Comparison study of energy bands and Wannier-Mott excitons in mixed Zn(P

Excitonic absorption, reflection and photoluminescence spectra of mixed Zn(P1-xAsx)2 crystals over the full range of x ($0 \leq x \leq 1$) and Zn1-xAsxCdxP2 crystals at $0 \leq x \leq 0.05$ have been studied at low temperatures (1.8 K). The decrease of the energy gap in Zn(P1-xAsx)2 at the increase of x occurs slightly sublinearly. The rydbergs of excitonic series in this crystals decrease as well, and the dependences Ry(x) for all series are strongly superlinear at small x. In Zn1-xCdxP2 crystals the energy gap and rydbergs decrease at the increase of x (at $0 \leq x \leq 0.05$) as well. The dependences of Eg and Ry on x are considerably stronger in Zn(P1-xAsx)2 than in Zn1-xCdxP2. At the increase of x the half-width of excitonic absorption lines increases monotonically in both type crystals that is evidence of the increasing role of fluctuations of crystal potential