanism in Lu₂O₃:Pr,Ti ceramics.

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Ceramics of Lu2O3 activated with either Tb3+ or Pr3+ and co-doped with one of the transition metal ions – Ti, Hf or Nb – were investigated for their energy storage properties. Photoluminescence, thermoluminescence (TL) and optically stimulated luminescence spectra were recorded and discussed together with thermoluminescent glow curves. The Pr3+ and Tb3+ ions constitute luminescent centers and participate in the energy storage. However, as the thermoluminescence glow curves showed, the Ti, Hf and Nb co-dopants have a significant impact on glow curve pattern, in particular on the temperature at which the maximum thermoluminescence occurred. For the Tb,Ti and Pr,Ti as well as for the Pr,Nb one main TL peak appeared around 360–370 °C. For other compositions it varied from 210 °C for Tb,Nb, through 230 °C for Tb,Hf to 250 °C for Pr,Hf. In either case additional TL components of lower intensities were observed. They spread over 50–450 °C. The TL data led to the conclusion that the co-dopant – a necessary component to induce a significant energy storage capacity in the materials – may not be directly involved in trapping the excited carriers. Instead, it may rather generate other point defects which, individually or as clusters, would do the work. Energy storage was found to be connected with an appearance of an induced excitation/absorption band spreading over around 350–500 nm and peaking near 400 nm. A prolonged stimulation into this band caused green (for Tb-series) or red (for Pr-series) optically stimulated emission. Such a stimulation allows entirely bleaching out the induced absorption. The optically stimulated luminescence for all members of the Tb-series led to luminescence from both C2 and C3i sites offered by the host lattice. All compositions of the Pr-series produced optically stimulated emissions upon 400 nm radiation only by means of the Pr3+ occupying the C2 site.@en