Optical Properties of Anionic Gold Centers in CsBr and CsI Crystals

Abstract

Optical studies are for the first time performed on Au-centers in Cs-halides. Absorption spectra above 90 K and emission and excitation spectra down to 13.9 K are investigated for CsBr: Au-and CsI : Aucrystals. In both the crystals four absorption bands exist called D,, C, B, and A and two emission bands called B' and A' in the order of decreasing energy. In CsBr, a luminescence resembling c( emission known in other alkali systems IS also observed, but it seems not to be peculiar to Au-centers because of its dependence on the thermal treatment of the specimens. The King-Van Vleck factors, 2, which are obtained by analyzing the optical data are 2.5 (CsBr) and 2.2 (CsI), which are larger than unity as in the case of all other alkali halides: Au-so far investigated. Dans CsBr, une luminescence qui ressemble a emission 2 sachant dans autre systeme alcalin est observe, mais il ne semble q'est particulier pour centres Au-, parce que dependant de traitement thermique de specimens. La facteurs de King-Van Vleck 3, qui sont obtenus a I'aide de I'analyse a data optique sont 2,5 (CsBr) et 2,2 (CsI), qui sont plus grandes que unite, comme ceux obtenus jusqu'ici pour les centres Au dans autre halogenure alcalin.

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

“…The values for the A and B absorption bands agree with those reported in the previous paper. 20) The values for the C absorption bands are reported for the first time in the present work.…”

“…20) In the previous paper, the A, B, C, and D absorption bands due to the Au À center and their relaxed luminescence bands were observed in the ultraviolet (UV) energy region at low temperatures. From the relative positions of the absorption bands and their relative intensity ratio, the Coulomb energy, the exchange energy, the spin-orbit interaction energy, and the King-Van Vleck parameter, which characterize the ns 2 centers, were obtained for the Au À center in CsBr and CsI crystals.…”

“…11) A number of theoretical and experimental studies have been performed on cationic ns 2 centers such as Tl þ , In þ , and Pb 2þ . [1][2][3][4] As compared with the cationic ns 2 centers, the anionic ns 2 centers such as Au À , Ag À , and Cu À are comparatively less studied, [12][13][14][15][16][17][18][19][20][21] especially the Au À center in cesium halide crystals.…”

Creation of CsAu nanoclusters by UV‐light irradiation on CsBr:Au– crystals

“…The CsBr crystals doped with the Au -ions are prepared as described previously [21]. First, the addition of the Au + ions into pure single crystals of CsBr purchased from Union Material Inc. (Japan) was performed by a diffusion reaction of AuCl powder with the crystals.…”

“…Therefore, in the absorption spectrum before the irradiation of a UV light, the absorption bands called A, B, C, and D appear in the energy region below the fundamental absorption edge of the CsBr crystal [21]. The A, B, and C bands arise from the transitions from the 6s 2 to 6s6p states in the isolated Au -ion.…”