Excitation mechanism of blue and infrared emission in ZnSe:Cr

ZnSe:Cr-based infrared (IR) laser operating at room temperature is of great interest shows the near-edge photoluminescence (PL) spectra of Cr-doped ZnSe observed under 337.1 nm excitation. A broad blue PL band at 427 nm is observed for lightly Cr-doped samples and the sample doped with Cr from the Bi + Cr melt. Blue PL band is excited by two-step complementary photoionization transitions of chromium ions. Free carriers photo-generated in the conduction and valence bands of ZnSe participate in the band-to-band transitions responsible for the blue emission. Free holes generated in the valence band under chromium ionization are efficiently trapped by shallow acceptor centres being active in the blue emission process. The second photon, which is absorbed by photo-generated Cr⁺ state, induces a complementary ionization transition to the conduction band. Thus, both types of free carriers are photo-generated and responsible for the blue PL.