Optical Properties of Au^-Centers in CsBr and CsI Single Crystals

Abstract

The temperature dependence of the absorption and luminescence spectra has been investigated for Au À centers in CsBr and CsI single crystals with the CsCl structure. In addition to the A, B, C, and D absorption bands, the A 0 and B 0 luminescence bands caused by the intraionic transitions in the Au À ion are observed at 12 K. The luminescence bands are characterized by a small Stokes shift and a narrow halfwidth, reflecting a weak electron-phonon interaction. Furthermore, the photoexcitation at the energies corresponding to the A, B, and C absorption bands induces luminescence bands in the visible energy region. The A 0 , B 0 , and visible luminescence bands change with temperature while complementing each other. The features of the Au À centers in cesium halides and the nonradiative transitions between the relaxed excited states are discussed.

Comparison of Luminescence Properties of CsI Crystals Activated with Ag-, Au-, and Tl+Ions at Room Temperature

“…However, we consider the origin to be the radiative transition from the relaxed excited states of the Au À ion located at the off-center position in the lattice site. 10) The luminescence spectra under excitation at 193 nm, which is shorter than the band gap of CsI, are not identical to those under excitation at the absorption bands due to the activated centers. Excitation in the wavelength region of the band-to-band transition of CsI could bring about luminescence bands due to other impurity ions and/or defects in addition to activated centers.…”

“…The pronounced absorption bands peaking at 340 nm for CsI:Ag À and at 265 nm for CsI:Au À correspond to the C absorption band formed by the intraionic transitions from the 1 S 1 ground state to the 1 P 1 excited state in activated ions. [7][8][9][10][11] From the intensities of the C absorption bands, the concentrations of Au À and Ag À ions in the crystals were estimated to be on the order of 1 Â 10 17 /cm 3 using the Smakula-Dexter formula. 12,13) The A absorption band formed by the intraionic transition from the 1 S 1 ground state to the 3 P 1 excited state is observed with a peak at 380 nm for CsI:Au À and at 300 nm for CsI:Tl þ .…”

“…The luminescence properties of CsI:Ag À and CsI:Au À crystals have been investigated mainly at low temperatures and under excitation in the energy region below the band edge of CsI. [7][8][9][10][11] In this study, we have investigated the luminescence properties of CsI:Ag À and CsI:Au À under excitation in the energy region above the band edge of CsI at room temperature (RT). The luminescence properties of CsI:Ag À and CsI:Au À are evaluated and compared with those of CsI:Tl þ .…”