Crystalline phase detection in glass ceramics by EPR spectroscopy
The advances of EPR spectroscopy for the detection of activators as well as determining their local structure in the crystalline phase of glass ceramics is considered. The feasibility of d-element (Mn²⁺, Cu²⁺) and f-element(Gd³⁺, Eu²⁺) ion probes for the investigation of glass ceramics is discussed....
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irk-123456789-1759922021-02-04T01:26:40Z Crystalline phase detection in glass ceramics by EPR spectroscopy Antuzevics, A. Rogulis, U. Fedotovs, A. Popov, A.I. Динамика кристаллической решетки The advances of EPR spectroscopy for the detection of activators as well as determining their local structure in the crystalline phase of glass ceramics is considered. The feasibility of d-element (Mn²⁺, Cu²⁺) and f-element(Gd³⁺, Eu²⁺) ion probes for the investigation of glass ceramics is discussed. In the case of Mn²⁺, the informationis obtained from the EPR spectrum superhyperfine structure, for Gd³⁺ and Eu²⁺ probes – from the EPR spectrum fine structure, whereas for Cu²⁺ ions the changes in the EPR spectrum shape could be useful. The examples of EPR spectra of the above-mentioned probes in oxyfluoride glass ceramics are illustrated. 2018 Article Crystalline phase detection in glass ceramics by EPR spectroscopy / A. Antuzevics, U. Rogulis, A. Fedotovs, A.I. Popov // Физика низких температур. — 2018. — Т. 44, № 4. — С. 449-454. — Бібліогр.: 39 назв. — англ. 0132-6414 PACS: 76.30.–v, 61.72.Hh http://dspace.nbuv.gov.ua/handle/123456789/175992 en Физика низких температур Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України |
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Динамика кристаллической решетки Динамика кристаллической решетки |
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Динамика кристаллической решетки Динамика кристаллической решетки Antuzevics, A. Rogulis, U. Fedotovs, A. Popov, A.I. Crystalline phase detection in glass ceramics by EPR spectroscopy Физика низких температур |
| description |
The advances of EPR spectroscopy for the detection of activators as well as determining their local structure in the crystalline phase of glass ceramics is considered. The feasibility of d-element (Mn²⁺, Cu²⁺) and f-element(Gd³⁺, Eu²⁺) ion probes for the investigation of glass ceramics is discussed. In the case of Mn²⁺, the informationis obtained from the EPR spectrum superhyperfine structure, for Gd³⁺ and Eu²⁺ probes – from the EPR spectrum fine structure, whereas for Cu²⁺ ions the changes in the EPR spectrum shape could be useful. The examples of EPR spectra of the above-mentioned probes in oxyfluoride glass ceramics are illustrated. |
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Article |
| author |
Antuzevics, A. Rogulis, U. Fedotovs, A. Popov, A.I. |
| author_facet |
Antuzevics, A. Rogulis, U. Fedotovs, A. Popov, A.I. |
| author_sort |
Antuzevics, A. |
| title |
Crystalline phase detection in glass ceramics by EPR spectroscopy |
| title_short |
Crystalline phase detection in glass ceramics by EPR spectroscopy |
| title_full |
Crystalline phase detection in glass ceramics by EPR spectroscopy |
| title_fullStr |
Crystalline phase detection in glass ceramics by EPR spectroscopy |
| title_full_unstemmed |
Crystalline phase detection in glass ceramics by EPR spectroscopy |
| title_sort |
crystalline phase detection in glass ceramics by epr spectroscopy |
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Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України |
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2018 |
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Динамика кристаллической решетки |
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http://dspace.nbuv.gov.ua/handle/123456789/175992 |
| citation_txt |
Crystalline phase detection in glass ceramics by EPR spectroscopy / A. Antuzevics, U. Rogulis, A. Fedotovs, A.I. Popov // Физика низких температур. — 2018. — Т. 44, № 4. — С. 449-454. — Бібліогр.: 39 назв. — англ. |
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Физика низких температур |
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2025-07-15T13:37:03Z |
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| fulltext |
Low Temperature Physics/Fizika Nizkikh Temperatur, 2018, v. 44, No. 4, pp. 449–454
Crystalline phase detection in glass ceramics
by EPR spectroscopy
A. Antuzevics, U. Rogulis, A. Fedotovs, and A.I. Popov
Institute of Solid State Physics, University of Latvia, 8 Kengaraga, LV-1069 Riga, Latvia
E-mail: andris.antuzevics@gmail.com
Received September 17, 2017, published online February 26, 2018
The advances of EPR spectroscopy for the detection of activators as well as determining their local structure
in the crystalline phase of glass ceramics is considered. The feasibility of d-element (Mn2+, Cu2+) and f-element
(Gd3+, Eu2+) ion probes for the investigation of glass ceramics is discussed. In the case of Mn2+, the information
is obtained from the EPR spectrum superhyperfine structure, for Gd3+ and Eu2+ probes – from the EPR spectrum
fine structure, whereas for Cu2+ ions the changes in the EPR spectrum shape could be useful. The examples of
EPR spectra of the above-mentioned probes in oxyfluoride glass ceramics are illustrated.
