Vladimir I. Korepanov

Pulsed photo- and cathodoluminescence of LiF crystals doped with tungsten oxide

We have studied the spectral and kinetic characteristics of activated photo- and cathodoluminescence of LiF-O and LiF-WO3 crystals in the spectral range of 3.6–1.6 eV using methods of pulsed spectrometry with nanosecond time resolution in the temperature range of 15–300 K and in the range of ionizing radiation dose absorbed by crystals of 102−2 × 103 Gy.

Impurity cathodoluminescence of oxygen-containing LiF crystals

Cathodoluminescence of oxygen-containing LiF crystals (LiF-O, LiF-O,OH, LiF-WO3) is studied by pulsed spectrometry with nanosecond resolution upon excitation of crystals by a single electronbeam pulse at 15 K.

The efficiency of formation of primary radiation defects in LiF and MgF2 crystals

Processes of radiation formation of primary defects—F centers and self-trapped excitons—in lithium and magnesium fluorides, which have crystal lattices of different types and similar widths of the band gap and valence band, have been studied in a wide temperature range (11–500 K). It is shown that, along with qualitative similarity of the regularities of formation of the defects under study, LiF and MgF2 crystals are characterized at low temperatures (11–100 K) by different relationships between the energy dissipation channels for self-trapping electronic excitations and the types of self-trapped excitons arising.

Evaluation of the Effect of LED-Lamp Spectral Content on the Development of Greenhouse Tomato

The article reports the results of the experiment studied the effect of radiation spectral content (considering its equal intensity in terms of photosynthetically active radiation) on the growth and development of Boets greenhouse tomato breed. We have shown that the effective development of model subjects requires the adaptation of radiation spectral content depending on the growth period and type of a plant, unlike the illumination level. The obtained results demonstrate the necessity of creating an adaptive irradiation unit.

Color-tunable photoluminescence and energy transfer of (Tb1−xMnx)3Al2(Al1−xSix)3O12:Ce3+ solid solutions for white light emitting diodes

(Tb1−xMnx)3Al2(Al1−xSix)3O12:Ce3+ solid solution phosphors were synthesized by introducing the isostructural Mn3Al2(SiO4)3 (MAS) into Tb3Al5O12:Ce3+ (TbAG). Under 456 nm excitation, (Tb1−xMnx)3Al2(Al1−xSix)3O12:Ce3+ shows energy transfers (ET) in the host, which can be obtained from the red emission components to enhance color rendering. Moreover, (Tb1−xMnx)3Al2(Al1−xSix)3O12:Ce3+ (x = 0–0.2) exhibits substantial spectral broadening (68 → 86 nm) due to the 5d → 4f transition of Ce3+ and the 4T1 → 6A1 transition of Mn2+. The efficiency of energy transfer (ηT, Ce3+ → Mn2+) gradually increases with increasing Mn2+ content, and the value reach approximately 32% at x = 0.2. Namely, the different characteristics of luminescence evolution based on the effect of structural variation by substituting the (MnSi)6+ pair for the larger (TbAl)6+ pair. Therefore, with structural evolution, the luminescence of the solid solution phosphors could be tuned from yellow to orange-red, tunable by increasing the content of MAS for the applications of white light emitting diodes (wLED).

Photoluminescence of LiF Crystals Doped with Oxygen-Containing Impurities

The aim of this paper is to study the photoluminescence spectra and photoluminescence excitation spectra in LiF-O, LiF-WO3 and LiF-TiO2 crystals at 20-300 K. It is shown that the luminescence centers in LiF-WO3 and LiF-TiO2 crystals are oxygen ions O2- disturbed by defects. Two absorption bands within 6-4.5 eV and two luminescence bands with maxima at 3.1 eV and 2.64 eV correspond to these centers. The absorption and emission spectra of the oxygen center (3.1 eV luminescence band) are close to those for the (O2-- Va) center.

Pulsed Cathodoluminescence of LiF Crystals Doped with W and Ti

The spectra and kinetics of pulsed cathodoluminescence buildup and decay in LiF-TiO2 and LiF-WO3.crystals have been studied in the temperature range of 20–300 K. It is found that all the LiF crystals doped with metal oxides (Fe, Ti, W) have a similar structure of the luminescence centers – oxygen centers excited by impurities in Fe2O3, WO3 and TiO2 complexes. In all types of the crystals, the processes of energy transfer to luminescence centers are similar (buildup stage).

Luminescence of LiF Crystals Doped with Metal Oxide Impurities

The luminescence spectra and luminescence excitation spectra have been investigated in the spectral range of 6.5–4.4 eV. Pulsed cathodoluminescence of LiF-WО3 and LiF-TiО2 crystals has been studied in the temperature range of 20–300 K. All LiF crystals doped with metal oxides are found to have similar luminescent properties and identical structure of the luminescence centers. It is assumed that photon and electron bombardment induces excitation of different types of О2− oxygen centers perturbed by impurities and Fe2О3, WО3 and TiО2 included in the oxygen complexes.

Stability of color centers in LiYF4 crystals at low temperatures

This paper presents the results of examining the stability of induced radiation defects in crystals at 15K. The following regularities have been established. Defects induced at low temperatures in pure and Nd 3+ doped LiYF4 crystals are unstable: upon termination of radiation, even at 15K induced color centers are visibly destructed, exposure to the halogen lamp light increases the destruction speed significantly. Heating crystals up to 80K results in complete destruction of color centers induced at 15К.