Fabrication of Y2Ti2O7:Yb3+,Ho3+ nanoparticles by a gel-combustion approach and upconverting luminescent properties

Yb3+, Ho3+ co-doped pyrochlore-structured (Y0.99−xHo0.01Ybx)2Ti2O7 (x = 0, 2.5, 5.0, 7.5, 10.0 and 12.5 mol%) nanoparticles (NPs) were successfully fabricated via a gel-combustion approach. The products as-obtained were characterized by various techniques, i.e. X-ray diffraction, transmission electron microscope, Fourier transformed infrared spectra and upconverting spectra. The results indicate that the bright green (∼540 nm) and red (∼660 nm) emissions are observed in Y2Ti2O7:Ho3+,Yb3+ NPs under the 980 nm excitation, which is ascribed to the radiative transitions (5F4,5S2) → 5I8 and 5F5 → 5I8 of Ho3+ ions, respectively. It is also found that the calcining temperature and Yb3+ ion doping level have a great influence on the upconverting spectra of (Y0.99−xHo0.01Ybx)2Ti2O7 NPs. The emission intensities increase initially and then fall down from 800 to 1000 °C. The optimum doping level of Yb3+ ions is 7.5 mol%, and the intensity of upconverting emissions for (Y0.915Ho0.01Yb0.075)2Ti2O7 NPs is enhanced by the fold of 32 compared to the Yb3+-free samples. The dependence of upconverting intensity on the excitation power reveals the contribution of two photons to both the green and red upconverting process under lower excitation power, and the possible upconverting mechanisms have been proposed accordingly.