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.

Ligand Effects on ESR and Optical Properties of Gold Atoms in γ Irradiated Organic Solid Solutions at 77 K

“…This is similar to the case for AuClP(C 2 H 5 ) 3 / MTHF solutions. 8 In addition to these bands, a broad absorption band was observed after γ irradiation at 320-400 nm with a peak at 340 nm and a long tail extending to 400 nm for AuCl/ MTHF solution without HCl as shown by the dotted line in Figure 2A(a). In the previous case for AuClP(C 2 H 5 ) 3 /MTHF solutions, 8 the broad absorption band appeared in the NUV region of 320-380 nm in the case of higher Au + concentration.…”

“…The optical absorption spectra for AuCl/MTHF solutions without and with HCl obtained and shown in Figure 2A(a) and (b) in this study are almost similar to the previous spectra for AuClP(C 2 H 5 ) 3 /MTHF solutions 8 except for two points: first, an absorption band at 320-330 nm was observed clearly for the present cases before γ irradiation, which was hardly observed for the previous ones, and second, the absorption bands were observed at 340-380 nm in the difference spectra, which were not for AuClP(C 2 H 5 ) 3 /MTHF solutions. 8 According to the fact that the absorption band of the Cl 2 in gas phase lies at 330 nm,…”

“…The procedures of sample preparation were almost the same as in our previous studies. 8 To remove ESR signals due to H atoms produced and trapped in a Suprasil quartz tube, the drops of solutions were directly dropped into liquid nitrogen to produce spherical glasses of about 1.5 mm in diameter. 9 For each solution, 10 or more spheres were transferred into a vial of 1 cm 3 volume in liquid nitrogen and irradiated by γ rays at 77 K. After γ irradiation, the spherical samples were transferred into unirradiated Suprasil quartz ESR tubes in liquid nitrogen and used for measurement after photobleaching as mentioned above.…”

“…As a series of our studies on Ag 0 and Cu 0 atoms, we have already been studying Au 0 atoms. 6,8 The first ESR report on Au 0 atoms was presented by us for the two sets of (solutes/ solvents) combinations of AuClP(C 2 H 5 ) 3 /2-methyltetrahydrofuran (MTHF) and AuCN/10 M NaOH. 6 We have confirmed the formation of Au 0 atoms in the solid solutions by observing the characteristic ESR lines of Au 0 .…”

Effects of UV Irradiation on ESR and Optical Properties of Cu(II) Ions in Organic Solid Solutions Containing CuCl at 77 K

“…As a fundamental research to elucidate the function and effects of metal ions and/or atoms in biological systems, we have been investigating the ESR and optical properties of 1B metal atoms produced radiation-chemically by reducing their mono cations in solid solutions [4][5][6][7][8][9][10][11][12]. In the series of our previous studies, formation of metal atoms, Cu 0 , Ag 0 and Au 0 in irradiated solid solutions containing their mono cations were evidenced by ESR spectra that exhibited duplicate quartets [10], duplicate doublets [8] and quartet [12], respectively.…”