Abstract
Tri-doped (Y0.915Ho0.01Yb0.075Lix)2Ti2O7 (x = 0–15.0 mol %) nanocrystals were fabricated via a facile glycine–combustion approach. The crystal structure, morphology and up-conversion spectra of the as-obtained products were investigated using X-ray powder diffractometer (XRD), transmission electron microscope (TEM), spectrophotometer pumped by 980 nm diode laser, and Fourier transform infrared spectrometer. XRD results demonstrated that, owing to the flux effect of Li+ ions, the crystallization temperature of matrix Y2Ti2O7 decreased when compared to Li+-undoped samples. TEM results showed the average particle of (Y0.79Ho0.01Yb0.075Li0.125)2Ti2O7 nanocrystals calcined at 800°C for 1.0 h was estimated to be ∼50 nm. It was also found that up-conversion emissions were strongly dependent on the calcining temperature and Li+ ion concentration. Compared with the Li+-free Y2Ti2O7:Yb3+/Ho3+ samples, the green and red emission intensity of nanocrystals tri-doped with 12.5 mol % Li+ was enhanced by 10.2 and 4.8 times, respectively. The emission increase should be mainly ascribed to the distortion of local symmetry around Ho3+ ions by Li+-doping. In addition, the pump power dependence of integrated intensity suggested that both green and red emission was two-photon population process.
