Mechanism of photoluminescence excitation of Mn<Superscript>2+</Superscript> ions in ZnS crystals

The mechanisms of photoluminescence excitation of Mn²⁺ ions in ZnS crystals have been investigated on the basis of complex analysis of the temperature dependences of the photoluminescence and photoluminescence-excitation spectra of ZnS:Mn crystals. The activation energy of a manganese luminescence center was estimated at E_a = 0.17 ± 0.05 eV. It is shown that E_a represents an energy band with a width ΔE_a = 0.1 eV, within which a manganese luminescence center can experience radiationless recombination. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 6, pp. 788–793, November–December, 2005.     

Time and temperature dependent breakdown characteristics of ZnS:Mn films obtained by rf-magnetron sputtering

Breakdown delay times (t_del) for films of managanese-doped zinc sulfide (ZnS:Mn) were measured in the range 10^–6–10^–1 s. The maximum value was t_del=10^–3–10^–2 s. The electrical strength (E_br) was found to increase as the voltage pulse duration was reduced, the more so the thinner the ZnS:Mn film. The temperature dependence of E_br exhibited a weak reduction in E_br as the temperature was raised to roughly 80°C and a sharp reduction in E_br for T>130°C. A maximum in E_br was observed at T130°C which is presumably explained by a structural modification of the ZnS:Mn film. The experimental results obtained are explained in terms of a combined electronic and thermal breakdown mechanism.State Academy of Control Systems and Radioelectronics, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 3–6, April, 1994.     

Electrical breakdown in ZnS:Mn films grown by rf-magnetron sputtering

We have studied the electrical breakdown field strength E_br of ZnS films doped with Mn(ZnS:Mn), produced by rf magnetron sputtering, as a function of film thickness d in the system Al-ZnS:Mn-Al. Electron-microscope studies have shown that breakdown is initiated under inhomogeneous field conditions imposed both by the roughness of the aluminum electrode and by the polycrystallinity of the ZnS:Mn film. An observed increase in E_br as d is reduced below 0.7 µm, with no polarity effect in breakdown under dc field conditions, is explained in terms of an electron-thermal breakdown model.Institute for Automation and Radio Electronics, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 41–44, March, 1993.     

Luminescence of CsBr:Eu films grown by liquid-phase epitaxy

By liquid-phase epitaxy from an aqueous alcoholic solution, we have obtained films of the well-known storage phospor CsBr:Eu, and we have studied their cathodoluminescence and photoluminescence (PL) spectra compared with the undoped CsBr films. We have established that the structure of the photoluminescence centers of the CsBr:Eu films when excited by laser radiation in the absorption band of the Eu²⁺ ions (λ = 337 nm) includes Eu²⁺-V_Cs isolated dipole centers and CsEuBr₃ aggregate centers, and also luminescence centers based on inclusions of hydroxyl group OH⁻ with the corresponding emission bands in the 440 nm, 520 nm, and 600 nm regions. We have studied the dependence of the spectra and the intensity of the photoluminescence for CsBr:Eu films on annealing temperature in air at 423–483 K, compared with analogous dependences for CsBr:Eu single crystals obtained from the melt. We have shown that annealing the films at T = 423–463 K leads to rapid formation of CsEuBr3 aggregate luminescence centers, while for T > 473 K thermal degradation of these centers occurs. We conclude that the observed differences between the photoluminescence spectra of CsBr:Eu films and CsBr:Eu single crystals may be due to additional doping of the films with OH⁻ ions. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 2, pp. 191–194, March–April, 2006.     

Effect of magnetic pulsed field on luminescence of zinc sulfide doped with CuCl,In, and MnS

The effect of a magnetic pulsed field (MPF) of induction B = 1 T on photoluminescence, electroluminescence, and luminescence excitation spectra of powdered ZnS doped with CuCl, In, and MnS is investigated. It is shown that MPF treatment of these materials changes the photoluminescence spectra only in the case of luminophor ZnS:In whereas only the luminescence excitation spectra change for ZnS:CuCl and ZnS:Mn. __________ Translated from Zhurnal Prikladnoi Spektroskopii Vol. 74, No. 3, pp. 367–372, May–June, 2007.     

Influence of radiation on thin ZnS-Tb films

Changes in thin zinc-sulfide films under the action of the γ-radiation of Co⁶⁰ are studied by investigating electroluminescence spectra of terbium embedded in these films as a luminescent probe. It is shown that changes in the relation of the intensities of bands, a decrease in their halfwidth and the background component, and simplification of the spectrum are observed in a short-wave region of the Tb radiation spectrum that corresponds to⁵D₃→⁷F_j transitions. The same modification of the radiation spectrum is characteristic of ZnS films whose crystalline structure is ordered in the course of thermal annealing at a temperature of 350°C. Based on the analysis of the data obtained it is inferred that irradiating the ZnS films with small radiation doses of 10⁴–10⁵ rad leads to the ordering of their crystalline structure due to the elimination of one of the types of structural defects. Institute of Physics of Semiconductors, National Academy of Sciences of Ukraine, 45, Nauka Ave., Kiev-28, 252650. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 3, pp. 338–341, May–June, 1997.     

