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.