. The donor fluorescence decay was not fit by the law t 0.5 and the quenching efficiency was characterized by the square-law dependence on the concentration and a very poor dependency on the temperature. The analysis of some models allows us to assume, that in this case the cooperative quenching of the 1 D 2 states of both type Pr 3+ optical centers can take place.

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crystals has revealed that the concentration threshold of luminescence quenching is strikingly low for nanocrystals. In this case the ordered stage in the 1 D 2 luminescence decay has been observed at anomalously low Pr concentration (0.5 at%). This effect is caused by the preferred Pr accumulation at the nanocrystal periphery that provides the relaxation of elastic tension arising due to the difference of ionic radii of Pr 3+ and Y 3+. The temporal behavior of the 1 D 2 luminescence decay in the disordered stage shows that the concentration quenching is caused by the cooperative cross-relaxation.

It is shown on the basis of studies of the optical spectra and luminescence decay of nonequivalent Pr3+ optical centers in the Y2SiO5 crystal that the occupation of the nonequivalent cation sites of the crystal lattice by the activator ions is irregular. For excitation in the region of the optical transitions H43→1D2in the temperature interval 6–80 K there is no transfer of electronic excitation energy between Pr3+ ions localized in different cation sites. The luminescence decay law of the Pr3+ optical centers is determined by the concentration of activator ions and has a complicated non-single-exponential character; the quenching of the luminescence of the Pr3+ ions is due to the formation of dimers of these ions. © 2002 American Institute of Physics.

An analysis of the absorption and luminescence spectra of a Y2SiO5:Pr3+ crystal has revealed the existence of two Pr3+ optical centers associated with the presence of impurity ions at nonequivalent cation sites. It is found that energy is transported nonradiatively between the nonequivalent Pr3+ optical centers. and a preliminary analysis of the transport mechanism is carried out.