•Optical properties of YAG crystals grown under different conditions are compared.•Carbon admixture with the concentration up to 0.01 wt% in YAGMo crystals grown under reducing conditions is found.•A ...procedure of YAGMo irreversible bleaching in the 200–1100 nm range by heat treatment is proposed.
Optical properties of YAG crystals grown and annealed under different atmosphere conditions have been compared. Simultaneously we have registered the surface composition of crystals and content of basic admixtures in the crystals grown under the reducing conditions. Unlike YAG grown under weakly oxidizing conditions in Ir crucibles and bleached under oxidizing annealing, YAGMo crystals grown in Mo crucibles under reducing Ar + CO atmosphere can be bleached by both oxidizing and reducing thermal annealing. The bleaching of YAGMo is not reversed by further annealing under any available conditions. Mechanisms of this phenomenon have been discussed, including a possible role of admixtures in elimination of color centers in YAG grown under the reducing conditions.
Optical absorption, luminescence spectra, scintillation decay curves, and scintillation light yield were measured in a series of undoped yttrium-aluminum garnet (YAG) crystals of different origins. ...This paper reveals a correlation between luminescent properties and scintillation efficiency of undoped YAG crystals. All the samples were separated into three groups, Type I, Type II, and Type III, based on their optical properties and scintillation efficiency. The intrinsic ultraviolet luminescence band peaking around 300 nm is found in the samples with high scintillation yield (Type I). Luminescence intensity of this band depends on the crystal purity and on the stoichiometry of the garnets. The UV emission may be related to e-h recombination in vicinity of vacancies. The garnets of Type II contain more impurities which quench the 300-nm emission. The samples of Type III do not exhibit any significant radioluminescence. Light yield of the finest undoped YAG samples in the series, Type I, is similar to the yield of Ce-doped YAG. This Type of crystals can potentially be used in scintillation detectors.
Switched reluctance motors (SMRs) are competitors of traditional ones in electric vehicles due to their high specific performance and the absence of permanent magnets and windings in the rotor ...design, which increases reliability and reduces production costs. Due to the pronounced nonlinearity of their magnetic characteristics and discreteness in control, SRMs are characterized by significant torque ripples, noise, and vibrations, to suppress which it is advisable to use direct instantaneous torque control (DITC), which is widely used in traditional electric drives. However, SRMs differ from traditional motors, so known technical solutions cannot be applied to them. Simulation modeling is a convenient and universal tool for research and development of methods and algorithms for SRM control, and the MATLAB/Simulink environment makes it possible to successfully implement them. The article considers two of the best-known and fundamentally different DITC options with respect to a four-phase SRM. Their shortcomings are substantiated and illustrated, and a new DITC option is proposed that is most suitable for controlling an SRM as part of a traction electric drive of electric vehicles.
► The optical and luminescence properties of CsI:Eu crystals has been studied. ► Intense low temperature luminescence band at 441nm in CsI:Eu is observed. ► The temperature evolution of emission ...bands shows the change of the main mechanism. ► Excitonic mechanism plays the main role in energy transfer process in CsI:Eu.
The work is aimed to research of CsI:Eu single crystals’ luminescence at different excitations in the wide temperature range (from 8 to 300K) and admixture concentration from 10−4% up to 10−1% of Eu2+ ions. This study was directed to separation of different luminescence mechanisms and luminescence quenching explore. It is found that due to the temperature quenching the room temperature yield is decreased in order of magnitude even for heavy Eu doped CsI crystals. Intense low temperature luminescence band at 441–448nm connected with Eu2+ 4f6 5d→4f7 radiative transition is observed. The results obtained show that the excitonic mechanism plays the main role in energy transfer process to Eu2+ ions and this is the reason for relatively low light yield of this emission at RT. The nature of the additional emission bands (410, 450, 480 and 500nm) are apparently caused by the significant non-isomorphism of cations and/or by the presence of oxygen-containing admixtures.
The influence of different activator impurities on the scintillation yield of alkali halides has been investigated as a function of temperature. Luminescence spectra of pure and activated CsI and NaI ...scintillation crystals were measured under X‐ray and VUV excitation at temperatures from 10 to 300 K. In indium‐ and thallium‐doped crystals activator centers can capture electrons. Along with self‐trapping of holes at low temperatures, electron capture by the dopant results in energy storage. This leads to a significant decrease of luminescence yield. In Eu‐doped NaI and CsI crystals activator centers capture a hole first. In this way, at low temperatures electrons recombine either with self‐trapped holes (yielding STE emission), or with holes trapped by the activator (giving rise to Eu emission band). No energy loss at low temperature is evident in CsI:Eu and NaI:Eu crystals.
•The optical and luminescence properties of CsI:Eu crystals has been studied.•Several types of activator centers were revealed.•The total content of impurities in the grown crystal CsI:Eu can reach ...∼10−3mass%.•There are four main types of luminescence centers in CsI:Eu crystals.
Absorption, excitation and luminescence spectra of pure and Eu doped CsI crystals were studied depending on the activator content, excitation energy, heat treatment and X-ray irradiation. Several types of Eu2+ related centers were found. It is shown that complex centers are stable at room temperature but their structure and concentration changes at heat treatment and under irradiation. The increased content of oxygen-containing radicals was determined by IR spectroscopy in Eu-containing crystals as opposed to pure one. It is supposed that some of emission centers in CsI:Eu are caused by the presence of intrinsic (vacancy type) and extrinsic (oxygen or hydroxyl ions) defects located in the nearest environment of Eu2+ ions.
Results of spectrographic study of zonal soils with different erosion degree on the territory of the Chuvash Republic are given. In the points of spectrographic research, the soil specimens were ...taken and agrochemically tested. Changes in received spectrograms were analyzed in soils subtypes context with subsequent comparison with agrochemical indicators. The obtained data will help to develop new rapid methods for determining soil fertility parameters for agricultural lands based on spectroscopic physical principles.
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