RESONANCE ENERGY TRANSFER IN $SIO_{2} - {UO_{2}}^{2+}$ ADSORPTION SYSTEM

Abstract

Low-temperature luminescence spectra of molecular ions ${UO_{2}}^{2+}$ adsorbed on disperse $SiO_{2}$ surface were investigated under selective laser excitation. It has been shown that molecular ions are very sensitive luminescent probes for investigations of active in adsorption centers (AC) on disperse silicon dioxide surface. Different AC cause many "elementary" luminescence spectra. The very great half-width of the luminescence maxima can be explained by an nommiform broadening of emission spectra that is due to the change of the water-uranyl complexes perturbation degree by AC formation. The intensity distribution functions of contribution for "elementary" spectra have been calculated. There are several resonance points for dependence of "elementary" spectra's contributions to total luminescence spectrum. It has been found experimentally the phenomenon of resonance energy transfer among various AC in their excited states. The resonance energy transfer is result the coincidence of the perturbation energy value and symmetrical and deformation vibrations' energy in exited states. The resonance parameters have bee calculated. The time of non-radiative energy relaxation among various complexes excited state has been defined. It has been shown also that the time of non-radiative energy relaxation among these AC is consistent with the time of vibrational relaxation in each concrete AC and much less that the luminescence decay time constant. Thus, emission efficiency in such adsorption systems is caused by the time constant of luminescence decay in lowermost excited state and independents on peculiarities of energy relaxation processes from higher excited states. Values of the bond energies lend support of the validity of the water-uranyl model of AC and the electrostatic consideration used.