Bridgman growth and luminescence properties of Na2Mo2O7 crystal

This research presents a Bridgman method for the crystal growth of disodium dimolybdate (Na₂Mo₂O₇, NM₂O) crystals and understanding their luminescence mechanism. An NM₂O crystal with a size of 23 * 23 * 90 mm³ was grown using the vertical Bridgman method. The cleavage of the NM₂O crystal was analyzed by X-ray diffraction and scanning electron microscopy, which showed that the crystal cleaves along the (0 0 1) plane and the cleavage planes appear in a step pattern. Its luminescence properties were studied using transmission spectra and laser-stimulated luminescence spectra, which showed that the transmittance of a 5 mm thick sample reaches 85 % in the range of 500–700 nm with the absorption cutoff edge at 360 nm, resulting in the optical band gap of 3.35 eV. Under excitation of a 278 nm laser beam, the sample exhibited dual-peak emission, typically at around 598 nm and 673 nm, consistent with radioactive annihilation of the self-trapped exciton on [MoO₆]⁶⁻ and [MoO₄]²⁻ groups respectively. Also the luminescence at low temperatures were measured and discussed. All results can benefit the crystal growth and application to the 0νββ experiments for the functional material.