ISSN 1070-4272, Russian Journal of Applied Chemistry, 2014, Vol. 87, No. 7, pp. 853−860. © Pleiades Publishing, Ltd., 2014.
Original Russian Text © F.F. Grekov, B.V. Chernovets, 2014, published in Zhurnal Prikladnoi Khimii, 2014, Vol. 87, No. 7, pp. 858−865.
INORGANIC SYNTHESIS AND INDUSTRIAL
Synthesis of α-Eucryptite by the Sol-Gel Method
F. F. Grekov and B. V. Chernovets
St. Petersburg State Polytechnical University, ul. Politekhnicheskaya 29, St. Petersburg, 195251 Russia
Received May 27, 2014
Abstract—New method is reported for synthesis of α-eucryptite LiAlSiO
whose framwork structure has voids
that enable its doping with lanthanides. The optical parameters of this orthosilicate and results of introduction of
europium ions into its composition to create a phosphor were studied.
One main development areas of modern lighting engi-
neering is to create high-efﬁ ciency semiconductor light-
emitting diodes (LEDs). The most widely used LEDs are
those based on gallium nitride. In these devices, photons
with comparatively high energies, emitted by a crystal,
are converted to light perceived as “white” in the layer
of a phosphor composite contained in the LED structure.
As a rule, the phosphors used in nitride LEDs include
lanthanide atoms as active centers because the electronic
structure of 4f-elements provides the optimal relationships
between the excitation and emission spectra for this kind
of light sources and a high conversion efﬁ ciency.
In addition to the conventional phosphor based on
yttrium-aluminum garnet doped with cerium , re-
searchers’ attention is attracted by variable-composition
phases in the Si–Al–O–N system, “sialons,” doped with
divalent europium and a new class of inorganic phos-
phors, nitride phosphors .
The framwork structure of α-sialon, a derivative of
, is remarkable in that it contains large
voids framed by 9 anions, which correspond in shape to
a tri-face-centered trigonal prism. These voids serve as
natural positions for activating lanthanide atoms because
just this coordination is observed in most of oxygen com-
pounds of lanthanides . Sialon phosphors are rather
effective converters of the blue emission of LEDs [4, 5].
The matrix based on phenacite itself has the same
structural features, but is unpromising for mass-applica-
tion devices for ecological reasons. At the same time, an
orthosilicate of similar structure, α-eucryptite LiAlSiO
is known as a luminescent mineral . This silicate can
be regarded as a product of a heterovalent substitution of
beryllium atoms in phenacite with aluminum and lithium
atoms of nearly the same mass and electronegativity,
which simultaneously juxtaposes the mineral with sialons.
Under ordinary pressures, eucryptite exists in two
modiﬁ cations. The high-temperature β-modiﬁ cation has
been well studied because of being regarded as a prom-
ising ionic conductor and the main component of glass-
ceramics with zero thermal expansion coefﬁ cient. At the
same time, the low-temperature synthetic α-eucryptite
has been little studied. All methods for synthesis of
eucryptite, based on high-intensity thermal activation of
precursors, yield the β-modiﬁ cation. Only two examples
of successful syntheses of α-modiﬁ cation are known, by
the hydrothermal method in both cases [7, 8].
The goal of the present study was to develop
a procedure for synthesis of α-eucryptite by the sol-gel
method and to determine whether a new phosphor can be
in principle created on the basis of a synthetic eucryptite
matrix upon introduction of europium atoms into its
The synthesis was carried out from lithium and alumi-
num salts, with tetraethoxysilane (TEOS) as the source