Upconversion luminescence of Er3+ doped Y2O3 and Gd2O3 nanophosphors

The luminescence process and mechanism of Er3+ doped Y2O3 and Gd2O3 nanophosphors are investigated with focus on their upconversion luminescence properties. Here the strong up-conversion (UC) emissions of both Y2O3:Er3+ nanoparticles prepared by combustion with EDTA and Gd2O3:Er3+ nanospheres synthesised by multistep chemical reaction using urea have been measured at room or low temperatures. The downward-conversion luminescence spectra in visible and near infrared region have been assigned from the transitions in the energy level system of Er3+ion. For Y2O3:Er3+nanoparticles, the upconversion luminescent intensity depends on excitation power at 980 nm have properly indicated the two photon process which are the calculated slope values of main transitions in Er3+ions: 2H11/2-4I15/2, 4S3/2-4I15/2and 4F9/2-4I15/2 are 2.07, 1.72, 1.87 (0.5% Er) and 2.32, 1.82 and 2.07 (Er 1.0%) respectively. The integral intensity of the red band is smaller than that of the green band in the upconversion emission of nanoparticles Y2O3 doped with Er3+ with 0.50, 1.00 and 1.50%. However it was the integral intensity of red emission bands that dominated in Gd2O3: 1% Er3+. The lifetimes of the band in green colour peaked at 562 nm upon excitation at 380 nm in Y2O3:Er3+ with 0.50, 1.00 and 1.50%, and have shown the two sequent time decay processes, the shorter and the longer, both in millisecond scale, 0.14 ms (0.5%); 0.28 ms (1.00%) and 0.13 ms (1.50%) and 4.49 ms (0.5%); 6.89 ms (1.00%) and 5.16 ms (1.50%), respectively. For the nanoparticles Gd2O3: 1% Er the intensity decrease of the upconversion emission peaked at 562 nm with only a single process with a decay time of 1.24 ms. Both nanophosphors Y2O3 and Gd2O3 doped with Er3+ are promising materials to develop multifunctional units for medical applications.