For the uninitiated, all quartz has not been created equal. Although GE 124 quartz has been used widely by customers of SPI Supplies, and for the most part is quite acceptable. There is a subset of researchers who, to put it bluntly, are not satisfied with GE 124 and want a quartz like product with even lower impurity levels and therefore lower fluorescence but higher transmission values in the UV.
The "solution" to the "problem" is to use products fabricated not from GE 124 but from Corning® 7980 which is a synthetic flame fused silica, which has inherently lower trace impurities present. Both are "quartz" materials but unlike GE 124, which starts out literally with beach sand, and with all the impurities imaginable that would be found in sand and it is refined from there. For the production of Corning 7980, a gaseous form of a silane compound which can be made to ultrapure levels that is reacted with a flame, resulting in a quartz product. With all of the properties of GE 124 but has far superior transmittance properties because of the higher level of purity.