A series of Eu³⁺/Gd³⁺ co-doped Na₅Lu₉F₃₂ single crystals are prepared by Bridgman technique method. The emission intensity at 611 nm of Eu³⁺ ion in the single crystal increases obviously as Gd³⁺ doping upon excitation of 394 nm. The intensity of 1.8 mol % Gd³⁺ doped sample is boosted by 3.56 times compared with the un-doped one. The substitution of Gd³⁺ for the Lu³⁺ lattice position causes a variation of the Eu³⁺ ion local environment confirming from the change of red and orange emission intensities and enlargement of the unit cell, which are the reasons for the emission enhancement. The Na₅Lu₉F₃₂: Eu³⁺ single crystal doped with an appropriate concentration of GdF₃ is a type of promising red emission single crystal for related optical devices of detectors and laser.

Abstract

The bulk Na₅Lu₉F₃₂ single crystals with high quality serial Eu³⁺/Gd³⁺ 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 Eu³⁺ doped Na₅Lu₉F₃₂ single crystal emits intense red emission at 611 nm excited by 394 nm light. The intensity of 1.8 mol % Gd³⁺ doped sample is boosted by 3.56 times compared with the un-doped one. The doping of Gd³⁺ ions replace competitively Lu³⁺ lattice sites with Eu³⁺ ions. Thus, they cause the lattice distortion and reduction of symmetry, enabling Eu³⁺ ions to overcome their 4f forbidden transitions. The change of Eu³⁺ ion local environment induced by Gd³⁺ ion doping was explored by the Eu³⁺ emission spectra and the variations of ratios between red and orange emission intensities (R/O). The fluorescence lifetime indicates that the introduction of GdF₃ decreases the probability of non-radiative transitions and increases the fluorescence lifetime. These results demonstrated that the Na₅Lu₉F₃₂: Eu³⁺ single crystal doped with an appropriate concentration of GdF₃ 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.