Performances of Metachrome II as scintillator for the far and vacuum ultraviolet spectral region

A couple of metachrome II samples having different thicknesses are tested as the downconverter fluorescent layer in the far and vacuum UV (58 to 297 nm). Their performance is compared with that obtained by tetraphenyl butadiene, another scintillator widely used in this spectral region. The emission angular distribution, the fluorescent spectrum, and the absolute conversion efficiencies are measured for all of the phosphors. The results show some peculiar effects related to the incident angle with the surface where the phosphors are deposited; moreover, they show that tetraphenyl butadiene offers higher efficiency than metachrome II, but also that the latter shows good efficiency throughout the investigated spectral region. This fact indicates that interesting applications can be performed with metachrome II when it is used as the downconverter phosphor with silicon detectors whose spectral response matches well the emission spectrum of metachrome II. For example, this could enable having CCDs sensitive in the extreme UV region, without requiring very expensive and sophisticated UV-sensitive treatments.