Anisotropic fundamental absorption edge of KTiOPO4 crystals

The fundamental absorption edge of KTiOPO4 (KTP) crystals has been investig ated with the polarization spectroscopy technique in the temperature range of 80-300 K. The Urbach rule parameters, E-0, alpha(0), sigma(0), and h ome ga, have been determined for the polarizations along each of the KTPs three crystallographic axes. A direct estimation of the KTP energy gap based on Urbach parameters has been made. A strong anisotropy of the gap has been fo und. The origin of the lowest energy electron excitations in KTP crystals a nd the possibility of self-trapping are discussed. (C) 2000 American Instit ute of Physics. [S0021-8979(00)07703-3].