PACS: 76.30.–v Electron paramagnetic resonance and relaxation;
61.72.Hh Indirect evidence of dislocations and other defects.
Keywords: electron paramagnetic resonance, paramagnetic ions, glass ceramics.
1. Introduction
An actual problem for the development of glass ceramics
is ensuring that the majority of dopant ions embed the crys-
talline phase of the material. Crystalline phases in glass ce-
ramics are usually detected by x-ray diffraction (XRD)
measurements and visualized by transmission electron mi-
croscopy (TEM) photographs, however, these methods do
not provide the essential information about the activator
local structure. Absorption and luminescence spectra, on
the other hand, can indicate changes in the local environ-
ment around the luminescence centres, however, structure
sensitive magnetic resonance spectroscopy techniques
should be employed to reveal the detailed nature of defects
in glass ceramics. Electron paramagnetic resonance (EPR)
is one of the most convenient and informative methods for
the study of point defects in crystals and glasses [1–11],
however, there has been only a limited number of applica-
tions to glass ceramics [12–21].
A choice of optimal temperature is necessary to ensure
the best EPR signal intensity and avoid temperature caused
line broadening in the spectra. For this reason EPR meas-
urements are usually done at cryogenic temperatures, e.g.
at liquid nitrogen boiling point (77 K).
The present paper provides a review of EPR results of
paramagnetic probes studied in glass ceramics as well as
our recent data on Mn2+, Cu2+ and Gd3+ ions in
oxyfluoride glass ceramics.
2. Experimental
Glasses were prepared by the conventional melt
quenching technique. Batches of 8 g (see Table 1) were
mixed and melted at (1450 ± 10) °C in covered alumina
crucibles and quenched by pouring the melts onto a stain-
less steel plate. The glass ceramics were obtained by an
isothermal heat treatment of the transparent precursor glass
(PG) at the indicated temperature. The sample abbreviation
includes the paramagnetic probe (Mn, Cu or Gd) as well as
the crystalline phase of the glass ceramic samples (C —
CaF2, S — SrF2, B — BaF2, N — NaLaF4). The last num-
ber in the sample abbreviation is the heating temperature in
°C. For example, Mn_C_700 is the glass ceramic obtained
after heating the Mn_C_PG (precursor glass) composition
sample at 700 °C for 1 h.
X-ray diffraction (XRD) measurements with
PANalytical X’Pert Pro diffractometer were made to iden-
tify the crystalline phases present in glass ceramics.
© A. Antuzevics, U. Rogulis, A. Fedotovs, and A.I. Popov, 2018
A. Antuzevics, U. Rogulis, A. Fedotovs, and A.I. Popov
Table 1. Compositions used for glass preparation
Abbreviation Composition
Mn_C
Cu_C
Gd_N
Gd_S_01
Gd_S_10
Gd_S_40
46SiO2–20Al2O3–8CaCO3–25CaF2–0.1MnO
46SiO2–20Al2O3–8CaCO3–25CaF2–0.1CuO
63SiO2–7Al2O3–16Na2CO3–9NaF–5LaF3–0.1GdF3
40SiO2–25Al2O3–15Na2CO3–1EuF3–19SrF2–0.1GdF3
40SiO2–25Al2O3–15Na2CO3–1EuF3–18SrF2–1.0GdF3
40SiO2–25Al2O3–15Na2CO3–1EuF3–15SrF2–4.0GdF3
EPR spectra were measured at 77 K with a conventional
X-band spectrometer (≈ 9.1 GHz). The magnetic field was
callibrated using a polycrystalline DPPH reference — an
organic chemical compound which is commonly used in
EPR spectroscopy.
The structural models were visualised using VESTA
software [22,23].
