Wavelength-shifting materials for the use in RICH detectors - p-terphenyl and tetraphenyl-butadiene revisited

P-terphenyl (PT) and tetraphenyl-butadiene (TPB) in form of thin films have been investigated as possible wavelength shifting material for application in Ring Imaging Cherenkov (RICH) detectors. Films of different thickness were evaporated onto borosilicate windows of photomultiplier tubes (PMT) and the quantum efficiency of the modified PMTs was determined as a function of wavelength. Gain factors for the number of measured photoelectrons in dependence on the cutoff wavelength (energy) for application in Cherenkov counters were established. Using PT, a strong increase in quantum efficiency between 200 nm and 300 nm was observed leading to gain factors as high as 1.71 ± 0.11 for a cutoff energy of 6.2 eV. Due to strong absorption in the wavelength range between 300 nm and 400 nm, TPB shows inferior results. No significant thickness dependence was observed for films thicker than 600 nm. Film morphology and wavelength dependent fluorescence was measured to back the results. Simulations encourage the use on flat panel multi-anode photomultipliers.