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

Er ³⁺ -doped silicate planar waveguides are important for the fabrication of integrated optics amplifiers. This paper presents a study of reversible photoluminescence (PL) quenching in Er ³⁺ -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 H ₂ O, studied by infrared spectroscopy, plus the role of film porosity in the PL quenching phenomenon.