Photophysics of Gaseous UF₆ in the UV: Energy Balance Through Quantum Efficiency Measurements

Abstract

Experimental results were recently published on the fluorescence of gaseous UF₆ excited in the near UV by a tunable dye laser [1, 2, 3, 4, 5, 6]. Several features of this fluorescence are now well established. The visible fluorescence spreads from 400 to 460 nm with a maximum around 420 nm: the shape of the spectrum is independent of pressure or of wavelength of excitation [4, 6]. The Stern-Volmer plot has a saturation like behaviour for the high pressures [4, 5]. This result although found on the experimental points in [2, 3] was not taken into account by Benetti and Andreoni. The excitation spectrum of fluorescence drops down below 380 nm to give almost no emission for an excitation below 360 nm [1, 4, 6]. We give here a systematic study of absolute quantum yieds of fluorescence of UF₆. After a description of the experimental apparatus we study the effects of three parameters on the quantum efficiency and decay times: room temperature self quenching, temperature effects between 20° C and 100° C and collisions with rare gas. All these results are taken in account in a tentative phenomenological model presented at the end.