Optical properties of high refractive index thin films processed at low-temperature

This study reports on the first development of high refractive index thin film materials processed at temperatures not greater than 100 °C. Three materials were synthesised by the sol–gel technique, each employing different transition metal precursors (niobium, tantalum and vanadium alkoxides). The optical properties of these materials were characterised by ellipsometry and the propagation losses at 638 nm were measured by the prism coupling method. It is shown that refractive indices as high as 1.870, 2.039 and 2.308 are obtained from niobium-, tantalum- and vanadium-based materials respectively, attributed to the influence of the transition metal atomic size on the condensation reactions.

► Synthesise of high refractive index materials with Nb, Ta and V alkoxides is shown.
► Thin films were characterised by ellipsometry and prism coupling method.
► Refractive indices as high as 1.870, 2.039 and 2.308 measured at 635 nm are reported.