Optical studies of hydrogenbonded dielectrics TlH₂PO₄

Abstract

We have for the first time investigated optical properties of thallium dihydrogen phosphate TlH2PO4 (TDP) up to vacuum ultraviolet energy region at low temperature. The remarkable dispersion‐like structures due to the first exciton transitions are observed around 5.8 eV above the fundamental absorption edge at 5.2 eV. The origin of the first excitons in TDP is ascribed to the cationic transition from 6s2 to 6s 6p electronic states in Tl+ ions. In the higher energy region, characteristic peak structures appear at 15.6 and 16.7 eV. The peak structures are attributed to the core excitons based on the transitions from 5d106s2 to 5d96s26p states in Tl+ions. A broad luminescence band with a large Stokes shift is observed at 2.9 eV, stimulated efficiently at the first exciton transition region. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)