SC20
ICPLC 2002
SUBMILLIMETER EPR SPECTROSCOPY OF Ho3+ IONS IN
SYNTHETIC FORSTERITE
A. V. Gaistera A. A. Konovalovb, K. A. Subbotina, V. F. Tarasovb, E. V. Zharikova,c,
a) General Phyics Institute of RAS, Laser Materials and Technology Research Centre
b) Kazan Physical Technical Institute of RAS
c) D.I.Mendeleyev University of Chemical Technology of Russia
Synthetic forsterite doped by chromium ions is well known as an active medium
for tunable lasers in the near-infrared range. Laser oscillation is produced by Cr4+ ions
substituting tetrahedrally coordinated Si4+. There were found also Cr3+ and Cr2+ ions
replacing Mg2+ in octahedral positions M1 and M2 and exchange coupled pairs Cr3+Cr3+.
Here we present and discuss some results of the experimental study of impurity
Ho3+ ions in synthetic forsterite. The measurements were carried out at 4.2 K on a
submillimeter EPR spectrometer tunable in the frequency range 65 - 535 GHz and
magnetic fields between 0 and 1 Т. The spectrometer is based on tunable backward
wave oscillators as a source of microwave radiation and wide-band quasi-optic guide
[1]. Mg2SiO4:Ho3+ single crystals were grown from melt by the Czochralski technique
in slightly oxidizing atmosphere (nitrogen + 2 vol. % of oxygen). Samples had a
nearly cylindrical form with 1 cm in diameter and 1.5 cm length.
We observed three different paramagnetic centers formed by Ho3+ in forsterite.
The first center has two magnetically nonequivalent positions with principal
axes laying in the bc plane. Therefore we attributed this center to Ho3+ in the M2
position. For this center a characteristic hyperfine structure with eight narrow lines is
observed due to the 165Ho nuclear spin I= 7/2. Orientation dependences shown that for
this center principal magnetic axes are directed nearly parallel to the O(1) -O(2) line
of the M2 octahedron.
The hyperfine structure of the spectra belonging to the second center also has
eight hyperfine components. The line width of hyperfine lines was nearly 10 times
larger than that for the ion in the M2 position. There were observed four magnetically
nonequivalent positions for this center. Therefore we attributed this center to Ho3+ in
the M1 position. The z-axis of this center was directed nearly parallel to the line O(1)O(1) of the M1 octahedron.
The third center formed by Ho3+ ions has a complicated hyperfine structure
consisting of a large number of hyperfine components. We suggest that this center is
formed by a pair of Ho3+ ions connected by dipole-dipole interaction. Concentration
of these centers was much higher than one would expect if impurity Ho ions were
statistically distributed in the forsterite host. Possible structure of this center is
discussed.
1. V. F. Tarasov, G. S. Shakurov, Appl. Magn. Reson. 2 (1991).571-576.
International Conference on Physics of Laser Crystals, Kharkov Stary Saltov, 26.08. – 02.09.2002