Luminescence of CaWO4, CaMoO4, and ZnWO4 scintillating crystals under different excitations

The luminescence spectra of CaW O4, CaMo O4, and ZnW O4 scintillating crystals were investigated in the temperature range 8-400 K. The excitation photon energy was varied from the ultraviolet (4.5 eV) to the hard x-ray region (35 keV). It is found that as the excitation energy decreases the relative intensity of the low-energy luminescence band, attributed to the extrinsic emission of defect centers in CaW O4 and CaMo O4 crystals, increases. This observation is interpreted in terms of the total absorption of incident radiation, i.e., the variation of the mean penetration depth of the photons with their energy. It indicates that the centers responsible for the extrinsic emission in the crystals with scheelite structure are mainly localized in a thin (∼100 nm) surface layer. On the other hand no noticeable changes with the excitation energy were found in the emission spectra of ZnW O4 crystals with wolframite structure. The possible implication of this finding is discussed. The light yield of the crystals is compared at low temperature using monochromatic x-ray excitation and it is shown that ZnW O4 has ∼10% higher light yield than CaW O4, while this parameter has a factor of 4 lower in CaMo O4. © 2005 American Institute of Physics