Photoluminescent properties of semiconducting Tl ₆I ₄Se

The photoluminescence (PL) from the wide bandgap semiconductor Tl ₆I ₄Se, a promising candidate material for gamma ray detection, was studied at low temperature. The Tl ₆I ₄Se single crystal was grown by the Bridgman method. For undoped material, we observed a single broad peak at 1.61 eV with a full width at half maximum of 112 meV at 20 K, which is attributed to donoracceptor 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.