Reversible photoluminescence quenching in Er3+-doped silica–titania planar waveguides prepared by sol–gel

Er3+-doped silicate planar waveguides are important for the fabrication of integrated optics amplifiers. This paper presents a study of reversible photoluminescence (PL) quenching in Er3+-doped silica–titania planar waveguides, prepared by sol–gel processing. The infrared absorption and PL spectra of these waveguides at 1.5 μm are reported as a function of different heat treatments and time of exposure to various atmospheres. The corresponding emission lifetimes have also been measured in selected cases. Several samples have shown a decrease in the 1.5 μm PL peak intensity, after a few days in air at RT and a longer decrease when kept in an ultrasonic water bath. This change is found to be reversible, however, as long as a subsequent heat treatment at temperatures as low as 200 °C is performed on the same samples. In addition, when these are kept under a controlled atmosphere with low moisture contents (such as in liquid nitrogen, or in a controlled atmosphere glove-box), there is a decrease in the rate at which the PL decreases. A heat treatment in a vacuum furnace, at a relatively high temperature (∼700–900 °C), is shown to prevent most of the PL quenching. We examine the possible mechanisms involved, including the effects of residual OH groups and atmospheric H2O, studied by infrared spectroscopy, plus the role of film porosity in the PL quenching phenomenon.