摘要：Er(3+)/Yb(3+) co-doped Na5Lu9F32 single crystals with different concentrations of Yb(3+) ions were prepared to investigate their phase structure, up-conversion (UC) properties and mechanism of UC luminescence by Bridgman method. Under 980 nm near-infrared (NIR) excitation, three sharp UC emission bands topping at green ~525 nm, ~548 nm and red ~669 nm were obtained in Er(3+)/Yb(3+) doped Na5Lu9F32 single crystals which are attributing to the transitions of (2)H11/2 → (4)I15/2, (4)S3/2 → (4)I15/2 and (4)F9/2 → (4)I15/2, respectively. The quadratic dependence of pump power on UC emission indicated that two-photon process is in charge of the transition from excited state of Yb(3+) ions to lower state of Er(3+) ion in Na5Lu9F32 single crystals. The long-accepted mechanism for the production of red and green emissions through up-conversion (UC) under 980 nm excitation in Er(3+)/Yb(3+) co-doped materials apply in the Na5Lu9F32 host was displayed. The enhancement of the red emission was observed due to a cross-relaxation (CR) process of the form: (4)F7/2 + (4)I11/2 → (4)F9/2 + (4)F9/2. Furthermore, an ideal yellowish green light performance could be achieved with 1.0 mol% Er(3+) doped certain Yb(3+) concentrations samples, and its external quantum efficiency approached to 6.80% under 5.5 Wcm(-2) 980 nm excitation which can be applied in developing UC displays for electro-optical devices.
