Аннотация:Different versions of quantum cutting mechanisms in Yb doped Scheelite-like molybdate and tungstate single crystals were studied, with participation of various schemes of donoracceptor interaction (various kinds of donor centres: self-trapped excitons at molybdate/tungstate complexes; high-lying excited states of Yb3+ ion; Yb2+ ion; traps based on cation and oxygen vacancies; accidental impurities.). All the versions were rejected.