Synthesis, crystal structure and luminescence properties of a new samarium borate phosphate, CsNa₂Sm₂(BO₃)(PO₄)₂

A new caesium sodium samarium borate phosphate, CsNa₂Sm₂(BO₃)(PO₄)₂, has been obtained successfully by the high-temperature solution growth (HTSG) method and single-crystal X-ray diffraction analysis reveals that it crystallizes in the orthorhombic space group Cmcm. The structure contains BO₃, PO₄, NaO₇ and SmO₇ polyhedra which are interconnected via corner- or edge-sharing O atoms to form a three-dimensional [Na₂Sm₂(BO₃)(PO₄)₂]_∞ network. This network delimits large cavities where large Cs⁺ cations reside to form the total structure. Under 402 nm light excitation, CsNa₂Sm₂(BO₃)(PO₄)₂ exhibits three emission bands due to the 4f→4f transitions of Sm³⁺. Furthermore, we introduced Gd³⁺ into Sm³⁺ sites to optimize the Sm³⁺ concentration and improve the luminescence intensity. The optimal concentration is Gd/Sm = 98/2. The luminescent lifetime of a series of CsNa₂Gd_2(1-x)Sm_2x(BO₃)(PO₄)₂ phosphors shows a gradual degradation of lifetime from 2.196 to 0.872 ms for x = 0.01-0.10. The Commission Internationale de l'Eclairage (CIE) 1931 calculation reveals that CsNa₂Gd_1.96Sm_0.04(BO₃)(PO₄)₂ can emit orange light under 402 nm excitation.