Optical properties versus temperature of Cr-doped γ- and α-Al2O3: Irreversible thermal sensors application

A thorough investigation by X-ray diffraction, UV-vis and luminescence spectroscopy is carried out to demonstrate how the chromium content of alumina matrices impacts the temperature of the gamma -> alpha irreversible phase transition. The Cr3+ contents influence slightly the phase transition temperature but control the brightness of the powders. Nice colorimetric contrasts from green to pink are observed between the two allotropic forms. Furthermore, drastic changes of the spectral distribution and of the intensity of luminescence are observed, thus allowing to use this pigment as a both thermochromic and luminescent thermal sensor. Additional measurements at low temperature revealed that the Cr3+ emission of the gamma-Al2O3 matrix is constituted by a large band. A configurational diagram schematic approach suggested for the first time that this emission is due to spin-allowed T-4(2)->(4)A(2) transition on this largely investigated gamma-Al2O3 compound. (C) 2016 Elsevier B.V. All rights reserved.