Effect of Gd, La, Lu Co-Doping on the Morphology and Luminescent Properties of NaYF:Sm Phosphors.

The series of luminescent NaYF:Sm nano- and microcrystalline materials co-doped by La, Gd, and Lu ions were synthesized by hydrothermal method using rare earth chlorides as the precursors and citric acid as a stabilizing agent. The phase composition of synthesized compounds was studied by PXRD. All synthesized materials except ones with high La content (where LaF is formed) have a β-NaYF crystalline phase. SEM images demonstrate that all particles have shape of hexagonal prisms. The type and content of doping REE significantly effect on the particle size. Upon 400 nm excitation, phosphors exhibit distinct emission peaks in visible part of the spectrum attributed to G→H transitions (J = 5/2-11/2) of Sm ion. Increasing the samarium (III) content results in concentration quenching by dipole-dipole interactions, the optimum Smconcentration is found to be of 2%. Co-doping by non-luminescent La, Gd and Lu ions leads to an increase in emission intensity. This effect was explained from the Sm local symmetry point of view.