Optical absorption spectra in thin films of M2Ag1-xCuxI3 (M=K,Rb,Cs) solid solutions.

A study is made of the excitonic absorption spectra of solid solutions of the system (KI)2–(1-x)AgI–xCuI. On the basis of the dependence of the parameters of the excitonic bands on the concentration x, it is established that solid solutions of the type K2Ag1-xCuxI3 are formed in the range 0≤x≤0.2. Substitution of Ag atoms by Cu atoms in the AgI42- tetrahedra, which form chains in the orthorhombic crystal K2AgI3, promotes the formation of quasi-1D exciton bands and spectra of the persistence type, according to the Onodera–Toyozawa classification, with a splitting off of the impurity band from the exciton band. Comparison with the results of studies of the excitonic spectra in solid solutions Rb2Ag1-xCuxI3 and Cs2Ag1-xCuxI3 attests to the appearance of the Rashba effect at small x and to qualitative agreement with the Onodera–Toyozawa theory. [ABSTRACT FROM AUTHOR]