Lu2O3:Pr,Hf Storage Phosphor: Compositional and Technological Issues

Lu2O3:Pr,Hf ceramics were investigated using mainly thermoluminescence (TL) technique. Their ability to efficiently store energy acquired upon irradiation with X-rays was proven. The best TL performance was achieved for compositions containing 0.025%–0.05% of Pr and about 0.1% of Hf. Further enhancement of TL efficiency was attained by increasing the temperature of sintering of the ceramics up to 1700 °C and applying reducing atmosphere of forming gas. It was also proven that fast cooling after the sintering at 1700 °C significantly enhanced the storage phosphor performance. TL glow curve contained three components peaking around 130, 250 and 350 °C. Among them, the one at 250 °C contributed the most to the total TL

The mechanism of X-ray excited luminescence in BaHfO3\mathrm{BaHfO_{3}} doped with Eu3+\mathrm{Eu^{3+}}, Y3+\mathrm{Y^{3+}} or Eu3+\mathrm{Eu^{3+}}, La3+\mathrm{La^{3+}}

Luminescent properties ofBaHfO$_{3}$:Eu codoped with Y$^{3+}$ and La$^{3+}$ were investigated. It was found that the codopants influence the location of Eu$^{3+}$ in the host lattice. Y$^{3+}$ directs Eu$^{3+}$ into Ba$^{2+}$ and La$^{3+}$ channels Eu$^{3+}$ into Hf$^{4+}$ site. The mechanism of the process is discussed. Both, Eu'$_{Hf}$ and Eu$_{Ba}$ show photoluminescence but only the former one exhibits X-ray excited luminescence. This phenomenon is explained based on the electronic structure of BaHfO$_3$ host

Traps Formation and Characterization in Long-Term Energy Storing Lu2O3:Pr,HfLu_{2}O_{3}:Pr,Hf Luminescent Ceramics

Sintered ceramics of Lu2O3:Pr,Hf storage phosphor were prepared and their spectroscopic properties were evaluated. It was shown that during irradiation with X-rays as well as with short UV radiation, the material was able to accumulate energy, which could thereafter be recovered by thermal stimulation in the range of approximately 20–450 °C. The glow curve consisted of three bands peaking around 130, 250, and 340 °C, and each of them contained two overlapping components related to traps, with activation energies in the range of 0.8–2.1 eV. Frequency factors of the traps exceeded the Debye frequency by 3–4 orders of magnitude indicating a complex mechanism of the process. The thermoluminescence was found to follow the first-order kinetics mechanism. A 30% fading was recorded after nine months. The stored energy could also be totally recovered with optical stimulation around 400 nm. Both dopants, Hf(IV) and Pr3+, were found to be active in permanent energy trapping, forming electron (Hf) and hole (Pr) traps

On the Luminescence of HfGeO4_4:Ti4+^{4+} X-ray Phosphor and Luminescence Thermometer

The HfGeO4:Ti phosphor was investigated, focusing on its thermoluminescence properties in the range of 30−500 °C and photoluminescence in the 13–600 K. The nominal Ti content was 1%, while 0.2% concentration was proved by EDS. The thermoluminescence exposed three TL peaks at 70, 120, and 180 °C whose properties were analyzed. Emissions peaking at 430 nm under 255 nm excitation, 580 nm under 320 nm, and 790 nm under 355 nm were identified and characterized. The latter two were not reported earlier. The 790 nm emission is suggested to result from slight contamination with rutile-TiO2. Contrary to the emission intensity, which slightly increased from 13 K to about 200 K, the decay time of the 430 nm luminescence started shortening at just about 40 K. The 580 and 790 nm luminescence is thermally quenched within ∼30–400 K range. Relative thermal sensitivity of 7.67%/K at 62 K (430 nm luminescence), and 6.04%/K at 73 K (580 nm) were achieved using decay time as the thermometric parameter. The HfGeO4:0.2%Ti appeared to be a very good luminescence thermometer operating in a wide range of 30–600 K, with sensitivities higher than 0.4%/K

On site-selective optically and thermally induced processes in Lu2O3:Tb,Ta\mathrm{{Lu_2O_3}:Tb,Ta} storage phosphors

Photo- thermo- and optically stimulated luminescence properties of $\mathrm{Lu_2O_3:Tb,Ta}$ ceramics sintered at 1700 °C in air were investigated. Low temperature (10 K) excitation and emission spectra using synchrotron excitation in the range of 150–330 nm are also discussed. The effect of the dopant contents on the various luminescence effects and processes was tackled. The ceramics showed intense thermoluminescence (TL) and the glow curve consisted of two main peaks around 170 and 250 °C upon 5 °C/s heating rate. The shape of the glow curve and TL intensity depended strongly on the dopant concentrations. Above 0.1% of their contents the TL quickly lessened to disappear around 1%. This was in contrary to photoluminescence which hardly showed any quenching up to the concentration of 1%. In addition to the regular first order TL kinetics some contribution from tunneling and semi-localized transitions was proved

Flux-Aided Synthesis of Lu2O3 and Lu2O3:Eu—Single Crystal Structure, Morphology Control and Radioluminescence Efficiency

Li2SO4 or (Li2SO4 + SiO2)-mixture fluxes were used to prepare a Lu2O3:Eu powder phosphor as well as an undoped Lu2O3 utilizing commercial lutetia and europia as starting reagents. SEM images showed that the fabricated powders were non-agglomerated and the particles sizes varied from single microns to tens of micrometers depending largely on the flux composition rather than the oxide(s)-to-flux ratio. In the presence of SiO2 in the flux, certain grains grew up to 300–400 μm. The lack of agglomeration and the large sizes of crystallites allowed making single crystal structural measurements and analysis on an undoped Lu2O3 obtained by means of the flux technique. The cubic structure with a = 10.393(2) Å, and Ia space group at 298 K was determined. The most efficient radioluminescence of Lu2O3:Eu powders reached 95%–105% of the commercial Gd2O2S:Eu

Fine structure in high resolution 4f7–4f65d excitation and emission spectra of X-ray induced Eu2+ centers in LuPO4:Eu sintered ceramics

X-ray induced effects in LuPO4:Eu3+ sintered thermoluminescent material were investigated by absorption and photoluminescence measurements between 20 and 300 K. Evidence for Eu3+→Eu2+ conversion upon exposure to X-rays was obtained as narrow band blue Eu2+ photoluminescence was observed. The low temperature luminescence of Eu2+ ions in X-rayed LuPO4:Eu ceramics showed a unique fine structure with a sharp zero-phonon line at 425.8 nm and well-resolved vibronic structure. Excitation spectra of the Eu2+ luminescence revealed a rich structure in which individual 4f7→ 4f6(7FJ)5d1 zero-phonon lines accompanied by vibronic transitions were identified. A detailed analysis allowed an accurate calculation of the Eu3+-like 4 f6(7FJ) core levels in the 4 f65d1 excited configuration. The 4f6 core splitting is different from that of the 7FJ states for Eu3+ in LuPO4, providing evidence for the role of 4f6–5d interaction on the splitting of the 4f6 configuration. The unique luminescence of Eu2+ with a small Stokes shift and well-determined energies of 4f6(7FJ)5d1 excited states make LuPO4:Eu a model system for testing theoretical models which are presently developed to calculate and predict the energy level structure and Stokes shift of 4fn–4fn−15d1 transitions of lanthanides

On energy storage of Lu2O3:Tb,M (M=Hf, Ti, Nb) sintered ceramics: Glow curves, dose-response dependence, radiation hardness and self-dose effect

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.Accepted Author ManuscriptRST/Luminescence Material