Multifunctional Y₂0₃:Yb³⁺/Tm ³⁺/Li⁺ nanocrystals with enhanced near-infrared to near-infrared upconversion photoluminescence

Rare earth ion-doped Y₂O₃ nanoparticles are attractive for biological imaging applications due to their non-toxicity, resistance to photobleaching, and possibility for upconversion. Y ₂O₃:Yb³⁺/Tm³⁺ nanocrystals display photoluminescence (PL) with a peak at ∼811nm if excited at ∼980nm. This Near-Infrared to Near-Infrared (NIR-to-NIR) upconversion (UC) process provides deeper light penetration into biological specimen and results in high contrast optical imaging due to absence of an autofluorescence background and decreased light scattering. Here, we report that NIR-to-NIR UC PL intensity of Y ₂O₃:Yb³⁺/Tm³⁺ nanocrystals are enhanced by doping with different Tm³⁺ ions and Li⁺ ions concentration. When the Tm³⁺ ions concentration reaches 0.25 mol%, the NIR-to-NIR UC PL intensity is the strongest. and the NIR-to-NIR UC PL intensity of Y₂O₃:5 mol % Yb³⁺ ions, 0.25mol% Tm³⁺ ions and 5mol% Li⁺ ions is maximum, which is more that about 14 times than that of no doped Li⁺ ions. This material may show promise for use as probes for biological imaging.