Ceramic samples of Y
3
MgGa
3
SiO
12
, Y
3
MgGa
2
AlSiO
12
, and Y
3
MgGaAl
2
SiO
12
multicomponent garnets doped with 0.2 at % Cr
3+
have been obtained by high-temperature solid-state synthesis. In ...the luminescence spectra of the synthesized garnet samples, overlapping broadband luminescence is observed in the far red spectral region caused by the
4
T
2
→
4
A
2
transition in Cr
3+
ions, and a narrow band is observed in the range of 690–700 nm, corresponding to the zero-phonon line of the
2
Е →
4
A
2
transition in Cr
3+
. The narrow-band and broad-band parts of the spectra are attributed to radiation from two different types of chromium centers, which are in octahedral coordination with different distortion degrees and strength of the crystal field. This results from the presence of two ions at the octahedral position of these garnets, which differ significantly in crystal chemical properties, namely, Mg
2+
and Ga
3+
(Al
3+
). The studied phosphors, which have broadband luminescence in the phytoactive far red region of the spectrum, have the potential for use in greenhouse LED lamps.
—
Ceramic LiAl
5
O
8
lithium aluminate spinel materials doped with trivalent chromium ions have been prepared by high-temperature solid-state synthesis. The intensity, spectral shift, and width of ...two zero-phonon luminescence lines (
R
lines) due to transitions from the
2
E
excited state to the
4
A
2
ground state of Cr
3+
ions have been measured as functions of temperature in the range 80–295 K. Analysis of luminescence and luminescence excitation spectra of the ceramics points to severe local lattice distortion around the Cr
3+
ions, which shows up, in particular, as large inhomogeneous broadening of the zero-phonon Cr
3+
luminescence lines. The temperature dependences of the relative intensity, spectral shift, and width of the two zero-phonon lines can be sufficiently well described in terms of existing models for optical centers in crystals. The feasibility of using these temperature dependences for noncontact luminescence thermometry is assessed. Analysis of the data obtained in this study provides no way to uniquely identify the observed zero-phonon lines as due to transitions from two sublevels of the
2
E
state of a single type of chromium center (that is, as
R
1
and
R
2
lines) or transitions of two inequivalent chromium centers coupled by nonresonant energy transfer.
Ceramic lithium aluminum spinels doped with manganese ions have been synthesized by a high-temperature solid-state reaction. Samples fabricated by annealing at 1000, 1100, 1200, or 1300°C in air for ...4 h have been identified as LiAl
5
O
8
, which is cubic spinel belonging to the space group
P
4
1
32. After annealing at 1000–1200°C, samples with the lattice parameter
a
= 7.923–7.925 Å show intense red luminescence of Mn
4+
ions, which has a narrow luminescence band with a maximum at 662 nm. The excess charge of Mn
4+
ions replacing Al
3+
ions in the octahedral sites of the LiAl
5
O
8
lattice is compensated for by an excess amount of lithium ions (compared to the stoichiometry) substituting for Al
3+
ions adjacent to Mn
4+
. However, annealing at a higher temperature (1300°C) leads to the almost complete disappearance of the Mn
4+
luminescence at 662 nm, although X-ray powder diffraction shows that the crystal structure of these ceramics remains the same one (space group
P
4
1
32), but the lattice parameter
a
becomes 7.908 Å, which exactly corresponds to the lattice parameter of the LiAl
5
O
8
single crystal. It is suggested that ceramics with a larger lattice parameter obtained at lower temperatures are solid solutions in which some of the Al
3+
ions are replaced by larger Li
+
ions. Such solid solutions are not stable and lose Li
+
ions upon annealing at a high temperature to convert to the stoichiometric compound LiAl
5
O
8
. In stoichiometric LiAl
5
O
8
, Mn
4+
ions cannot be stabilized in the octahedral sites due to the lack of a charge compensation mechanism, and there is no red luminescence of Mn
4+
ions in such samples.
—
Using content analysis and the Python programming environment, we have found a number of general relationships determining the thermal properties of fluoride and modified fluoride glasses. Their ...compositions have been classified according to their glass transition temperature (
T
g
) and the difference between their crystallization onset temperature (
T
x
) and glass transition temperature:
T
x
–
T
g
. The use of Kauzmann’s rule for fluoride glasses, unmodified and modified with other halogens, has been shown to be more reliable if the
T
g
/
T
m
ratio is used, compared to the
T
g
/
T
l
ratio. We have qualitatively assessed how anion modification influences characteristic temperatures (glass transition temperature
T
g
, crystallization onset temperature
T
x
, crystallization peak temperature
T
c
, melting onset temperature
T
m
, and liquidus temperature
T
l
) and crystallization stability criteria (Hruby criterion
K
, Saad–Poulain criterion
S
, reduced thermal stability interval
H
, thermal stability interval
T
x
–
T
g
, and reduced glass transition temperatures
T
g
/
T
m
and
T
g
/
T
l
).
