Interpretation of the Optical Spectrum of Yb3+ in CdF2 with the Aid of ESR Spectroscopy

Abstract

The optical absorption spectra of Yb³⁺ in CdF₂ and of Yb³⁺ in CdF₂ in the presence of various codopants such as Na⁺, Y³⁺, and Eu³⁺ were recorded, and the oscillator strengths of the main absorptions of the Yb³⁺ in the 10 000‐cm⁻¹ region were calculated. Also, the electron spin resonance (ESR) spectra of Yb³⁺ in CdF₂ and Yb³⁺ in CdF₂ in the presence of Na⁺, 2% Y³⁺, and 10% Y³⁺ were recorded. Noncubic spectra were observed only in the case of the Yb³⁺–Na⁺–CdF₂ and Yb³⁺–10% Y³⁺–CdF₂ samples. The former noncubic spectrum was interpreted assuming a rhombic distortion with the major distortion axis along the [110] direction, while the latter could not be interpreted due to the broadeness of the absorptions. From the results of these measurements and the comparison to the optical spectra of Yb³⁺ in other systems, it has been concluded that the previous interpretation of the optical spectrum of Yb³⁺ in CdF₂ is incorrect. It is suggested that the main absorption line at 10 250 cm⁻¹ is not due to an internal $\mathrm{f–f}$ transition but is due to some other mechanism. Possible mechanisms are proposed based on some of the unusual physical properties of trivalent rare‐earth ions in CdF₂. The interpretation of the optical spectra assuming the absorptions at 10 395 and 10 870 cm⁻¹ are the main $\mathrm{f–f}$ transitions gives a reasonable fit to the theoretical calculations.