Phosphorescence properties of sol–gel derived ruby measured as functions of temperature and Cr³⁺ content

Abstract

A novel approach for the contactless measurement of surface temperatures is to evaluate the temperature dependent phosphorescence properties of chromium doped aluminium oxide (ruby) coatings, such as phosphorescence intensity, spectral distribution, or the phosphorescence lifetime. However, these properties are also affected by the chromium content in the films. In the present study the phosphorescence lifetimes were studied for the first time as a function of the chromium content. We use a simple sol–gel depositing technique for the preparation of precisely doped ruby coatings in Si(100) substrates. These coatings (Cr-to-Al-ratios y between 0% and 6.8 at. %) are well suited for studying the influence of the chromium concentration on the phosphorescence properties: at room temperature (294 K), the phosphorescence intensity is strongly affected by the chromium doping (maximum at y∼1–1.5%) while the spectrum shifts only slightly with varying chromium content. The phosphorescence lifetime τ at 294 K remains constant with varying Cr³⁺ content below y∼1.1%, and decreases strongly above y∼1.1%. Thus, ruby doped with y∼1% seems to be most promising as a temperature sensor because it shows the highest phosphorescence intensity and a low variance in the phosphorescence lifetimes. Due to the latter property the temperature evaluation from τ is less affected by imprecise doping. The phosphorescence lifetimes of several sol–gel ruby coatings (y=1.1%) on Si(100) substrates were measured as a function of the temperature to be between 2.7 ms at 294 K and 4 μs at 833 K.