Negative thermal quenching of the 3.338 eV emission in ZnO nanorods

We investigate the negative thermal quenching behavior of the 3.338 eV emission in ZnO nanorods. A correlation between the 3.338 eV and the 3.368 eV (surface exciton) emissions is determined from temperature-dependent photoluminescence. The activation energies of the 3.338 eV emission, obtained using an approximated multi-level model, indicate an trap state between the two surface exciton emissions. The present study demonstrates a nondestructive and easy method to understand the surface effects on the optical properties of semiconductor nanostructures.