K165
Short Notes
phys. stat. sol. (b) 31, K165 (1975)
Subject classification: 19; 2 2 . 6
Latvian State University, Riga
EPR of Copper Atoms in w q u a r t z
BY
I.K. AMANIS, J . G . KLIAVA, J . J . P U a N S , andA N. TRUPIIN
In honour of Prof. D r . Dr. h.c. P. GORLICH’S70th birthday
It is well known that copper gives r i s e to several optical absorption and luminescence bands in quartz (1 to 4 ) . The interpretation of these bands is complicated
0
+
by the possibility of different charge states for copper in quartz: Cu , Cu , Cu
The two states Cuo and Cu
++
++
.
a r e paramagnetic and the EPR method can be used to
investigate their role in the electron-hole pi.ocesses in quartz. The EPR signal of
of Cu
++
ions in quartz has been recently observed (3, 4). An EPR spectrum with
the hyperfine structure (HFS) constant 1700 G has also been reported (3). The au0
thoss of (3) have ascribed this spectrum to Cu atoms, but no evidence of such an
assignment has been given.
This note i s concerned with the EPR of a - q u a r t z doped with copper using the
electrodiffusion techniques. The crystals were irradiated with X-rays at liquid nitrogen temperature (77 K). The EPR spectra were taken in an x-band RE-1301
spectrometer with the microwave frequency 8 . 9 GHz. In addition, the optical absorption and luminescence spectra were measured by means of a setup described
elsewhere (5).
With the non-irradiated samples no EPR lines were found at 100 and 293 K , howe v e r , several absorption bands in the 4 . 7 to 8 . 5 eV region and luminescence bands
a t 2 . 4 and 3.4 eV were observed. Previously these bands have been assigned to Cu
+
ions (1, 2). This assignment i s now confirmed by the absence of any EPR signal associated with them.
After X-ray exposure the EPR spectrum presented in Fig. 1 was observed a t
-s
100 K. When the magnetic field H was applied along
d,
the three-fold crystalld-
graphic axis, the most intense part of the spectrum consisted of two four-line sets
-b
labelled a and f3 (see Fig. 1). F o r an arbitrary direction of H each of these lines
physica status solidi (b) 31
K166
a
I
a
I
I
I
I
I
1000
2 000
3000
GO00
501
H(G)
Fig. 1. EPR spectrum at 100 K of irradiated a-quartz doped with copper. The intense line at 3176 G arises from,the E ' centre (6) and the sextet at 3140 G
from aluminium-related centres (7)
was split into six equally intense components. Such behaviour i s characteristic of
EPR lines arising from a centre that occupies in the lattice of a-quartz six posi-
tions differing only with the orientation of their symmetry axes (7). The angular
dependences of the resonant magnetic field for the cy and
p
lines a r e described
by the following spin Hamiltonian with S = 1 / 2 , I = 3/2:
The rotational axes of g and A tensors coincide and make a small angle with the
Y axis of the Cartesian set of axes of a-quartz (see, for example, (7)for the no-
tation of axes). This results in six different orientations of the rotational axis of
tensors.
The components of g and A tensors were obtained by comparing the experimental
values of the resonant magnetic field with the theoretical ones, calculated for the
case when the Zeemann and hyperfine interactions a r e of the same order of magnitude (8). The following values were obtained:
for a a n d
p
lines, g, = 2.000 2 0.005, g,
cc
lines,Al = (3290 2 3O)MHz, A:
for
OL
for
p lines, AlP
= (3520 f 3O)MHz,
- g,,
- A,,OL
P
P
Al -All
= 0.002
2 0.0005 ,
= (176 2 2)MHz,
t
(189 f 2)MHz
.
Short Notes
K167
The values of g and A tensor components indicate the S type state of paramagnetic centres responsible for the observed EPR lines. The ratio of the intensities of%
p
lines , (2.40 0 . 8 ) : 1 closely approaches the abundance ratio of the two copper
63
isotopes Cu and 65Cu, 2.235: 1. (The small discrepancy between these two values
and
is probably due to the difference of the diffusion coefficients for the isotopes.) The
a : P
a
P
P
ratios AL /Al and (Al - A?/(A,
A,, ) agree within the experimental e r r o r with
-
the ratjo of the nuclear magnetic momenta for the isotopes 63Cu and 65Cu, 0.9335232:
: l(9). All these considerations permit us to assign the EPR lines we discuss to the
0
neutral copper atoms Cu ,(r: and
p
lines arising from the isotopes 63Cu and
65
Cu,
respectively.
Besides the EPR lines, discussed above, a new band a t 4 . 1 e V (2) appeared in
the optical absorption spectrum of a-quartz exposed to X-rays. Both the
(1:
and
P
lines and the induced optical band were bleached at the same r a t e by the irradiation
with 4 . 1 eV photons and simultaneously destroyed on warming to 244 K. Hence one
0
can conclude that the 4 . 1 eV absorption band a r i s e s from Cu atoms.
References
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(1)J.R
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(1974).
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2179 (1972).
(9) P.R. LOCHER, Phys. Rev. B lo, 810 (1974).
(Received August 13, 1975)