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.

► Polycrystalline LiNbO3 (LN) films deposited on quartz by sol–gel technique. ► Band-gap in LN films observed to be direct and large blue shift of 1 eV observed. ► Dependence of blue shift on quantum confinement, Li:Nb ratio and strain investigated. ► Results show that the large blue shift in band-gap is primarily due to strain.