Solution processed highly transparent nitrogen-doped carbon quantum dots/ZnO hybrid thin films : A study on structural and enhanced UV emission

We deposited the highly transparent nitrogen-doped carbon quantum dots (N-CQDs) incorporated ZnO (N-CQDs/ZnO) hybrid thin films by sol–gel spin-coating process. TEM studies show a narrow size distribution of hydrothermally synthesized N-CQDs in the range of 2.5 to 3 nm. The SEM images ascertain the formation of ZnO nanoparticles upon incorporation of N-CQDs in the hybrid films. Raman studies show the hexagonal wurtzite structure of spin-coated ZnO thin film and ascertain the presence of incorporated N-CQDs adsorbed on the surface of ZnO in the hybrid films. The incorporated N-CQDs get adsorbed onto the surface of ZnO crystallites and control its size at nanoscale in the hybrid thin films. The XPS study also confirms the incorporation of nitrogen-doped CQDs and the existence of chemical interaction (chemisorption) between N-CQDs and ZnO nanoparticles, making the pathways for favorable energy transfer between N-CQDs and ZnO in the hybrid thin films. The band-edge emission (383 nm) of ZnO film increases for the increasing concentration of N-CQDs upon UV excitation (325 nm), showing the non-radiative UV energy transfer from N-CQDs to ZnO in the hybrid thin films along with the contribution of photoluminescence emission of N-CQDs in the visible region.