Enhancement of up-conversion luminescence of Y2Ti2O7:Yb3+/Ho3+ nanocrystals by incorporating Li+ ions

Abstract

Tri-doped (Y0.915Ho0.01Yb0.075Lix)2Ti2O7 (x = 015.0 mol%) nanocrystals were fabricated via a facile glycinecombustion 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 980nm 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.