Luminescence, energy transfer, and up-conversion mechanisms of Yb3+ and Tb3+ co-doped LaNbO4

Novel green-emitting Yb3+ and Tb3+ co-doped LaNbO4 particles were prepared through a facile sol-gel and combustion method. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), thermogravimetric and differential thermal analysis (TG-DTA), up-conversion luminescence (UCL) with different powers and varied concentrations, and luminescent lifetimes were employed to test the prepared samples. The XRD data exhibit that a sample with high crystallinity can be acquired at 1000 degrees C. FE-SEM images show homogeneous and spherical grains after Yb3+ and Tb3+ are co-doped in the LaNbO4 samples. TG-DTA reveals that the LaNbO4 synthetic process is accompanied by a temperature increase. In our work, we utilize a 980 nm laser to excite Yb3+ ions to achieve the F-2(7/2) -> F-2(5/2) transition, and the LaNbO4:Yb3+, Tb3+ sample exhibits intense green emission. Luminescent spectra at different powers demonstrated the two-photon absorption process; meanwhile, the corresponding energy transfer mechanism from Yb3+ to Tb3+ and the emission of Tb3+ under 980 nm laser excitation was described via an energy level diagram. Moreover, concentration-dependent up-conversion luminescent properties were systematically explored, and it was confirmed that LaNbO4:0.15Yb(3+),0.02Tb(3+) exhibits the strongest luminescent properties. In particular, as the content of Yb3+ ions increases, the D-5(4) -> F-7(6) transition quickly becomes stronger, resulting in the emitted color shifting from green to blue. Therefore, the emitted color can be tuned by adjusting the content of Yb3+ ions. The excellent up-conversion emission properties of the obtained samples allow for their potential application in the fields of 3D display technologies and solid-state lasers. (C) 2017 Elsevier B.V. All rights reserved.N