Growth and ultraviolet optical properties of KGd1–xREx(WO4)2 single crystals

Abstract

The suitable conditions for growth of KGd(WO4)2 (KGW) and KGd1–xREx(WO4)2— RE = Nd, Er, Yb, Ho, Tm, Pr—by the top-seeded-solution-growth method, using K2W2O7 as solvent, are discussed. The relation between crystal size, mean growth rate, distribution coefficient of the substituting element, and the presence of macrodefects is analyzed. The optical absorption corresponding to the band-gap transition of KGW has been found to be temperature dependent; the absorption threshold energy changes from 34405 cm−1 at 300 K to 35330 cm−1 at 7 K. Narrow pre-edge absorption bands at about 32000 and 32600 cm−1 have been ascribed to Gd3+ intraconfigurational transitions. The photoluminescence of most RE3+ ions has been observed under ultraviolet (UV) excitation close to the absorption threshold of KGW. This suggests the contribution of charge transfer bands. In Pr-doped samples the presence of a minor concentration of Pr4+ could also contribute in this region. The irradiation with UV light does not introduce any significant coloration of our samples.