A1 Refereed original research article in a scientific journal

Magneto-optical studies of valence instability in europium and terbium phosphors




AuthorsLucas C.V. Rodrigues, Jorma Hölsä, Hermi F. Brito, Miroslav Maryško, Jivaldo R. Matos, Petriina Paturi, Rodrigo V. Rodrigues, Mika Lastusaari

PublisherELSEVIER SCIENCE BV

Publication year2016

JournalJournal of Luminescence

Journal name in sourceJOURNAL OF LUMINESCENCE

Journal acronymJ LUMIN

Volume170

First page 701

Last page706

Number of pages6

ISSN0022-2313

DOIhttps://doi.org/10.1016/j.jlumin.2015.08.018(external)


Abstract

The impurities and dopants' inappropriate valences may deteriorate the performance of luminescent materials, cause waste of the precious rare earth (R) material and thus incur financial losses. The usual methods to detect the valence of rare earths; XPS, Mossbauer and XANES spectroscopies, are not sensitive enough for low concentrations and the EPR methods are not very suitable for powders. In this work, the comparison between the theoretical and experimental temperature-dependent paramagnetic susceptibilities was used to obtain quantitatively the concentrations of the impurity valence in Eu2O2S and Tb2O2SO4, both containing nominally only R3+. Minute (ppm level) Eu2+ impurities could be analyzed because of the huge difference in the paramagnetic susceptibility between Eu2+ and Eu3+ at low temperatures. However, temperatures below 50K are then needed whilst the Tb(IV)impurity in a Tb3+ matrix can be observed already at higher temperatures. The latter method based on comparing the slopes of the Tb3+/Tb-IV paramagnetic susceptibility vs temperature curves for the Tb3+/Tb-IV couple is less sensitive than for the Eu2+/Eu3+ one. Finally, the host independent temperature evolution of the paramagnetic susceptibility was calculated for Gd3+ (or Eu2+ or Tblv) to yield a simple analytical expression to be used universally. (C) 2015 Elsevier B.V. All rights reserved.




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