The luminescent kinetic parameters of the CsPbCl 3 nanocrystals dispersed in matrices of solid solutions Rb 1−x Cs x Cl (x = 0.05 ÷ 0.2) were studied under pulse synchrotron radiation excitation. Formation of CsPbCl 3 nanocrystals is confirmed by manifestation of the quantum size effect, which is displayed by a short-wave shift of the exciton luminescence maximum and an essential shortening of the luminescence decay time for of CsPbCl 3 nanocrystals as compared to that for an excitonic luminescence of a bulk single crystal CsPbCl 3 . For the first time, using the atomic force microscopy method, the lead-containing nanocrystals embedded in a matrix of the Rb 0.95 Cs 0.05 Cl solid solution have been directly observed.