Sulfur: an alternative to mercury for UV emission in low-pressure low-power fluorescent discharges

Abstract

The objective of this exploratory study is to demonstrate that sulfur can offer an advantageous alternative to mercury for the production of UV photons in fluorescent discharges not only in terms of environment and health impacts, but also in terms of Stokes shift energy losses for the conversion of UV photons by luminophors into visible light. The experiments are performed in surface-wave plasma columns sustained at the output end of a coaxial applicator by microwaves at 2.45 GHz frequency and 10 W applied microwave power. After introducing 10 mg sulfur in argon at 1 Torr, it can be observed that most of the emission spectrum due to sulfur is maximum in the UV range between 300 and 400 nm, well above the 253.7 nm resonant peak line met with mercury in low-pressure discharges. Therefore, by comparison with mercury, the Stokes shift is considerably reduced in the case of sulfur. By surrounding the silica discharge tube with a segment of commercial fluorescent tube coated inside with luminophors, the UV spectrum of sulfur appears quite efficiently transferred into visible light.