RECOMBINATION PROCESSES IN LINBO3 CRYSTALS

It has been shown that luminescence recombination of excited states ca n occur with the participation of shallow levels (the measurements of cathodo- and thermoluminescence on nominally pure and Mg- and Fe-doped lithium niobate crystals). These processes compete with the processes of trapping of charge carriers by deep levels, determining the photor efraction of crystals. Therefore, an enhancement or suppression of pho torefraction can be achieved by changing not only the state and the nu mber of deep levels, but also by changing shallow levels that determin e the recombination of excited carriers, It is also shown that ''non-p hotorefractive'' dopants (ME) can affect photorefraction not only by c hanging the state of ''photorefractive'' dopants (Fe), but also by inc reasing the efficiency of charge recombination. A scheme of levels tak ing into account both deep traps and shallow recombination centers is suggested for a lithium niobate crystal.