Tuning the luminescence of Ca9La(PO4)7:Eu2+via artificially inducing potential luminescence centers†
Generally, Eu2+ doped multi-site phosphors have more effective luminescent centers (m) than lattice sites (M), and the luminescence spectra would be greatly enriched if m is infinitely close or even equal to M. Herein, a series of Eu2+ doped Ca9La1−xM1.5x(PO4)7 (M = Mg, Ca, Sr, or Ba) phosphors with adjusted output color were reported for the first time, in which new luminescence centers were successfully monitored using bivalent alkaline earth metal ions as inducing factors. The variation of cell parameters and component contents confirms the substitution of La3+ sites with six coordination by the inducing ions. After excluding the possibility of defective luminescence by thermoluminescence spectra, Eu3+ ions are used as lattice probes to prove that Eu2+ activated in six coordinates is the cause of new emission center, in which the decisive role of the inducing factors is elaborately discussed. The results open an effective avenue for spectral adjustment in multi-site phosphors via artificially inducing potential luminescence centers.