X-ray absorption study of rare earth ions in Sr2MgSi2O7:Eu2+,R3+ persistent luminescence materials

The valence of the europium dopant and selected rare earth co-dopants (Ce3+, Dy3+, and Yb3+) in the Sr2MgSi2O7:Eu2+,R3+ persistent luminescence materials were studied by room temperature XANES measurements. The results indicated the co-existence of both divalent and trivalent europium in all the studied materials. The relative amount of Eu3+ was observed to increase upon increasing exposure to X-rays, as expected by the persistent luminescence mechanism. This suggests a simultaneous filling of oxygen vacancies initially created by the reducing preparation conditions. For the Dy and Yb co-dopants, only trivalent species were observed. On the other hand, traces of tetravalent cerium were present in the Eu,Ce co-doped materials. (c) 2009 Elsevier B.V. All rights reserved

Understanding Persistent Luminescence: Rare-Earth- and Eu2+\mathrm{Eu^{2+}}-doped Sr2MgSi2O7\mathrm{Sr_{2}MgSi_2O_7}

Similar to many other Eu2+,RE3+-co-doped persistent luminescence materials, for Sr2MgSi2O7:Eu2+,RE3+ the initial intensity and duration of persistent luminescence was also found to depend critically on the rare-earth (RE) co-doping. An enhancement of 1 - 2 orders of magnitude in these properties could be obtained by Dy3+ co-doping whereas total quenching of persistent luminescence resulted from the use of Sm3+ and Yb3+. To solve this drastic disparity, the effects of the individual RE3+ ions were studied with thermoluminescence (TL) spectroscopy to derive information about the formation of traps storing the excitation energy. The charge compensation defects were concluded to be the origin of the complex TL glow curve structure. The tuning of the band gap of the Sr2MgSi2O7 host and especially the position of the bottom of the conduction band due to the Eu2+,RE3+ co-doping was measured with the synchrotron radiation vacuum UV (VUV) excitation spectra of the Eu2+ dopant. The model based on the evolution of the band gap energy with RE3+ co-doping was found to explain the intensity and duration of the persistent luminescence.</jats:p

Wavelength-sensitive energy storage in Sr3MgSi2O8:Eu2+,Dy3+Sr_3MgSi_2O_8:Eu^{2+},Dy^{3+}

Optical energy storage materials can store energy when exposed to radiation and subsequently release it as light after thermal or optical stimulation. Such materials are thus employed in, e.g., detectors, dosimetry, self-lit signs, and imaging. In, e.g., dosimetry, the response of the material is correlated with the absorbed energy, but no distinction of different radiation energies can be achieved. In this work, $Sr_3MgSi_2O_8:Eu^{2+},Dy^{3+}$ was studied with thermoluminescence (TL) initiated by irradiating the material with photon energies between 2.6 (480) and 5.4 eV (230 nm). The TL glow curves revealed that the material has two main traps. Both the overall TL intensity and the TL intensity ratio between the two traps strongly depend on the photon energy of the irradiation. A mechanism of energy storage and charge carrier release in this material was constructed from the results obtained

Persistent luminescence fading in Sr2MgSi2O7:Eu2+,R3+ materials: a thermoluminescence study

The fading of persistent luminescence in Sr2MgSi2O7:Eu2+,R3+ (R: Y, La-Nd, Sm-Lu) was studied combining thermoluminescence (TL) and room temperature (persistent) luminescence measurements to gain more information on the mechanism of persistent luminescence. The TL glow curves showed the main trap signal at ca. 80 degrees C, corresponding to 0.6 eV as the trap depth, with every R co-dopant. The TL measurements carried out with different irradiation times revealed the general order nature of the TL bands. The results obtained from the deconvolutions of the glow curves allowed the prediction of the fading of persistent luminescence with good accuracy, though only when using the Becquerel decay law. (C) 2012 Optical Society of AmericaTurku University FoundationTurku University FoundationJenny and Antti Wihuri Foundation (Finland)Jenny and Antti Wihuri Foundation (Finland)Academy of Finland [117057/2000, 123976/2006, 134459/2009, 137333/2010]Academy of FinlandCAPES (Brazil)CAPES (Brazil

DFT and synchrotron radiation study of Eu2+ doped BaAl2O4

The structural distortions resulting from the size mismatch between the Eu2+ luminescent centre and the host Ba2+ cation as well as the electronic structure of BaAl2O4:Eu2+(,Dy3+) were studied using density functional theory (DFT) calculations and synchrotron radiation (SR) luminescence spectroscopy. The modified interionic distances as well as differences in the total energies indicate that Eu2+ prefers the smaller of the two possible Ba sites in the BaAl2O4 host. The calculated Eu2+ 4f(7) and 4f(6)5d(1) ground level energies confirm that the excited electrons can reach easily the conduction band for subsequent trapping. In addition to the green luminescence, a weak blue emission band was observed in BaAl2O4:Eu2+,Dy3+ probably due to the creation of a new Ba2+ site due to the effect of water exposure on the host. (C) 2012 Optical Society of AmericaTurku University FoundationJenny and Antti Wihuri Foundation (Finland)Academy of Finland [123976/2006, 134459/2009, 137333/2010, 112816/2006/JH, 116142/2006/JH, 123976/2007/TL]Academy of Sciences of the Czech RepublicCzech research project [AVOZ10100521]European Community [RII3-CT-2004-506008]CNPqNanobiotec-Brasil RH-INAMIinctINAMIFAPESPCoimbra GroupCAPES (Brazil