EPR of Yb3+ ions in Ba1−xLaxF2+x mixed crystals

Abstract

Electron paramagnetic resonance (EPR) spectra of impurity Yb 3 § ions (about 0.1 at.%) in mixed crystals BaF:(I -x) plus LaF3(x) have been investigated for different values of the concentration x at a frequency of about 9.5 GHz by both continuous-wave (CW) EPR and electron spin echo methods. A spectrum of trigonal symmetry with a complex hyperfine structure is observed in "pure" BaFz:Yb 3 § (x = 0). Upon admixture of small amounts of LaF3 (x = 0.001), additional EPR lines arise with intensities increasing with the increase of x up to 0.005. These lines are attributed to trigonal centers including two rare-earth ions and two compensating fluorine ions. A further increase of x results in a decrease of the total EPR spectrum intensity, andat x > 0.05 the CW resonance becomes practically unobservable. This may be due to the formation of rare-earth ion clusters with paramagnetic Yb 3. ions occurring in domains with a disordered structure of surroundings resulting in very broad EPR lines, which cannot be registered by CW EPR. Indeed, very broad (not less than 1 kG) EPR lines were observed by the electron spin echo method for concentrations x > 0.02.

EPR of rare-earth ion clusters in mixed crystals Ba1−x La x F2+x doped with Yb3+ Ion

“…To continue our previous investigations [7] we have measured the EPR spectrum of Yb 3 § ions in the mixed crystal (BaF2)l_x_y(LaF3)x(YbF3)y with x = 0.01, y = 0.001 by the electron spin-echo (ESE) method (W-band, v = 94.9 GHz) at T = 2 K. The EPR spectra were recorded by measuring the two-pulse ESE amplitude as a function of the applied magnetic field. The spectra for several orientations of an applied magnetic field close to the trigonal axis (B II Ca) are shown in Fig.…”

“…Intensive lines O~ and 02 were observed already for "pure" BaF a (x = 0), so they were attributed to the well-known single trigonal center Yb-F (O-center with gll = 2.77, g• = 3.75) [3,7,8]). These lines are accompanied by the hyperfine structure due to Yb ~7~ isotopes (natural abundance of 14.4%, nuclear spin I = 1/2, hyperfŸ interaction parameter Aj : 887.2 MHz [9]) and Yb 173 (natural abundance of 16.2%, I = 5/2, A: =-243.3 MHz).…”

“…3) and hinders the picking out of extra lines appearing for concentrations of x > 0. Therefore, in our previous work [7] we were able to separate and discuss in detail only the trigonal cluster La-FYb-F (A-center, g~l = 2.248, g• = 4.023), which gives rise to A l and A 2 lines. In the W-band, hyperfine components are very close to the main lines (for I = 0) and the hyperfine structure is not resolved (Fig.…”

“…7. Therefore, it is possible to consider the trigonal part of the crystal potential acting on the RE 3+ ion asa correction to the cubic potential and to calculate g-factors within the framework of the perturbation theory.…”

“…Recently we have investigated EPR spectra of the mixed crystals (BaF2)~_x• (LaF3)x:0.1%Yb with 0 _< x _< 0.05 at a frequency of about 9.5 GHz [7]. A number of extra lines emerging at x > 0 was attributed to trigonal clusters La-F-Yb-F in which the Yb 3+ ion has two compensators in the nearest interstitial positions along the threefold axis (Fig.…”