A method to synthesize spinel (MgAl
2
O
4
)–based compounds doped with magnesium ions was developed, which makes it possible to create red-emitting phosphors (band peak at 651 nm) or green-emitting ...phosphors (band peak at 525 nm) due to the luminescence of Mn
4+
or Mn
2+
, respectively, and also phosphors that have both (red and green) emission bands. Both types of luminescence exhibit quite high thermal stability; particularly, the green luminescence does. Namely, the temperature at which the luminescence intensity halves in comparison with the maximum intensity is
T
0.5
= 448 and 737 K for the red (Mn
4+
) and green (Mn
2+
) luminescence, respectively. On the other hand, for the phosphors that have both emission bands, the temperature dependences of the intensities of the red and green luminescence more closely resemble each other because of the energy transfer from Mn
4+
ions to Mn
2+
ions. Both emission bands are efficiently excited in the blue spectral region, which enables the use of the conventional three-color RGB (red–green–blue) method to create LED white-light sources based on a combination of a blue light-emitting diode and a phosphor containing manganese ions with an optimally chosen ratio between the intensities of the green and red emission bands.
A process for the growth of VSe
2
and VTe
2
single crystals using VCl
3
as a transport agent is proposed and experimentally demonstrated. X-ray diffractometry and Laue X-ray photography results ...indicate that the crystals thus grown are identical in properties to chalcogenide crystals grown using I
2
as a transport agent. The mechanism of chemical vapor transport is discussed and the process conditions are optimized.
Fluorozirconate glasses, including those with partial replacement of fluorine by chlorine in the composition, doped with MnO
2
and K
2
MnF
6
, have been synthesized, and their optical absorption and ...EPR have been studied. The EPR data demonstrate the absence of isolated Mn
4+
ions in the samples. The absorption spectra arise from Mn
2+
and Mn
3+
ions, which are formed because of the reduction of Mn
4+
ions introduced with MnO
2
and K
2
MnF
6
activators. It has been found that the replacement of fluorine by chlorine is accompanied by an increase in the relative concentration of Mn
3+
in glass.
—
This paper presents results on the physicochemical properties of arsenic-containing substances—lewisite detoxification (destruction) products. Major attention is paid to the properties of ...hydrolytic sodium arsenite, a promising alternative industrial raw material for the production of high-purity arsenic and its compounds. Data are presented on the macro- and microcompositions of raw materials and temperature-dependent density and saturated vapor pressure of H
3
AsO
4
solutions. The experimental data can be used in processing unconventional raw materials into extrapure arsenic-containing compounds.
Judd–Ofelt(J–O) analysis of Er3+:K2YF5 crystals has been performed to evaluate the spontaneous emission probabilities, radiative lifetimes and luminescence branching ratios for Er3+ions from the ...viewpoint of developing novel laser materials. The derived J–O parameters are Ω2=1.216, Ω4=0.647 and Ω6=0.459×10−20cm2 for a K2Y0.9Er0.1F5 crystal. Radiative lifetimes of the 4I13/2and 4I11/2 states are as long as 14.9ms and 17.4ms, respectively. Stimulated-emission cross-sections spectra are presented for the 4S3/2→4I15/2, 4I13/2→4I15/2 and 4I11/2→4I13/2 transitions. The maximum σSE values are 1.5×10−20cm2 at 558nm, 0.72×10−20cm2 at 1531nm and 0.40×10−20cm2 at 2705nm,respectively. Non-radiative relaxation rates have been determined for the excited-states of Er3+ions in K2YF5. It is assumed that Er3+:K2YF5 crystals are promising for green up-conversion lasers.
—
This paper describes a detailed study aimed at developing technological principles of the preparation of 99.99995%-pure Cd, Zn, and Te by crystallization purification methods. We have analyzed the ...thermophysical properties of Cd, Zn, Te, and structural materials of the equipment involved; substantiated the choice of graphite as a crucible material; and determined its engineering features. We have studied impurity distributions in Cd, Zn, and Te in crystallization processes and determined effective performance parameters of the materials refining process in horizontal directional solidification and zone melting steps. The results have allowed us to obtain 99.99995 to 99.99999%-pure Cd, Zn, and Te in terms of 30 major impurities, with a maximum product yield of up to 85%.
