Upconversion Luminescence Properties of Phase and Size Controlled NaLnF4:Yb3+, Er3+(Ln = Y, Gd) Nanoparticles

The upconversion luminescent nanoparticles of NaLnF(4) (Ln = Y, Gd):Yb3+, Er3+ were prepared through a facile modified solvothermal method, in which the phase (cubic or hexagonal) and size of the NaLnF(4) nanoparticles can be well controlled by adjusting Gd3+ content. The Gd3+ content dependent phase transformation and size change were systematically studied by the XRD and TEM measurements. The spectral measurement revealed that both the emission intensity and the intensity ratio of red (F-4(9/2) -> I-4(15/2)) to green (H-2(11/2), S-4(3/2) -> I-4(15/2)) are tunable, and a significant increase of the visible upconversion emission intensity can be realized by optimizing Gd3+ content at x = 0.25 under 980 nm excitation. Furthermore, the excitation power dependent red and green emission intensities of Er3+ were measured for various NaLnF(4) (Ln = Y, Gd):Yb3+, Er3+ nanoparticles with different Gd3+ content to investigate the influence of the phase and particle size on the upconversion luminescence properties. This research provided a new method to synthesize the upconversion nanoparticles with tunable luminescence properties by adjusting Gd3+ content.