Luminescence spectroscopy of Ln-doped Bi-containing phosphates and molybdates

• PL excitation of K3Bi5(PO4)6 and K2Bi(PO4)(MoO4) is related to Bi3+ ions.
• Energy transfer from Bi3+ to Eu3+ exists in K3Bi5(PO4)6:Eu and K2Bi(PO4)(MoO4):Eu.
• PL excitation spectra of K2Eu(PO4)(MoO4) are formed by O – Eu CT transitions.

The photoluminescence (PL) emission and excitation spectra of undoped and doped with rare-earth (RE = Eu, Tb) ions K3Bi5(PO4)6 and K2Bi(PO4)(MoO4) crystals are studied in 3.7–14 eV region of the excitation photon energies at T = 8 and 300 K. The mechanisms of the host-related and RE-related luminescence in 3.7–7 eV region of the excitation photon energies are revealed in comparative analysis of the PL spectra of studied compounds. It is assumed that the excitation mechanisms of host luminescence of K3Bi5(PO4)6 and K2Bi(PO4) (MoO4) crystals below 4.8 eV are related to Bi3+ ions in oxygen surrounding. An efficient energy transfer from the Bi3+-related luminescence centers to the emitting RE centers exists in crystals with low concentration of the RE dopants (1%). The PL excitation spectra of K3Bi5(PO4)6 crystals with high concentration of Eu dopants are formed by O – Eu CT transitions.