A high-resolution absorption spectrum of the lowest $4f\to 5d$ transition of ${\mathrm{Ce}}^{+3\mathrm{}}$ in Ca${\mathrm{F}}_2$ is presented showing a rich vibronic structure. The observed structure leads to an entirely different interpretation of the spectrum from that proposed by Loh.

• Received 31 May 1973

DOI:https://doi.org/10.1103/PhysRevB.8.4910