Tuning 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 the 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, 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 inducible factors. The variation of cell parameters and component contents confirm the substitution of La3+ site with six coordinates by the inducible ions. After excluding the possibility of defective luminescence by thermoluminesence spectra, activated Eu2+ in the six coordinates is proved to be the reason for the new luminescence centers of Eu2+ using Eu3+ ion as the lattice probe, in which the decisive role of inducible factors is elaborately discussed. Results open an effective avenue for spectral adjustment in multi-site phosphors via artificially inducing potential luminescence centers.