We have used optical and EPR spectroscopy to study the mechanisms for color center formation in nanoporous glasses, polymethylmethacrylate, and alcoholic solutions containing ?-diketonate molecules: Cu(hfac) 2 , Ba(hfac) 2 , Pr(hfac) 3 , and Eu(fod) 3 . We have observed and studied the complex structure of the absorption bands in the 300 nm region belonging to the intraligand π − π * transition. Analogous results were obtained when studying the photoluminescence spectra of 5 D 0 → 7 F 0 transitions of Eu 3+ ions and the EPR spectra of Cu 2+ ions in matrices doped with Cu(hfac) 2 . We propose a model according to which for β-diketonate molecules (except for basic diketonates), a hydrolyzed form exists that is formed during synthesis of the polycrystalline powder due to the presence of water molecules. The model allows us to explain the spectral manifestations of β-diketonates in different matrices.
It is shown that electron paramagnetic resonance can be used to study the fine structure of glasses and glass enamel materials as well as to find and identify defects in glass. The spectra of paramagnetic ions (Cu 2+ , V 4+ , Ti 3+ , Mo 5+ Mn 2+ , Fe 3+ ) are discussed. Specific examples of the detection of these ions in sitals, in which they are introduced as surface-active additives or are present as impurities entering the crystallized glass via the raw materials, are examined. It is determined that the most informative ions for studying the structure and phase separation of glass are Cu 2+ and V 4+ . Electron Paramagnetic ResonanceElectron paramagnetic resonance (EPR), discovered experimentally by E. K. Zavoiskii in 1944, is now widely used as a method of investigating different substances and processes in physics, chemistry, biology, geology, medicine, and other areas of science and technology. It should be noted that the EPR phenomenon has also been studied intensively from the theoretical and experimental standpoints. However, as a method of investigating substances or the processes occurring in them its importance is not diminishing but rather increasing because the range of new materials and their applications is expanding.EPR is a spectral method, based on resonance absorption of microwave electromagnetic radiation by paramagnetic particles, whose magnetic moments are tuned in resonance by applying a magnetic field.All substances contain electrons possessing orbital and spin magnetic moments, and one would think that EPR can be observed for all of them. However, the atoms and molecules comprising matter are constructed in such a manner that their filled electronic shells have a zero magnetic moment. EPR is observed only for 1) magnetic centers specially created by high-energy radiation (g-, x-rays, fast neutrons, ions of heavy particles, and others), 2) free radicals, and 3) atoms with initially unfilled inner electronic shells (transition elements (TE) with partially filled 3d-, 4d-, or 5d-shells, rare-earth elements with an unfilled 4f-shell and actinides with an unfilled 5f-shell). Such substances contain centers possessing constant magnetic moments, randomly oriented relative to one another in the absence of an external magnetic field. In accordance with Boltzmann's law most magnetic moments are oriented along the field.The energy of particles with a magnetic moment m directed parallel to an external magnetic field (lower energy level) is less than the energy of particles with m oriented opposite to the field (upper energy level). When a high-frequency electromagnetic field is applied absorption of electromagnetic energy equal to the energy difference DE between the upper and lower energy levels (in the case of a two-level system) occurs and is accompanied by re-orientation of the magnetic moment of the particle (resonance transition from the lower to the upper level). The resonance condition has the formwhere g is a spectroscopic splitting factor dependent on the nature of the magnetic moment and i...