3. Results and discussion
3.1. Mn2+
Manganese is one of the most commonly used para-
magnetic probes for local structure investigations via EPR
spectroscopy. The characteristic Mn2+ EPR spectrum aris-
es from the hyperfine structure (HFS) interaction between
the d5 shell electron cloud effective spin S = 5/2 and 100%
abundant 55Mn isotope nuclear spin I = 5/2. The resonance
positions in single crystals are also strongly dependent on
the Mn2+ centre symmetry determined by the surrounding
ligand field. Thus, the effective spin-Hamiltonian (SH) is:
q q
k k k
k q
H gBS f b O ASI= β + +∑∑ (1)
where β is the Bohr magneton; g — the g-factor; B — the
applied magnetic field; fk — numerical constants; bk
q —
zero field splitting (ZFS) parameters depending on the site
symmetry; Ok
q — spin operators and A — the hyperfine
interaction constant.
In vitreous media Mn2+ EPR spectrum consists of a
signature sextet (see Fig. 1) centred at g = 2.0 caused by
the hyperfine interaction, whereas the angularly dependent
ZFS part usually is not resolved. The magnetic field range
of the spectrum is characterized by the magnitude of iso-
tropic hyperfine interaction constant A, and is an indicator
of local chemical environment around the impurity. A
more ionic bonding to the surrounding ligands results in a
larger A value [24].
In InF3 based glass ceramics, heat treatment of the pre-
cursor glass has caused the increase of the signal/noise
ratio of the characteristic sextet indicating localization of a
larger part of Mn2+ ions in highly order sites [12]. In
tellurite borate glass ceramics, local Mn2+ site symmetry
has been monitored from SH parameters as a function of
manganese content in the composition [13]. Oxyfluoride
glass ceramics containing fluorite structure crystallites
(CaF2, SrF2, BaF2) have shown particularly interesting
results — additional superhyperfine structure (SHFS) split-
ting of each spectral line after the precipitation of fluoride
nanocrystals in the glass matrix can be observed [14–17].
Figure 1 shows Mn_C composition glass and the re-
spective glass ceramic obtained after the heat treatment at
(700 ± 10) °C. The superimposed SHFS in the glass ceram-
ic is caused by the interaction between the Mn2+ effective
spin S and the spins of N nearest fluorine nuclei IF = 1/2.
As a result, each HFS line is split into 2NIF + 1 compo-
nents with binomial intensity distribution. Splitting into 9
components in our case means that Mn2+ ions substitute
Ca2+ ions in CaF2 nanocrystals and are surrounded by 8
equidistant fluorine nuclei. The results obtained here are
consistent with Refs. 14–17.
EPR studies of manganese paramagnetic probes in glass
ceramics thus yields information not only about the for-
mation of crystallites in the glass matrix, but also helps to
assess the first coordination sphere around the dopant ions
in the crystalline phase.
3.2. Cu2+
Copper ions are commonly used spin probes for local
structure investigations in vitreous media [25–29]. For the
interpretation of characteristic Cu2+ spectrum (see Fig. 2),
an axial SH should be applied:
( )
( )
||
|| .
z z x x y y
z z x x y y
H g B S g B S B S
A S I A S I S I
⊥
⊥
= β +β + +
+ + +
(2)
The Cu2+ ion has S = 1/2 and I = 3/2 for both isotopes
63Cu and 65Cu and thus a HFS splitting into four resonanc-
es is expected for both parralel and perpendicular compo-
Fig. 1. (Color online) EPR spectra of the manganese doped glass
(1, black) and the glass ceramic (2, red) containing CaF2. Inset
shows the eightfold coordinated Mn2+ site in CaF2 nanocrystals.
450 Low Temperature Physics/Fizika Nizkikh Temperatur, 2018, v. 44, No. 4
Crystalline phase detection in glass ceramics by EPR spectroscopy
nents of the g tensor. Such spectral features are characteris-
tic of Cu2+ ions in distorted octahedral sites elongated
along the z-axis. The SH parameter values indicate the
strength of the surrounding ligand field.
