  Low-temperature (1.8 K) excitonic absorption, reflection and
photoluminescence spectra of mixed $Zn(P_{1 - x}As_{x})_{2}$ crystals were
studied at $x = $0.01, 0.02, 0.03 and 0.05. Energy gap and rydbergs of
excitonic B, C and A-series decrease monotonically at the increase of $x$.
Spectral half-widths of absorption $n = 1$ lines of B and A-series increase
monotonically at the increase of $x$ due to fluctuations of crystal potential.
Emission lines of excitonic molecules were observed in photoluminescence
spectra of $Zn(P_{1 - x}As_{x})_{2}$ crystals. Binding energy of molecule
increases at the increase of $x$ that is due to the decrease of the
electron-hole mass ratio.
