Creation of F centres and multiplication of electronic excitations in Na6Al6Si6O24(NaBr)(2x) optical ceramics under VUV irradiation

The reflection spectra, the excitation spectra of various emissions (2.4-4. 5 eV) and the creation spectra of F centres have been measured in Na6Al6Si6 O24(NaBr)(2x) optical sodalite ceramics (x = 0.94 and x = 0.81) using VUV r adiation of 6-35 eV. An analysis of the spectra allowed us to separate seve ral groups of electronic excitations: the photons of 6.7-8.3 eV excite or i onize Br- centres in the beta -cages, 8.5-32 eV photons generate electronic excitations of the aluminosilicate carcass, while 33 eV photons excite Na ions up to the 2p(5)3s state. The creation mechanism of F centres, connect ed with the trapping of conduction electrons by pre-irradiation bromine vac ancies and localization of holes at Br- centres in beta -cages. has been re vealed in sodalites at 80 K. The efficiency of F centre creation triples in the multiplication region of electronic excitations of the aluminosilicate carcass (20-30 eV) in a sample with x = 0.94. Using methods of thermoactiv ation spectroscopy, the creation of thermally stable F centres (up to 480 K ) has been detected in sodalites irradiated by x-rays or 27 eV photons. How ever. such F centres cannot be created by 7.6-11 eV photons, i.e. when ther e is no multiplication of excitations and an exciting photon forms only one electronic excitation.