Luminescence Characteristics of Tb Doped ZnO Nanoparticles Synthesized by Sol-Gel Route

Structural and optical properties of the Tb doped ZnO nanoparticles with average diameter ≈5 nm have been investigated systematically. The absorption study shows an increase in the band gap as Tb is incorporated with ZnO nanoparticles. The influence of Tb doping on the photoluminescence spectrum of the nanoparticles, which comprises of a UV luminescence (UVL) and a broad green luminescence (GL) band, is found to depend strongly upon the Tb concentration and the ambient conditions. Intensity of the green luminescence band under atmospheric condition is found to increase with the Tb concentration for all the Tb doped ZnO nanoparticle samples investigated here. On the other hand, under vacuum condition, the GL intensity decreases to almost complete suppression with increasing Tb concentration up to Tb mole-fraction x ~ 0.02. We conjecture that Tb is incorporated at the surface which though binds more surface groups under atmospheric condition, thereby enhancing GL, but weakly, which facilitates their easy removal under vacuum and hence the suppression of GL.