Piezo-spectroscopic behavior of the emission bands of α-alumina in the 13900–14250 cm− 1 spectral range

摘要

The emission spectrum of α-alumina in the spectral range between 13900 and 14250 cm−1 is characterized by several bands which are much weaker than the two intense and sharp R1 and R2 bands appearing at 14400 and 14430 cm−1, respectively; these latter are known as Ruby lines and they are the emission bands used in the Ruby laser. Furthermore these bands shift in frequency with stress (Piezo-Spectroscopic effect). In this paper, for the first time, the stress-dependent peak frequency of the weaker bands in the 13900–14250 cm−1 range is calibrated, and the results are presented as Piezo-Spectroscopic coefficients. The calibration is performed by reporting the frequency shift of each investigated band as function of varying stresses. The stresses, residual in nature, are obtained by fabricating composite materials where α-alumina is mixed in various amounts with (i) Ceria-Stabilized Tetragonal Zirconia Polycrystals (Ce-TZP) and (ii) silicon carbide, SiC. The composite materials are prepared at high temperature (1500°–1800°C); due to the difference in thermal expansion, upon cooling to room temperature α-alumina develops compressive and tensile stresses, when mixed with Ce-TZP and SiC, respectively. The stress values necessary for the calibration are obtained from the frequency shift of the R2 band, using its well-established Piezo-Spectroscopic coefficient (7.6 cm−1/GPa). Then the newly obtained Piezo-Spectroscopic coefficients of the bands in the 13900–14250 cm−1 range are tested to retrieve the stresses in two sets of composites; finally the stress values are compared with those obtained in the same samples from the frequency shift of the R2 band. The comparison shows a very good agreement, thus providing evidence that the bands in the 13900–14250 cm−1 range can be used to monitor stresses in α-alumina-based materials.