Enhanced Red Emission of Na5Lu9F32: Eu3+ Single Crystal by Introducing of GdF3

Abstract The bulk Na 5 Lu 9 F 32 single crystals with high quality serial Eu 3+ /Gd 3+ co‐doped were grown by an ameliorative Bridgman technique. The measurement of X‐ray diffraction (XRD) and analysis of Rietveld refinement were implemented to validate the crystal phase. The Eu 3+ doped Na 5 Lu 9 F 32 single crystal emits intense red emission at 611 nm excited by 394 nm light. The intensity of 1.8 mol % Gd 3+ doped sample is boosted by 3.56 times compared with the un‐doped one. The doping of Gd 3+ ions replace competitively Lu 3+ lattice sites with Eu 3+ ions. Thus, they cause the lattice distortion and reduction of symmetry, enabling Eu 3+ ions to overcome their 4 f forbidden transitions. The change of Eu 3+ ion local environment induced by Gd 3+ ion doping was explored by the Eu 3+ emission spectra and the variations of ratios between red and orange emission intensities (R/O). The fluorescence lifetime indicates that the introduction of GdF 3 decreases the probability of non‐radiative transitions and increases the fluorescence lifetime. These results demonstrated that the Na 5 Lu 9 F 32 : Eu 3+ single crystal doped with an appropriate concentration of GdF 3 is a type of promising red emission single crystal for related optical devices of detector and laser due to its strong red emission, high transparency and high physico‐chemical stability.