Intracenter radiative transitions at tantalum impurity centers in cadmium telluride

Luminescence spectra of Ta impurity centers in CdTe are studied for the first time. It is found that, as the 3$d$ (Ta) electron system of centers is considered instead of the 3$d$ (V) system, a substantial change in the characteristics of impurity-related emission is observed. Electron transitions are identified in accordance with the Tanabe–Sugano diagrams of crystal-field theory. It is established that radiative transitions occur within isolated Ta$^{3+}_{\mathrm{Cd}}$ centers, between levels with different spins. Temperature broadening of the zero-phonon line of tantalum is induced by the interaction of $d$ electrons of the center with TA phonons of the crystal lattice. However, in interpreting the data on the temperature shift of the line, it is essential to take into account the hybridization of local impurity states and band states. Temperature quenching of the luminescence signal occurs with activation energies of 60 and 160 meV. The radiative lifetime of centers in CdTe:Ta is 1.5 $\mu$s.