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

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, us ing K2W2O7 as solvent, are discussed. The relation between crystal size, me an growth rate, distribution coefficient of the substituting element, and t he presence of macrodefects is analyzed. The optical absorption correspondi ng tc the band-gap transition of KGW has been found to be temperature depen dent; 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 3 2600 cm(-1) have been ascribed to Gd3+ intraconfigurational transitions. Th e 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 irr adiation with UV light does not introduce any significant coloration of our samples.