Radiative and non-radiative processes ofAg− centres doped in NaCl single crystals

Abstract

Luminescence properties including decay kinetics have been investigated forAg− centres doped in NaCl single crystals in the temperature range from 7 to 250 K. When theC absorption band peaking at 4.5 eV is photo-excited at low temperature, theA′ and C′ luminescence bands are observed at 2.85 and 4.12 eV, respectively. As the temperature increases, theA′ luminescence grows, with compensation for the decrease of the luminescence intensity of theC′ band, reflecting a thermally activated non-radiative process from the1T1u to3T1u states. With increasing temperature above 130 K, theA′ luminescence intensity also decreases. Since the decay time of theA′ luminescence is almostconstant at 10 µs above 80 K,the decrease of the A′ luminescence intensity is not attributed to a non-radiative process from the3T1u state but arises from the quenching of the non-radiative relaxation from the1T1u to3T1u states. The temperature dependence of the luminescence intensities of theA′ and C′ bands is discussed on the basis of a simple configuration coordinate model, which consists of the1T1u,3T1u and 1A1g adiabatic potential energy surfaces intersecting at each other.