Literature about the incorporation of copper ions in the
crystalline phase of glass ceramics, on the other hand, is
somewhat scarce. Previous study of Cu2+-doped InF3
based glass ceramics has observed a relatively broad
Gaussian line superimposing the glassy spectrum after the
heat treatment of the precursor glass, however, its origin
was related to oxygen/water content in the atmosphere
during the glass preparation [12]. Here Fig. 2 shows the
EPR spectra of Cu_C composition glass and the corre-
sponding glass ceramic heated at (700 ± 10) °C. Spectrum
shape near g = 2.0 has changed, however, the lack of struc-
ture in this resonance prohibits additional information
about the nature of this paramagnetic centre. Nevertheless,
changes in the EPR spectra shape observed after the crea-
tion of crystallites in the glass allows, in principle, to de-
tect the crystalline phase in glass ceramics.
3.3. Gd3+
Most potential applications of glass ceramics revolve
around the luminescence of rare earth ions, therefore, the
local structure of trivalent defects in these systems is of
great interest. Unfortunately, direct observation of most
rare earths is problematic either due to the lack of para-
magnetic ground state or by the necessity of liquid helium
temperatures to observe the spectrum. The unusually long
spin-lattice relaxation time of gadolinium makes it one of
the most useful paramagnetic probes for studying the
“glass → glass ceramic” transition even at room tempera-
ture. The ground state of Gd3+ is an S-state (4f
7; S = 7/2)
and the splitting in external magnetic field is described by:
q q
k k k
k q
H gBS f b O= β +∑∑ . (3)
Gd3+ in disordered media is characterized by the signa-
ture U-type (ubiquitous) spectrum with resonances at
geff = 6.0, 2.8 and 2.0. Coordination with a relatively large
number of ligands at inequivalent distances can be simu-
lated by taking a relatively broad distribution in second-
order ZFS parameters [30,31]. In crystalline media, the
nature of Gd3+ local environment is host sensitive and can
yield valuable information about the material in study [32].
After precipitation of a crystalline phase in the glass ma-
trix, intensive resonances centred at g = 2.0 usually super-
impose the U-type spectrum [12,18]. An example is shown
in Figs. 3 and 4 — Gd_N composition glass and the corre-
sponding glass ceramic containing NaLaF4 nanocrystals.
The XRD spectra clearly show the formation of NaLaF4
nanocrystals in the glass matrix. Meanwhile, the intense
new EPR signal indicates efficient incorporation of triva-
lent rare earth impurities in the crystalline phase of glass
ceramics. For a better understanding of gadolinium centres
in NaLaF4, EPR angular variations in single crystalline
sample should be studied.
In order to extract the most from EPR spectra, an opti-
mal concentration of paramagnetic impurities should be
used. In Fig. 5 glass ceramics containing SrF2 crystalline
phase and Gd3+ ions in different concentrations are com-
pared. The fine structure is best resolved at relatively lower
dopant concentration and is significantly broadened due to
the dipolar interaction between the paramagnetic centres at
higher doping levels. At high concentration, various forms
of composite defects such as gadolinium ion pairs and
clusters may also be present.
Gd3+ in oxyfluoride glass ceramics containing fluorite
structure crystalline phase have been studied recently [19,20].
Main results for compositions containing CaF2, SrF2 and
BaF2 are summarized in Fig. 6. EPR spectrum structure
strongly depends on the local symmetry around Gd3+ im-
purities in these nanocrystals. When trivalent gadolinium
Fig. 2. (Color online) EPR spectra of the copper doped glass and
glass ceramic containing CaF2.
Fig. 3. (Color online) XRD spectra of the gadolinium doped glass
and glass ceramic containing NaLaF4. The blue curve is the calcu-
lated polycrystalline NaLaF4 diffractogram. Peak marked with *
belongs to the NaF crystalline phase.
Low Temperature Physics/Fizika Nizkikh Temperatur, 2018, v. 44, No. 4 451
A. Antuzevics, U. Rogulis, A. Fedotovs, and A.I. Popov
replaces the divalent cation, a charge compensation is nec-
essary. Depending on the compensator orientation in the
lattice, various forms of Gd3+ centres are possible in
fluorite structure crystals — cubic centres when the com-
pensator is located far from the impurity [33], tetragonal
centres where usually an interstitial fluorine anion located
along [100] direction distorts the original cubic configura-
tion [34] and trigonal centres if the charge is compensated
by an additional impurity along the [111] direction [35].
The mentioned Gd3+ symmetries in fluorite type crystals
are illustrated in Fig. 7. When Gd3+ replaces the similarly
sized Ca2+ ions in glass ceramics containing CaF2, the
EPR spectrum is dominated by Gd3+ in local cubic sym-
metry crystal field [19], whereas substitution of signifi-
cantly larger Ba2+ ions in glass ceramics containing BaF2
leads to an EPR signal characterized by SH parameters for
trigonal site symmetry [20].
