Spectral and polarization characteristics of luminescence of ${\mathrm{Ge}}^{2+\mathrm{-}}$${\mathit{v}}_{\mathit{c}}^{\mathrm{-}}$ centers in KCl:Ge, KBr:Ge, and KI:Ge crystals have been studied in the temperature range 1.7–400 K. Several bands have been found in the emission spectrum of ${\mathrm{Ge}}^{2+\mathrm{-}}$${\mathit{v}}_{\mathit{c}}^{\mathrm{-}}$ centers. Four emission bands originate from the Jahn-Teller tetragonal (T) minima of singlet and triplet relaxed excited states (RES), all split due to the existence of a cation vacancy (${\mathit{v}}_{\mathit{c}}^{\mathrm{-}}$) near the ${\mathrm{Ge}}^{2+}$ ion. Besides that, one or two red emission bands as well as a band situated between the singlet and triplet emission have also been observed in all the crystals investigated. Temperature dependences of intensities and polarization degrees of these emission bands have been studied, and the experimental manifestations of complicated relaxation and thermally stimulated processes in the excited states of ${\mathrm{Ge}}^{2+\mathrm{-}}$${\mathit{v}}_{\mathit{c}}^{\mathrm{-}}$ centers as well as cation vacancy reorientations around the ${\mathrm{Ge}}^{2+}$ ion have been detected. Decay kinetics of the triplet emission of KCl:Ge and KCl${:}^{73}$Ge crystals have been studied at temperatures down to 0.35 K, and the parameters of the triplet RES have been determined. A considerable influence of the hyperfine, spin-orbit, and vibronic interactions and of the cation vacancy associated with the ${\mathrm{Ge}}^{2+}$ ion on the luminescence characteristics as well as on the parameters of the triplet RES of ${\mathrm{Ge}}^{2+\mathrm{-}}$${\mathit{v}}_{\mathit{c}}^{\mathrm{-}}$ centers has been found. The possibility of an off-center displacement of an excited ${\mathrm{Ge}}^{2+}$ ion from the crystal-lattice site is discussed.

• Received 7 March 1994

DOI:https://doi.org/10.1103/PhysRevB.50.3553