Laser assisted processing of nanocrystalline (Ho0.05Y0.95) 2Ti2O7 films for infrared photonics

Abstract

The existence of new highly thermally and chemically stable active optical materials is a challenging task for current photonics research targeted on high-power lasers. Holmium-doped titanates crystallizing in the pyrochlore lattice, represent a promising class of materials. However, their high processing temperature limits their applications in integrated optical devices. This weakness can be overcome by laser assisted processing as an alternative to common heat-treatment. The amorphous thin films were prepared by a sol-gel method followed by a dip-coating process and densified in a rapid thermal annealing furnace. The densified films were annealed by a CO2 laser beam. The laser irradiation induced a crystallization process resulting in the formation of nanocrystalline (Ho0.05Y0.95)Ti2O7. The prepared film of a thickness 576 nm exhibited an optical transmission of 91.66% close to the maximum theoretical limit of a silica substrate. The film’s refractive index at 632 nm was 2.219. The formation of the nanocrystals caused the activation of the electronic transition 5I7→5I8 at 2 μm and the emission bands showed the distinct Starks splitting which is characteristic for (Ho0.05Y0.95)Ti2O7 phosphors. The presented approach can be used to prepare transparent luminescence films with tailored optical properties by CO2 laser treatment and together with direct laser writing can be used to prepared integrated optical waveguides as an alternative method to common heat-treatment processes.