Blue shift of Tm3+ upconversion owing to Nd3+ in yttrium oxide powders pumped by pulsed red laser

Tm3+:Y2O3 powder prepared by combustion synthesis exhibits blue emission centered at λ ∼ 450 nm, corresponding to 1D2 → 3F4 transition of Tm3+, when the sample is irradiated by a pulsed (5 ns, 10 Hz) red laser operating at λ ∼ 690 nm. The blue emission band shifts to λ ∼ 480 nm, corresponding to 1G4 → 3H6 transition of Tm3+, when Nd3+ is added to the sample. When the laser is tuned to λ ∼ 680 nm, the blue shift effect is not observed. The shifting effect is explained based on single shot laser excitation and energy transfer mechanisms involving Tm3+ and Nd3+ ions.