Yb3+, Tm3+ Co-doped β-NaY1-xGdxF4 (0 ≤ x ≤ 1.00) microcrystals: Hydrothermal synthesis, evolution of microstructures and upconversion luminescence properties

Yb3+, Tm3+ co-doped beta-NaY1-xGdxF4 (0 <= x <= 1.00) microcrystals have been synthesized via a facile hydrothermal method. The influences of the concentration of Gd3+ on the morphology, grain size and upconversion luminescence of the as-synthesized co-doped beta-NaY1-xGdxF4 crystals have been investigated in detail. Powder Xray diffraction results confirm that the obtained beta-NaY1-xGdxF4 crystals are pure hexagonal solid solution. Scanning electron microscope results indicate that the morphology of the final obtained beta-NaY1-xGdxF4 crystals gradually changes from hexagonal prism to sphericity with increasing x, and the grain size monotonically decreases accordingly. The upconversion emission intensity of Tm3+ in the beta-NaY(1-x)GdxF(4) microcrystals increases initially and then decreases sharply with increasing x, giving the maximum at x = 0.04. The observed upconversion emission intensity located at 475 nm in co-doped beta-NaY0.74Gd0.04F4 microcrystal is 1.5 times greater than that of the co-doped beta-NaYF4 microcrystal. A superior upconversion host matrix of beta-NaY(1-x)GdxF(4) solid solution can be obtained at the feasible concentration of Gd3+ (0 < x <= 6%).