Selective pair luminescence in the 1.4-eV band of CdTe:In

We investigated the photoluminescence (PL) of CdTe doped with indium using above- and below-bandgap excitation at temperatures of 4.5−20 K. We recorded and measured the selectively excited PL arising from the recombination of donor-acceptor (D–A) pairs with the A-center acceptor in the spectral region of the 1.4-eV PL band for different excitation photon energies, $ℏωEXC$⁠. Sharp, strong PL lines that shifted with $ℏωEXC$ over the total contour of the D–A pair band represented the selective pair luminescence (SPL). The energy difference of ∼125 meV between the excited- and ground-state of the charged D–A pair is very close to the 6-longitudinal-optical phonon energy in CdTe. This multiplicity favors the relaxation of an excited hole to the ground state of an acceptor, and increases the probability of recombination in the D–A pair. The SPL line quenches with temperature, characteristically with energy of 6–14 meV for D–A pairs with different D-A distances. The temperature shift of the 1.4-eV band supposedly is caused by the redistribution of occupied- and empty-shallow donors neighboring the A-center.