Theoretical studies for investigating the quantum size effects in bandgap and luminescence properties have excluded the lattice variations and the relevant impacts that may occur in the nanoscale regime.This work addresses the lattice dimension of highly crystalline Zn1-xCoxO nanorods and its impacts on the electronic structures.For x=O,the intrinsic yellow emission was taken as a probe to monitor the corresponding quantum size effects in band modifications.It is found that with increasing nanorod diameter,the lattice volume decreased linearly,while the peak maximum of the yellow luminescence shifted towards lower energies with a magnetitude smaller than the calculated value from bandgap theorem.For x>O,with increasing Co2+ dopant concentration,the lattice volume enlarged considerably,which is associated with the enhanced repulsive interactions of defect dipole moments on the wall surfaces.This lattice modification produced a significant decrease in bandgap energies with its magnitude that followed the relationship,AEg =AEo· (e-x/ B-1),where x and B are Co2+ dopant concentration and a constant,respectively.The abnormal bandgap energies were indicated to originate from the sp-d exchange interactions that are proportional to the square of lattice volume.