ИСТИНА

Ag- doped bulk oxyfluoride glasses have been prepared by conventional melt-quenching method. The photoluminescence excitation and emission spectra of the glass cover wide range from 300 to 500 nm and from 400 to 900 nm, respectively, corresponding to the typical spectra of Ag nanoclusters with size less than 1.2 nm. It has been argued that Ag nanoclusters are Ag42+ tetramers dispersed in fluorite type lattice. This conclusion is based on the results of Transmission Electron Microscopy, Electron Spin Resonance Measurements and Density Functional Theory Computation of excitation spectra of the Ag doped glasses. The pico-, nano- and microsecond photoluminescence kinetics of Ag nanoclusters has been detected. We have applied CASSCF/CASPT2/RASSI Quantum Chemistry methods to compute photoluminescence life-times of respective Ag nanoclusters dispersed within fluorite type lattice. Likewise, we have computed the configuration-coordinate energy level diagram of the Ag nanoclusters by the CASPT2 method. This diagram was found to be in agreement with the diagram previously computed by Density Functional Theory. Further, we have proposed the balance equations for modelling temperature and wavelength dependence of photoluminescence life-times. These equations describe the populations of the excited singlet and triplet states of the Ag nanoclusters taking into account inter-system crossing between the singlet and triplet states. The picosecond photoluminescence kinetics has been explained by Plasmon Dicke Effect as the calculated normal oscillator strengths of the Ag nanoclusters cannot account for such fast kinetics of luminescence. This confirmed by the concentration dependence of the intensity of picosecond component.