Synthesis and photoluminescence of Eu3+ activated alkali mixed (Li, Na)Y(PO3)4 under VUV-UV excitation

Abstract

A series of LixNa1-xY(PO3)4: 10% Eu3+ samples (x = 0; 0.25; 0.5; 0.75; 1) were synthesized by a solid state reaction method. They were characterized at room temperature using X-ray diffraction and luminescence spectroscopy. The obtained powders crystallize in monoclinic systems with space groups C2/c and P21/n respectively for x = 1 and x = 0. However, according to XRD data, the LixNa1-x(PO3)4: Eu3+ material seems to be a mixture of the Li and Na homologues when x = 0.5. This situation has been considered as an option to broaden the VUV absorption instead of mixing of both Li and Na based compositions which has been considered as representative of the discrimination between the two extremes. The VUV excitation and emission spectra of as-synthesized compounds were measured. The broad bands near 200 nm in VUV excitation spectra are attributed to both contribution of overlapped O2− -Y3+ and O2− -Eu3+ absorption charge transfer states while the host absorption band is estimated at 150 nm. The emission spectra are dominated by three bands characteristics of the radiative de-excitation connecting the first excited state 5D0 of Eu3+ to the main 7F1, 7F2 and 7F4 manifolds of the ground state. Based on Judd–Ofelt (J–O) theory, the intensity parameters (Ω2 and Ω4) have been evaluated from the emission spectra.