Photoluminescent properties of semiconducting Tl6I4Se

The photoluminescence (PL) from the wide bandgap semiconductor Tl6I4Se, a promising candidate material for gamma ray detection, was studied at low temperature. The Tl6I4Se single crystal was grown by the Bridgman method. For undoped material, we observed a single broad peak at similar to 1.61 eV with a full width at half maximum of 112 meV at 20 K, which is attributed to donor-acceptor pair (DAP) recombination involving shallow donors and deep acceptors. From the thermal quenching of the integrated PL peak intensity, thermal activation energy of the donor level of 52 meV was obtained. At high excitation intensities a blue-shift of peak emission energy in DAP recombination was observed. From the PL measurements, the ionization energies of the donor and acceptor levels were estimated at 52 and 290 meV, respectively.