INTERPRETATION OF OPTICAL SPECTRUM OF YB3+ IN CDF2 WITH AID OF ESR SPECTROSCOPY

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 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 f-f transitions gives a reasonable fit to the theoretical calculations.