Thermal quenching of Ce3+ luminescence in the cuspidine-type oxide nitride compounds Y4Si2-xAlxO7+xN2-x

Y3.98Ce0.02AlxO7+xN2-x system with x equal to 0, 0.2, 0.4, 0.6, 0.8, 1.0 and 1.2 doped with Ce3+ were synthesized by gas pressure sintering (GPS) system. It was found that Ce3+ at different sites in Y3.98Ce0.02AlxO7+xN2-x system creates several types of emission centers which have the same emission energy with maximum near 510 nm but differ in quenching temperature. When part of Si-N is replaced by Al-O in Y3.98Ce0.02Si2O7N2, the position of the Ce3+ emission maximum slightly shifts to higher energy and the emission intensity as well as decay time of luminescence strongly decreases. Both thermal ionization to conduction band and thermal excitation to CTE (Cerium Trapped Exciton) are responsible for non-radiative quenching and low efficiency of the system. It is shown that the luminescence quenching by the CTE state activates at lower temperature because of the much lower activation energy. The detailed analysis of the temperature dependence of the luminescence decay shown that the various Ce3+ sites differ mainly by location of the Ce3+ localized states in the bandgap, whereas difference between the first excited states 5d(1) and the ground state of Ce3+ is approximately the same.