Photoluminescence properties of perspective bolometric crystals Na2Mo2O7 and Na2W2O7 grown by low-thermal-gradient Czochralski technique

Abstract Alkaline molybdate and tungstate crystals are promising bolometric materials for the search for rare events, especially for the search for neutrinoless double beta decay. Fluorescent thermometry for remote measurement of the temperature needs materials that demonstrate a significant change in the decay time of luminescence with a change in temperature. This paper presents the results of temperature-induced changes investigation in the photoluminescence of undoped tungstates and molybdates of the general formula Na2M2O7 (M = Mo, W) in the temperature range of 77–300 K. Analyzing changes in the emission and excitation spectra, as well as in the decay kinetics allowed assessing the prospects of Na2Mo2O7 and Na2W2O7 crystals as materials for luminescence lifetime thermometry. The emission color chromaticity coordinates of Na2Mo2O7 and Na2W2O7 crystals were calculated and shown on Commission Internationale de L'Eclairage (CIE 1931). Correlated color temperature and color purity for both investigated crystals were estimated. For Na2Mo2O7 correlated color temperature is equal to 1672 K and color purity is 95%, for Na2Mo2O7 correlated color temperature is equal to 6460 K and color purity is 27%. The CIE investigation results show that Na2Mo2O7 expose strong red emission with color purity close to color purity of the monochromatic light sources.