PNNL

Abstract

Strong anti-Stokes luminescence of Mn2+ is observed in ZnS:Mn2+ bulk and nanoparticles. The anti-Stokes emission band excited at 767 nm is red-shifted from the Stokes emission excited at 300 nm with the bulk and the particles encapsulated in zeolite-USY as exceptions. In the nanoparticles, the decay lifetimes of the anti-Stokes emission excited at 767 nm are shorter than the 300 nm excited Stokes lifetimes, while in the bulk, the two decays are almost identical. When the Stokes emission is obtained by excitation at 383.5 nm, which is the sum energy of two-photons at 767 nm, the emission spectra and the lifetimes of the two types of luminescence are almost identical. The power dependence of the Stokes emission is linear, while that of the anti-Stokes emission is quadratic. Based on those observations along with the temperature dependence of the anti-Stokes luminescence intensity, it is concluded that two-photon excitation is responsible for the anti-Stokes luminescence of Mn2+ in ZnS:Mn2+ nanoparticles.