Processing and properties of luminescent Cr3+ doped transparent alumina ceramics

Abstract

Transparent Cr2O3-doped alumina ceramics were prepared by slip casting, followed by pre-sintering in ambient atmosphere and hot isostatic pressing. The effect of dopant concentration on material properties, including microstructure and optical properties was evaluated. Real in-line transmittance in the range of 20–44 % was measured for the ceramics with the mean grain size <520 nm: the transmittance decreased with increasing grain size and Cr content. The excitation spectra consisted of two broad bands with maxima at 404 nm and 558 nm, corresponding to 4A2g → 4T1g and 4A2g → 4T2g transitions of Cr3+ ions in octahedral sites of α-Al2O3. The intensive deep red narrow emissions under violet/green light excitation, R-lines (2Eg → 4A2g transition), were observed at 692.5 nm and 693.8 nm, that are very close to ruby single crystal. The highest emission was achieved at the Cr3+ concentration of 0.4 at.%. The luminescence decay curves exhibited single-exponential behaviour with decay times of ∼3.6 ms.