Resonance energy transfer in SiO{sub 2} - UO{sub 2}{sup 2+} adsorption system

Low-temperature luminescence spectra of molecular ions UO{sub 2}{sup 2+} adsorbed on a disperse SiO{sub 2} surface were investigated under selective laser excitation. It has been shown that molecular ions are very sensitive luminescent probes for investigations of for investigations of active absorption centers (AC) on disperse silicon dioxide surfaces. Different AC cause many {open_quotes}elementary{close_quotes} luminescence spectra. The very great half-width of the luminescence maxima, can be explained by an nonuniform 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 contributions for {open_quotes}elementary{close_quotes} spectra have been calculated. There are several resonance points for dependence of {open_quotes}elementary{close_quotes} spectra`s contributions to a total luminescence spectrum. It has been found experimentally that the phenomenon of resonance energy transfer among various AC in their excited states. The resonance energy transfer is the result of the coincidence of the perturbation energy value and symmetrical and deformation vibration energy in exited states. The resonance parameters have been 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 timemore » 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 the lowermost excited state and is independent of peculiarities of energy relaxation processes from higher excited states. Values of the bond energies lend support to the validity of the water-uranyl model of AC and the electrostatic consideration used.« less