Vapourtec has made a set of 9 wavelength filters available for the UV-150 reactor photochemical reactor. These filters are intended for use together with the medium pressure mercury lamp. The radiant output of the medium pressure mercury lamp provides a broad range of wavelengths from 220 nm up to 600 nm. This makes the medium pressure mercury lamp the most versatile light source but for many reactions the unwanted wavelengths can cause many side reactions or even decomposition of the product. The wavelength filters allow the selection of only the desired wavelengths, the wavelengths that promote only the intended reaction.
The nine wavelength filters are of two types; long-pass filters and band-pass filters.
There are five long-pass filters available. The transmission of these filters is shown in the figure below. In traditional photochemistry Pyrex or quartz are commonly used as long-pass filters. In the figure below the Pyrex filter is shown as the light blue transmission curve. The advantage of the other filters is to allow the detailed exploration of the wavelengths to determine the optimum wavelength to drive the reaction while eliminating unwanted products.
There are four band-pass filters available. The transmission of these filters is shown in the figure below. Band-pass filters are used to provide the wavelength range of interest while eliminating most of the unwanted radiant heat energy. By using the band-pass filters it is possible to achieve low reaction temperatures even when using the high power medium pressure mercury lamp. For visible light sensitized photochemical reactions, filter #6 is particularly useful. For direct photochemical reactions requiring wavelengths in the range 260 to 340 nm, filter #2 is very effective, cutting out almost all the infra-red wavelengths.