The electrodeless discharge lamp: a prospective tool for photochemistry

This work expands our previous research on an original photochemical reactor consisting of the electrodeless discharge lamp (EDL) inside a reaction mixture that generates ultraviolet radiation in the microwave (MW) field. The effects of temperature MW output power of the reactor, and EDL envelope material, were already published [P. Müller, P. Klán, V. Církva, J. Photochem. Photobiol. A: Chem. 158 (2003) 1]. Now we report on the emission characteristics (250-650 nm) of various EDLs containing different fill materials (Hg, HgI2, Cd, I2, KI, P, Se, and S). While distinct line emission peaks were found for mercury, cadmium and phosphorus fills, iodine, selenium and sulfur-containing EDLs emitted continuous bands. Sulfur-containing EDLs are proposed for phototransformations that are of environmental interest due to the emission flux comparable to solar terrestrial radiation. It is concluded that the right choice of EDL envelope fill material can be very useful in planning an efficient course of photochemical process without necessity of filtering off the undesirable part of the UV radiation by other tools, such as glass or solution filters or monochromators. Quantum efficiency measurements of the Norrish type II reaction were accomplished to compare usefulness of the EDLs in photochemical applications. Sulfur and phosphorus-containing EDLs were found as the most efficient sources of UV radiation.