Absorption Spectra of Cr³⁺ in Al₂O₃ Part A. Theoretical Studies of the Absorption Bands and Lines

TLDR

Cr³⁺ in Al₂O₃ is studied within crystalline field theory, accounting for trigonal distortion and spin‑orbit coupling to describe its excited states and optical transitions. The authors analyze the initial splittings and optical anisotropies of the broad quartet band and sharp doublet lines, including Zeeman effect predictions for the latter. Their calculations assign the U, Y, R₁, R₂, B₁, and B₂ bands and lines, explain the observed g‑shifts in the Zeeman patterns, and link optical absorption data to paramagnetic resonance measurements.

Abstract

In the frame-work of the crystalline field theory, the excited states of Cr 3+ in Al 2 O 3 and the optical transitions to these states are studied taking into account the effect of trigonal field and spin-orbit interaction. Initial splittings and optical anisotropies of the broad band (transitions to quartet states) and the sharp lines (transitions to doublet states) are examined. For the sharp lines, the Zeeman effect is also examined and the Zeeman patterns are predicted. Comparing these theoretical results with those of the experimental ones given in Part B, the assignments of U , Y bands and R 1 , R 2 , B 1 , B 2 lines have been established. It is shown that the g -shifts of the excited doublets observed in the Zeeman patterns can also be explained under such assignments. It is also shown that the experimental data of the optical absorption can be reasonably connected to those of the paramagnetic resonance absorption.