Investigation on the upconversion properties of Ln_2O_2S∶Yb,Pr (Ln=Y, La) nanocrystals

The upconversion luminescence properties of Ln2O2S∶Yb,Pr(Ln=Y, La) nanocrystals prepared by ethanol assistant solution combustion method have been investigated. The as-prepared Ln2O2S∶Yb,Pr nanophosphor exhibit intense blue-green emission under 980nm IR pump in daytime by the naked eyes. Y2O2S∶Yb,Pr exhibits maximum emission with peak at 514nm, and La2O2S∶Yb,Pr shows the strongest emission at 508nm. It can be attributed to the Pr3+ ions 3P0 to 3H4 allowed electric dipole transition. The proximity of the 5d orbitals to the 4f states of Pr3+ results in a strong dependence of the f-f transitions on the environment in which Pr3+ is embedded. Thus, the upconversion luminescence of Pr3+ ions 3P0 to 3H4 transition shows a strong dependence of different host lattices.