Sols of lanthanide-doped zirconia with the general formula Zr(0.90)Ln(0.10)O(2-x) were prepared by an inorganic sol-gel method. The sols were characterized for particle size distribution, and the gels and heated gels were characterized for structure crystallite size and lattice parameter. Thin films of these materials were deposited on quartz substrates, and were crystalline, continuous and single phase as-deposited, with a cubic fluorite structure as shown by X-ray diffraction. The films were annealed to 600 and 1050 degreesC after deposition and found to be transparent in the region between 400 and 1100 nm, the crystalline structure becoming tetragonal at 1050 degreesC. The refractive index increased with increase in annealing temperature and decreased with ionic size of the dopant, varying between 1.53 for the largest cation, and 1.65 for the smallest cation at 600 degreesC, and between 1.77 and 1.90 over the same range at 1050 degreesC. Optical band gap calculations also showed a similar ionic size and temperature dependence with the optical band gap varying from 5.55 to 5.70 eV.