Tetrahedral substitution to induce tunable luminescent properties in apatite structural solid-solution phosphors Ca9La(PO4)5[(Si,Ge)O4]F2:Ce3+

A series of solid solution phosphors Ca9La(PO4)5[(Si1-xGex)O4]F2:Ce3+ with apatite structure in the P63/m space group have been prepared. The novel solid solution phosphors show continuously controlled violet-blue emission. It is found that both substantial spectra broadening (45 → 100 nm) and red-shift (404 → 422 nm) can be realized with the continuous introduction of [GeO4]4- into the crystal lattice which has been simulated by a crystal-field model. The above results indicate that the tetrahedral substitution is interesting to induce spectral tuning properties based on the chemical composition control of the iso-structural solid solutions.