Urbach' s rule and optical properties for $TlGaS_2$

Özet

Absorption measurements were carried out on $TlGaS_2$ sample in the temperature range between 10 and 320 K in 10 K steps. There is an abrupt change in the Urbach energy at 180 K and 280 K and steepness parameter at 120 K and 220 K .Obtained from the changing of the Urbach energy, these may be phase transition temperatures. The phonon energies calculated for $TlGaS_2$ is 19.7$ \pm $5 meV.