Optical Properties of Gold Atoms in γ-Irradiated Organic Solid Solutions at 77 K

Abstract

Au0 atoms were produced via the electron capture of Au+ ions in γ-irradiated solid solutions of MTHF at 77 K. The optical absorption bands observed in the regions of UV and NUV are ascribed to Au0. The steady-state emission and excitation spectra were measured by photoexcitation at 73 K before and after γ-irradiation of the solid solutions containing [Au+] ions. The two-dimensional time-resolved emission spectra were also investigated by photoexcitation at λexc = 337, 380, and 420 nm by using an N2 laser and dye lasers. A set of five emission bands of 385, 430, 480, 520, and 580 nm and another set of emission bands at 456, 482, 484, and 520 nm were observed. The latter set of emission bands showed such characteristic structures as the mirror image of the absorption bands of Au0 in the rare gas matrixes. The emission band at 430 nm observed before γ-irradiation was confirmed to be phosphorescence due to Au+ with a lifetime of about 625 ms. A part of the emission band of 385 nm observed after γ-irradiation was also due to phosphorescence consisting of two components with lifetimes of 146 and 461 ms. Three types of exciplexes (Au+·Ln)*, (Au0·Ln...Au+)*, (Au0·Ln)*, and the excited gold atom (Au0)* are proposed for all the emission bands including phosphorescence. The excited gold atoms in 2P1/2 and 2P3/2 states participate mainly in the formation of these emissive exciplexes. The formation mechanism for these species is also presented.