Influence of high pressure on Sr2SiO4:Eu2+ luminescence

Eu2+ doped Sr2SiO4 phosphors were synthesized by solid state synthesis technique. The purity and crystal structure of the materials was studied with the X-ray powder diffraction. Depending on the synthesis method the materials contain one (alpha') or two (alpha' + beta) crystal phases. Luminescence properties were studied ill UV-Vis range at ambient and high hydrostatic pressure. Two broad emission bands in the yellow-orange and blue-green region were attributed to the 9-fold coordinated and 10-fold coordinated Eu2+, respectively. We found that increasing pressure causes a red shift of the yellow-orange emission. This is typical pressure dependence related to 4f(6)5d(1) -> 4f(7) transition in Eu2+ observed also in other materials. In the case of blue-green band, when pressure increases from ambient to 50 kbar, the emission band shifts strongly to higher energy, and for pressure higher than 50 kbar does not depend on pressure. This effect was considered in framework of crystal field model. We presumed that electrostatic field in a 10-fold coordinated site is a superposition of crystal field of four ligands that belong to tetrahedral coordination and six ligands belonging to octahedral coordination. We discussed untypical pressure dependence of the blue-green emission band as a result of pressure influence on the lower excited state in Eu2+, i.e. 4f(6)5d(1)(e) at octahedral and 4f(6)5d(1)(t) at tetrahedral coordination. (C) 2012 Elsevier B.V. All rights reserved.