Host lattice dependence of the Bi3+ luminescence in orthoborates LnBO3 (with Ln = Sc, Y, La, Gd, or Lu)

The luminescence properties of several Bi3+-activated lanthanide borates (LnBO3) are reported. For the calcite-structured borates (ScBO3Bi3+ and the high-temperature modification of LuBO3Bi3+), the Stokes shift is small. In the luminescence spectra vibrational structure is observed. For the compounds with YBO3 structure (low-temperature modification of LuBO3Bi3+ and YBO3Bi3+) two luminescent centers are observed. Energy transfer occurs from one type of center to the other. Finally, for LaBO3Bi3+ two centers are also observed. One is ascribed to isolated Bi3+ ions and the other to Bi3+ pairs. The Stokes shift of the Bi3+ luminescence varies from 0.22 eV for ScBO3Bi3+ to 1.16 eV for LaBO3Bi3+. This is discussed in terms of the increasing amount of space available to the Bi3+ ion in the host lattice.