Figure 3. Experimental verification of the Ca₂ZnN₂ and CaZn₂N₂ phases.

Schematics of experimental set-ups and X-ray diffraction profiles for (a) a polycrystalline sample with a starting composition of Ca:Zn:N=2:1:2 aiming at the formation of the Ca₂ZnN₂ phase, which was encapsulated in a sealed steel tube and annealed at 680 °C for 40 h, and (b) a polycrystalline sample treated at 1200 °C and 5.0 GPa for 1 h with a starting composition of 1:2:2 corresponding to CaZn₂N₂. Also shown are simulated profiles that were obtained on the basis of the theoretically predicted crystal structure of CaZn₂N₂ and the reported crystal structures of Ca₂ZnN₂ and Zn. The broad peaks around 2θ=20° originate from sample capsules used in the measurements. (c) Absorption spectra of Ca₂ZnN₂ and CaZn₂N₂ derived from diffuse reflectance spectra at 300 K and the Kubelka–Munk relation (α: absorption coefficient; S: scattering factor; and hν: photon energy). (d) Photoluminescence (PL) from CaZn₂N₂: PL spectra at 10, 100, 200 and 300 K (left of panel), the temperature dependence of the PL peak position (middle of panel) and a photograph of red PL at 10 K (right of panel).