Glasses in the system Al 2 O 3 -P 2 O 5 -SiO 2 , which are suitable for the green light filters in traffic signal lights, were investigated. The glasses were required to satisfy the following requirements: transmission band maximum at l max = 500 nm high heat-resistance, and low CLTE -(41 -49)´10 -7 K -1 . Transition elements served as colorants; they were introduced into the batch as the oxides TiO 2 , V 2 O 5 , CuO, and MoO 3 in amounts 1 wt.%, as well as their pairs in different combinations. The EPR and optical spectra were investigated. It was shown that glass with the composition (wt.%) 55 P 2 O 5 , 17.1 Al 2 O 3 , 20 SiO 2 , 1.5 La 2 O 3 , 2 ZrO 2 , 2.5 B 2 O 3 , 1.5 MoO 3 , and 0.5 CuO can be recommended for use as heat-resistant green light filters.Colored light filters are used for signal lights in aviation, railroad, and sea transport. The glasses used for light filters must possess definite characteristics (color, thermal, mechanical, and others) for reliable recognition of the signal color at a considerable distance under different operating conditions (elevated temperature, velocity of the object, atmospheric precipitation, and others).Glasses which can be used to manufacture green signal light filters were studied in the present work. Glasses to be used for such applications have been developed and used in different organizations, including with the participation of the present authors (for example, [1,2]). Such glass must be practicable, have a low linear thermal expansion coefficient (CLTE) in the range (35 -50)´10 -7 K -1 , high heat-resistance (no lower than 300°C) and light transmission at least 20% near maximum transmission at 500 nm (bluish-green color).The glasses are usually colored by transition elements (TE). Theoretically and experimentally, the electronic absorption spectra of TE due to transitions between sublevels of the d-shells (d -d transitions), which are characterized by small extinction coefficients, lie in the visible, near-UV, and IR frequencies of electromagnetic radiation. The transitions are forbidden by selection rules with respect to the orbital quantum number. In the absence of a center of symmetry (octahedral environment of the TE) the d shells can mix with the p shell as a result of thermal vibrations, making the transitions allowed though weak. In tetrahedral coordination, when a center of symmetry exists, the absorption bands become stronger.The valence and coordination state of TE and the position and shift of the electronic absorption bands depend on the optical basicity of the glass, which essentially characterizes the capability of oxygen to impart negative charge to a transition element. The basicity of the glasses depends on their properties and is highest in alkali-containing glass. For example, the optical basicity L, which can be calculated using the relations presented in [3], equals 0.65 in glass with molar content 40 Na 2 O and 60 SiO 2 , L = 0.46 with 30 Al 2 O 3 and 70 P 2 O 5 , and L = 0.43 with 33 SiO 2 and 67 P 2 O 5 .In the present work we studied ...
The EPR and optical absorption spectra of V 4+ ions and their relation with the structural features of glasses in the system La 2 O 3 -Al 2 O 3 -SiO 2 are investigated. Three characteristic ranges of the V 4+ EPR parameters are established: I) A y » 167´10 -4 cm -1 , g y = 1.937 -1.938; II) A y » (163 -164)´10 -4 cm -1 , g y = 1.939 -1.940; III) A y » (156 -159)´10 -4 cm -1 , g y = 1.945. It is shown that in the region I with low La 2 O 3 content the lanthanum is predominately a modifying ion, and in glass with a high La 2 O 3 concentration lanthanum gradually occupies a site in the glass, bonding silicon-oxygen and aluminum-oxygen tetrahedra, i.e., it becomes a glass former even though its ionic radius is large. Region III glasses with high La 2 O 3 content possess a high softening temperature and anomalously high thermal conductivity (about 12.6 W/(m × K)).Key words: electron paramagnetic resonance (EPR), optical spectra, lanthanum-aluminosilicate glass, vanadium (IV) ions.In the present work we studied the system La 2 O 3 -Al 2 O 3 -SiO 2 in connection with the development of thermally stable glasses with low CLTEs (35 -50)´10 -7 K -1 and a prescribed narrow transmission band in the green part of the spectrum (peaking near 500 nm) for signal lights used in aircraft.Some properties of the glasses in this system have been investigated in [1]. These glasses are characterized by a high refractive index (up to 1.767) and high density (up to 4.17 g/cm 3 ). The main distinguishing feature of these glasses is their high deformation-onset temperature (855 -940°C) with CLTE (33.7 -64.0)´10 -7 K -1 . As compared with other commercial tungsten-group glasses with CLTE about 40´10 -7 K -1 , the deformation-onset temperature of lanthanum-aluminosilicate glasses is shifted by 80 -100°C toward high temperatures, i.e., they can be used for work at higher temperatures (750 -800°C). Possessing anomalously high thermal conductivity (about 12.6 W/(m × K)), these glasses find applications as integrated-circuit boards with fast heat removal and as laser materials.The investigation of the system La 2 O 3 -Al 2 O 3 -SiO 2 is also of fundamental value. The glass-formation region in this system at the maximum synthesis temperature 1600°C was determined in [2]. The region of glass-formation becomes wider when La 2 O 3 -Al 2 O 3 -SiO 2 glasses are synthesized by the method of microwave fusion in a sold container at approximate temperature 2000°C in air [1]. The products of crystallization of glasses in this system have been studied in [3 -5] in different sections of the glass-formation region. It was determined that for high La 2 O 3 content lanthanum disilicate forms and for comparatively low content lanthanum-aluminosilicate La 4 Al 4 Si 5 O 22 forms.It has been suggested in [1] on the basis of an analysis of the properties of La 2 O 3 -Al 2 O 3 -SiO 2 glasses with different La 2 O 3 : Al 2 O 3 ratio but constant SiO 2 content that the La 3+ ions in the structural network of glasses in this system can occupy two non-equivalent positions...
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