The growth and optical assessment of Cr 3+-doped RX(BO 3) 4 crystals with R = Y, Gd; X = Al, Sc

Abstract

This paper reports the high temperature top-seeded solution growth (TSSG) of Cr 3+-doped mixed borate crystals having the general formula RX 3(BO 3) 4, with R 3+ = Y 3+ or Gd 3+ and X 3+ = Al 3+ or Sc 3+. Both YAl 3(BO 3) 4 (YAB) and GdAl 3(BO 3) 4 (GAB) have been grown from a mixed K 2Mo 3O 10B 2O 3 flux, whereas YSc 3(BO 3) 4 (YSB) and GdSc 3(BO 3) 4 (GSB) are grown from K 2Mo 3O 10Li 2B 4O 7 mixtures. Typical crystals ranging in volume from 60 mm 3 to 14 cm 3 have been grown, with Cr 3+ concentrations of order 0.2–5.0 at%. Measurements of the optical absorption and luminescence spectra show that in YAl 3(BO 3) 4 and GdAl 3(BO 3) 4 the Cr 3+ ions occupy strong crystal field sites whereas in YSc 3(BO 3) 4 and GdSc 3(BO 3) 4 these ions occupy weak field sites. The significance of this observation is that the Cr 3+ ions in weak field sites emit via the broadband 4T 2 → 4A 2 transitions, with obvious potential as tunable laser gain media.