Rare Earth Cathodoluminescence in InBO[sub 3] and Related Orthoborates

The cathodoluminescence from Eu3+ and Tb3+ in the orthoborates of In, Sc, Y, La, Gd, and Lu is examined. The host is shown to be particularly effective for both activators. Observed spectral details of the luminescence are related to effects of crystal symmetry on electronic transitions.