Gd3+-Doping Effect on Upconversion Emission of NaYF4: Yb3+, Er3+/Tm3+Microparticles

beta-NaYF(4)microcrystals co-doped with Yb3+, Er3+/Tm3+, and Gd(3+)ions were synthesized via a hydrothermal method using rare-earth chlorides as the precursors. The SEM and XRD data show that the doped beta-NaYF(4)form uniform hexagonal prisms with an approximate size of 600-800 nm. The partial substitution of Y by Gd results in size reduction of microcrystals. Upconversion luminescence spectra of microcrystals upon 980 nm excitation contain characteristic intra-configurational ff bands of Er3+/Tm(3+)ions. An addition of Gd(3+)ions leads to a significant enhancement of upconversion luminescence intensity with maxima at 5 mol % of dopant.