•Co-doped (Y0.99−xHo0.01Ybx)2Ti2O7 nanophosphors were fabricated by gel-combustion method.•The effect of calcination and Yb3+ doping on upconverting spectra of nanophosphors was studied.•The dependence of upconverting intensity on the excitation power was examined.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.

Er3 +/Yb3 + codoped pyrochlore-type (Y0.99-xEr0.01Ybx)2Ti2O7 (x = 0, 2.5, 5.0, 7.5, 10.0 and 12.5 mol%) nanocrystals have been successfully prepared by the sol–gel process with citric acid as chelator. The samples annealed at 800 °C for 1 h exhibit good crystallinity and narrow size distribution with average size of 20–30 nm. Upon 980 nm excitation at room temperature, green (at ~ 525 and 545 nm) and red (at ~ 660 nm) upconversion emissions were observed, which are ascribed to the (2H11/2, 4S3/2) → 4I15/2 and 4 F9/2 → 4I15/2 transitions, respectively. And also, it has been found that the annealing temperatures and the Yb3 + ion doping concentrations have greatly influenced on the upconversion luminescence intensity. The results show that Y2Ti2O7 is an excellent host material for efficient upconversion nanophosphors.Highlights► (Y0.985-xEr0.01Ybx)2Ti2O7 nanocrystals are prepared at relative low temperatures. ► Bright green and red upconversion emission can be clearly observed with naked eyes. ► The maximum upconversion intensity can be obtained at 7.5 mol% of Yb3 + ion doping. ► The ratio of red to green emission intensity increases with the rise of Yb3 + doping.