To summarize, EPR spectral features of Gd3+ ions are
sensitive to the local environment and are effective for de-
tecting the presence of crystalline phase in glass ceramics.
The results obtained from the studies of Gd3+ EPR spectra
could also be used to analyse non-magnetic trivalent rare
earth ions, local structure of which cannot be studied by
magnetic resonance spectroscopy.
3.4. Eu2+
The electron configuration of Eu2+ ground state is the
same as for Gd3+ (4f
7; S = 7/2), however, the EPR spec-
trum is complicated by the HFS interaction with europium
isotopes 151Eu and 153Eu (I = 5/2). As a result, each ZFS
component is further split into two sets of sextets and
SH (1) must be used for interpretation. In glass ceramics
doped with Eu2+, the randomly orientated crystallites are,
therefore, expected to generate much broader lines than
similar systems with Gd3+. EPR studies of europium doped
systems may also be hindered by the presence of stable
non-magnetic Eu3+ ions which are generally more abun-
dant unless special reduction has been carried out during
the sample preparation.
Eu2+ EPR signal has been observed in glass ceramics con-
taining BaBr2. Successful simulation of the spectrum with the
single crystal SH data confirmed that the signal originates
from the BaBr2 crystalline phase of glass ceramics [21].
Europium doped glass ceramics are promising materials
for optical applications and the luminescence properties
have been studied extensively in various systems contain-
ing fluorite type nanocrystals [36–38]. As well-known
from the literature, the broad emission of Eu2+ 5d → 4f
luminescence is sensitive to the local ligand field and, thus,
some EPR data could contribute to a better understanding
of these systems.
A recent study [39], in particular, focuses on monitoring
the valence state of europium ions in different composition
glass ceramics containing SrF2. Sharp lines in the EPR
spectra can be observed after the heat treatment of the pre-
cursor glass at high temperatures, where Eu3+ → Eu2+ re-
duction and incorporation into crystalline phases is efficient,
Fig. 4. (Color online) EPR spectra of the gadolinium doped glass
and glass ceramic containing NaLaF4.
Fig. 5. (Color online) Gd3+ concentration dependance of the EPR
spectra of glasses and glass ceramics containing SrF2.
Fig. 6. (Color online) EPR spectra of glass ceramics containg
CaF2 [19], SrF2 and BaF2 [20] nanocrystals.
452 Low Temperature Physics/Fizika Nizkikh Temperatur, 2018, v. 44, No. 4
Crystalline phase detection in glass ceramics by EPR spectroscopy
whereas Eu2+ ions in the glassy matrix can be detected by
the signature U-type spectrum. Combining the EPR data
with photoluminescence spectra allows a direct attribution of
Eu2+ local structure to particular optical properties.
4. Conclusions
1. d-element (Mn2+, Cu2+) and f-element (Gd3+, Eu2+)
paramagnetic probes are suitable for detecting the incorpora-
tion of activators in the crystalline phase of glass ceramics.
2. Variation of Mn2+ and Cu2+ spectral shapes after the
precipitation of crystalline phases in the glass matrix indi-
cates the change of local environment around the impuri-
ties. Coordination of Mn2+ in nanocrystals can be deter-
mined if the SHFS is resolved in the EPR spectrum.
3. Intensive EPR signal emerges and overlays the glassy
U-type spectrum after the heat treatment of the precursor
glass if Gd3+ ions embed in the crystalline phase. The res-
onance positions depend strongly on the local crystalline
field, therefore, local site symmetry around the impurity
can be determined.
4. Europium ion valence state can be monitored from
EPR spectra measurements. Similarly to Gd3+, Eu2+ ions in
the glass matrix exhibit the signature U-type spectrum and
incorporation into crystalline phases of glass-ceramics can
be determined via additional EPR spectrum fine structure.
Acknowledgements
The authors thank Meldra Kemere and Dr. Edgars Elsts
for sample synthesis and Reinis Ignatans for XRD meas-
urements. Financial support of Latvian-Ukrainian Joint
Research Project No. LV-UA/2016/1 is acknowledged.
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1. Introduction
2. Experimental
3. Results and discussion
3.1. Mn2+
3.2. Cu2+
3.3. Gd3+
3.4. Eu2+
4. Conclusions
Acknowledgements
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