Blue shift of optical band-gap in LiNbO3 thin films deposited by sol-gel technique

Lithium niobate (LN) thin films were deposited on quartz substrates by sol-gel technique. The measured absorption and photoluminescence spectra show that the band structure of LN thin films is direct unlike indirect band-gap in bulk LN and the optical band-gap of these LN thin films was measured to be 4.7 eV which is ~ 1 eV greater than that for stoichiometric bulk LN. The dependence of the blue shift of band-gap on several parameters like quantum confinement, composition (Li:Nb ratios of LN thin films) and strain was also investigated. The results obtained show that the large blue shift in band-gap of LN thin films is primarily due to strain in the film.