Influence of wavelength-shifting films on multianode PMTs with UV-extended windows

Wavelength-shifting (WLS) films were applied on UV-extended front windows of multianode photomultiplier tubes (MAPMTs) in order to increase the sensitivity of the MAPMTs at shorter wavelengths. The WLS material contained p-Terphenyl as photoactive component, which absorbs shorter wavelength photons (<300nm) and re-emits fluorescence photons around 350 nm, i.e., at the maximum of the PMTs׳ sensitivity. The films were applied by means of dip-coating and the film performance was studied with respect to quantum efficiency, film homogeneity, and crosstalk on the MAPMTs. Using WLS-film-covered MAPMTs in a gaseous Ring Imaging Cherenkov detector, the number of detected photoelectrons per ring increased by up to 21% in an in-beam test.