Luminescence of ZnMoO₄ Crystals Developed for the LUMINEU Double Beta Decay Experiment

Scintillation efficiency of ZnMoO 4 crystals is one of the main characteristics for application in cryogenic double beta decay experiments. Luminescence of ZnMoO 4 crystals developed from deeply purified molybdenum under X-ray irradiation of different doses was studied in the temperature interval from 1.4 K to 295 K. Emission spectra, dependence of luminescence intensity on dose and temperature, phosphorescence and thermally stimulated luminescence were investigated. Two emission bands were identified: recombination luminescence at ~ 600 nm and exciton luminescence at ~ 500 nm. We have found that concentration of shallow traps in the material is much greater than the concentration of deep traps. Furthermore only shallow traps absorb a small part of the luminescence and cause the low scintillation efficiency of the sample.