Electron paramagnetic resonance and photoluminescence studies of chromium in SrS

Isotropic features with hyperfine structures in electron paramagnetic resonance spectra of SrS powder phosphors, which reflect the abundance of the natural Cr isotopes, are attributed to the isolated Cr impurity. The isotropy, which is typical for a 4A2 ground state of a 3d3 ion in an octahedral crystal field, and the g value of 1.9795 verify that Cr is observed in its charged donor state Cr3+. The observation of a broad photoluminescence band with a maximum at 900 nm, which can be attributed to an internal Cr3+ transition, supports the identification of the impurity as Cr3+.