Novel laser gain media based on Cr3+-doped mixed borates RX3(BO3)4

Abstract

This letter discusses the optical properties of Cr3+ ions in mixed borate crystals with the formula RX3(BO3)4, where R3+=Y3+ or Gd3+ and X3+=Al3+ or Sc3+. Measurements of the optical absorption spectra have been used to estimate the crystal field strength Dq and the Racah parameters B and C. These quantities confirm that in YAl3(BO3)4(YAB) and GdAl3(BO3)4(GAB)Cr3+ ions occupy strong crystal field sites 2E)<E(4T2)], whereas in YSc3(BO3)4(YSB) and GdSc3(BO3)4(GSB) the Cr3+ ions occupy weak field sites 4T2)<E(2E)]. The consequence is that the fluorescence spectrum of Cr3+:YAB and GAB reveals the sharp R lines at low temperature and R lines plus broadband at 300 K. Both Cr3+:YSB and GSB emit into the broadband 4T2→4A2 transition at all temperatures. The potential of these materials as laser gain media is discussed.