Preparation of Zinc Diphosphides and the Low-Temperature Luminescence and Absorption of the Tetragonal Polymorph

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Abstract
The preparation of single crystals of black monoclinic and red tetragonal ZnP2 from the elements is described. The crystals contain 50 to 100 ppm Si as an impurity. The melting point of monoclinic ZnP2 is 992±1°C and of tetragonal ZnP2 is 985±1°C. Interplanar spacings are presented for both the red and black polymorphs of ZnP2. Two bands have been observed in the near‐bandgap luminescence of tetragonal ZnP2 at low temperatures. Both bands exhibit sharp lines, respectively, near 2.144 and 2.020 eV, due to no‐phonon decay of bound excitons, and contain much fine structure due to associated phonon‐assisted transitions. These spectra are identical with luminescence bands reported by Akopyan et al., but are attributed to recombinations in the ternary compound semiconductor ZnSiP2. Preliminary measurements of the indirect‐type absorption‐edge spectrum at low temperatures indicate that the energy gap of tetragonal ZnP2 is close to 2.220 eV at 4.2°K and ∼2.14 eV at 300°K.