The growth and optical assessment of Cr3+-doped RX(BO3)4 crystals with R = Y, Gd; X = Al, Sc

This paper reports the high temperature top-seeded solution growth (TSSG) of Cr3+-doped mixed borate crystals having the general formula RX3(BO3)4, with R3+ = Y3+ or Gd3+ and X3+ = Al3+ or Sc3+. Both YAl3(BO3)4 (YAB) and GdAl3(BO3)4 (GAB) have been grown from a mixed K2Mo3O10B2O3 flux, whereas YSc3(BO3)4 (YSB) and GdSc3(BO3)4 (GSB) are grown from K2Mo3O10Li2B4O7 mixtures. Typical crystals ranging in volume from 60 mm3 to 14 cm3 have been grown, with Cr3+ concentrations of order 0.2–5.0 at%. Measurements of the optical absorption and luminescence spectra show that in YAl3(BO3)4 and GdAl3(BO3)4 the Cr3+ ions occupy strong crystal field sites whereas in YSc3(BO3)4 and GdSc3(BO3)4 these ions occupy weak field sites. The significance of this observation is that the Cr3+ ions in weak field sites emit via the broadband 4T2 → 4A2 transitions, with obvious potential as tunable laser gain media.