Nanocrystalline Zn2TiO4 films for distributed Bragg's reflectors operating in near infrared region

Abstract

We present a generic sol-gel approach for the preparation of a distributed Bragg reflector (DBR) based on combining nanocrystalline Zn2TiO4 with amorphous SiO2 xerogel films. We determined the effects of the annealing temperatures on the structural and optical properties of nanocrystalline Zn2TiO4 films. The increasing size of nanocrystals and film's density caused a regular growth of the films' refractive indices at 632 nm from the value of 1.837–1.960. The acquired data were applied to design the DBR with tailored reflectance at 980 nm and the data predicted by the theoretical model were compared with experimental transmission and reflection spectra. Although the high optical losses caused by the Rayleigh scattering were observed at short wavelengths, the prepared films were fully transparent above 600 nm. The uniform dielectric structure reflecting over 97% of incident light at 980 nm was prepared from eight Bragg's pairs. The normalized spectral bandwidth was about 0.22. We proved the nanocrystalline films exhibiting scattering in UV-VIS spectral region can be used for the construction of the distributed Bragg's reflectors operating in near infrared region. The presented approach can be easily extended to other nanocrystalline films allowing the integration of nanocrystalline luminophores into advanced photonic structures.