The optical absorption edge of p-type Tl(1-x)GaPrxSe2 and TlGaSe2

p-TlGaSe2 and Tl(1-x), GaPrxSe2 single crystals were grown by the modified Bridgman-Stockbarger method. The absorption measurements were carried out i n p-TlGaS2 and Tl(1-x)GaPrxSe2 samples in temperature range 10-320 K with a step of 10 K. The phonon energies calculated for p-TlGaSe2, p-Tl0.999GaPr0 .001Se2 and p-Tl0.995GaPr0.005Se2 are 34.0 meV, 30.0 meV and 35.0 meV, resp ectively. At 300 K, the direct band gaps of p-TlGaSe2, p=Tl0.999GaPr0.001Se 2 and p-Tl0.995GaPr0.005Se2 are 2.165 eV, 2.164 eV and 2.155 eV and the ind irect band gaps are 2.110 eV, 2.122 eV and 2.128 eV, respectively. There is an abrupt change in the direct energy peak for p-TlGaSe2 in the temperatur e ranges 230-250 K, for p-Tl0.999GaPr0.001Se2 and p-Tl0.995GaPr0.005Se2 in the temperature ranges 195-215 K. On the other hand, indirect energy peaks for p-Tl0.999GaPr0.001Se2 and Tl0.995GaPr0.005Se2 are in the temperature ra nges 215-235 K.