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

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

On the mechanism of persistent up-conversion luminescence in the ZrO2:Yb3+,Er3+ nanomaterials

The up-converting ZrO2:Yb3+,E3+ nanomaterials were prepared with the combustion and sal-gel methods. The structure of the materials was cubic except for the minor monoclinic and tetragonal impurities associated with the use of the sal-gel method. The XANES results revealed only the trivalent form for both the Yb and Er dopants. The distance distributions calculated from EXAFS confirm that Er3+ and Yb3+ occupy the Zr-IV site in the structure. The nanomaterials show red (650-700 nm) and very weak green (520-560 nm) up-conversion luminescence due to the F-4(9/2) -> I-4(15/2) and (H-2(11/2),S-4(3/2)) -> I-4(15/2) transitions of Er3+, respectively. The nanomaterials obtained with the combustion synthesis yield the most intense luminescence though showing significant afterglow, as well. The thermoluminescence measurements revealed the existence of traps with depths between 0.68 and 1.03 eV well matching to room temperature persistent emission. Finally, the mechanism for the persistent up-conversion luminescence was introduced based on the experimental results and discussed. (C) 2014 Elsevier B.V. All rights reserved

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