Optical absorption spectrum of excited Cr3+ ions in MgAl2O4 spinel crystals

The absorption spectrum of Cr³⁺ ions in the magnesium spinel MgAl₂O₄ was determined for crystals excited by strong optical pumping, and for unexcited crystals. The absorption cross section of the ⁴A_2g level was found to be 2.5 · 10^–20 cm², which was an order of magnitude smaller than that for ruby. The spectrum obtained for the excited crystals consisted of five absorption bands with maxima at 250, 325, 390, 440, and 550 nm. The absorption cross section for the maximum of the first band was ~2 · 10^–18 cm². The absorption cross sections at the maxima of the other bands were (1 – 2.5) · 10^–20 cm². An energy scheme for Cr³⁺ ions in MgAl₂O₄ was derived.