For the first time, the synthesis, luminescent and structural properties of stable perovskite-type (Cs1−xRbx)4PbBr6 (R = Cs, Rb) nanocrystals are shown. In the absence of rubidium, Cs4PbBr6 and CsPbBr3 perovskite crystals precipitate in the ZnO–Na2O–B2O3–GeO2 glass matrix. With ascending rubidium content, the precipitation of (Cs,Rb)4PbBr6 nanocrystals is replaced by the Rb4PbBr6 nanocrystals nucleation. Nucleated nanocrystals exhibit an intense green luminescence. With an increase of the rubidium content, the luminescence maximum shifts to the blue region, the luminescence quantum yield increases from 28 to 51%, and the average decay time increases from 2 to 8 ns. Several assumptions have been made about the nature of the green luminescence of perovskite-like Cs4PbBr6 and (Cs,Rb)4PbBr6 crystals in glasses. It is concluded that the most probable cause is the impurity inclusions of CsPbBr3 and (Cs,Rb)PbBr3 crystals.
