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The quantum efficiency (QE) curves of five Philips XP2020Q photomultiplier tubes (PMTs) , one H amama t su R2059 PMT, and a Na-Salicylate coated glass window were determined using a calibrated Thorn EM1 9426 P M T as a reference. The QE of XP2020Q PMTs a t wavelengths smaller than 230 nm appears much better than the values specified by the manufacturer. Consequently, the often reported photon yield of 2000 photons/MeV for the fast component of the scintillation pulses from pure BaFz crystals determined with this tube is overestimated. Our results, obtained by means of calibrated equipment and using 662 keV-prays, yield a value of 1400 photons/hfeV.

The luminescence of cerium-doped barium fluoride crystals has been investigated as a function of wavelength and time. For excitation UV light, X-rays and gamma rays were used. The well known cross luminescence (CL) near 200 nm and self-trapped exciton luminescence (STE) near 300 nm, which are due to excitations of the host lattice, are observed at low cerium concentrations. For increasing cerium concentrations, the CL and STE emission is gradually replaced with cerium emission. Luminescence due to at least three different cerium related centres was found. The decay of the luminescence under gamma excitation is non-exponential. At low cerium concentrations, its duration is much longer than the decay time of the excited level of the predominant cerium centre. At higher cerium concentrations, the luminescence decays faster. These observations are explained in terms of an energy transfer model. The cerium luminescence due to energy transfer from CL and STE centres was calculated using the parameters obtained from experiment. Comparing the calculations to the observed photon outputs and decay curves leads to an interpretation of the luminescence mechanism in BaF2:Ce. Apart from radiative and dipole-dipole energy transfer from CL and STE centres to cerium centres, transfer from the STE to unknown centres also plays a role, as well as direct excitation of cerium centres by free or trapped electrons and holes.

Nd3+-doped LaF3, LiYF4, CsY2F7, BaY2F8 and BaF2 crystals were investigated. For scintillator applications, the characteristics of the fast Nd3+ 4f25d to 4f3 emission component is of interest. The effective 4f25d to 4f3 scintillation decay time under gamma irradiation was found to vary from 5 to 42 ns, depending on the host lattice. Light yields were determined under X-ray excitation. The 4f25d to 4f3 output from many samples was seriously affected by impurity absorptions. After correcting for these, an estimate was made of the maximum possible 4f25d to 4f3 light yield to be expected in very pure Nd3+-doped crystals. In neither of the cases was a 4f25d to 4f3 light yield of more than about 1000 photons per MeV of X-ray energy found. In addition to Nd3+ 4f25d to 4f3 emission, Nd3+ 4f3 to 4f3 and host emissions were also recorded at wavelengths shorter than 550 nm. A semi-quantitative model is given for the Nd3+ 4f25d to 4f3, 4f3 to 4f3 and host emission intensities.