D.C. conductivity of transparent conductive ZnO:Al films in the temperature range 80–360 K

An experimental study of the temperature dependence of the d.c. conductivity σ as a function of temperature T in the range from 80–360 K on nanocrystalline ZnO:Al films (Al³⁺ 2%) of thickness 500 nm prepared on glass microscope slides by a dip — coating method is presented. The electrical conductivity σ, which at room temperature varied between 0.1 to 2.7 S/cm, increased almost linearly with T for all the samples. Measurements of the Hall coefficient at room temperature and in a magnetic field of 1.2 T, gave R_H=0.53 cm³C⁻¹, from which a carrier concentration of n=1.18×10¹⁹ cm⁻³ and a carrier mobility of μ=1.40 cm²/Vs were deduced. Paper presented at the Patras Conference on Solid State Ionics — Transport Properties, Patras, Greece, Sept. 14–18, 2004.     

Diffusional relaxation in ZnS after thermal doping at 800°C

Photoluminescence spectra of powdered ZnS thermally doped with MnS are studied. Correlations are demonstrated between variations in the luminescence characteristics of ZnS:Mn, on one hand, and some features of radiation center formation and the diffusion of Mn in ZnS after processing, on the other. It is found that after manganese doping at a temperature (T = 800°C) lower than the phase transition temperature of ZnS, relaxation processes owing to diffusion of Mn in ZnS take place in the material over times as long as 6.10³ h. It is shown that 6.10³ h after doping the α-MnS phase is essentially completely dissolved in the volume of the ZnS. Diffusion of Mn in powdered ZnS is found to occur via several channels, rapid diffusion along interior boundaries and slow diffusion via interstitial space, which indicates the existence of different activation energies for diffusion of Mn depending on its localization within the ZnS lattice.     

Temperature dependence of the bandgap width in FeIn2Se4 single crystals

We have used the Bridgman method to grow single crystals of the ternary compound FeIn₂Se₄ and we have determined their composition and structure. We measured the transmission spectra in the intrinsic absorption edge region in the temperature range 20–300 K. From the transmission spectra, we determined the bandgap width and plotted its temperature dependence. We show that the E_g(T) dependence has a shape typical for semiconductor compounds.     

Excitation spectra and structure of luminescence centers of manganese ions in single crystals of zinc sulfide

We investigate the photoluminescence excitation spectra in ZnS:Mn single crystals at room temperature and at the temperature of liquid nitrogen with a different concentration of Mn²⁺ ions. The strongest bands peaking at 557, 578, 600, and 637 nm are associated with a different position of the Mn ion in the lattice of the crystals under investigation. The difference obtained in the excitation spectra can be explained by the resonance transfer of energy between the Mn ions. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 2, pp. 208–210, March–April, 2000.     

Nuclear orientation study of54Mn impurity in Pt100-x Fe x alloy

The low temperature nuclear orientation of⁵⁴Mn in Pt_99.95Fe_0.05, Pt_99.9Fe_0.1, Pt₉₉Fe₁ and Pt₈₈Fe₁₂ has been studied in the temperature range 12–50 mK and in the external magnetic field range 0–1.2 T. The strong temperature and external magnetic field dependence of the effective fieldB _eff on⁵⁴Mn has been observed even in the range where the host itself is magnetically saturated. This behaviour is interpreted by noncollinearity of the Mn magnetic moments with respect to the macroscopic magnetisation direction.     

Nuclear orientation study of low temperature magnetization of54Mn impurity in ferromagnetic PtFe alloys

Low-temperature nuclear orientation of⁵⁴Mn in ferromagnetic Pt₉₅Fe₅ and Pt₉₀Fe₁₀ hosts has been investigated in 12–50 mK temperature range at external magnetic fields up to 1.2 T. Temperature dependence of the effective magnetic field B_eff on Mn has been observed and interpreted as an effect of misalignment of Mn magnetic moments with respect to the macroscopic magnetization direction at host magnetic saturation.     

Low temperature improvement method on characteristics of Ba(Zr0.1Ti0.9)O3 thin films deposited on indium tin oxide/glass substrates

To improve the electrical properties of as-deposited BZ1T9 ferroelectric thin films, the supercritical carbon dioxide fluid (SCF) process were used by a low temperature treatment. In this study, the BZ1T9 ferroelectric thin films were post-treated by SCF process which mixed with propyl alcohol and pure H₂O. After SCF process treatment, the remnant polarization increased in hysteresis curves, and the passivation of oxygen vacancy and defect in leakage current density curves were found. Additionally, the improvement qualities of as-deposited BZ1T9 thin films after SCF process treatment were carried out XPS, C–V, and J–E measurements.     

Intraband luminescence spectra of insulators and semiconductors excited by pulsed electron beams or electric fields

The features of the intraband luminescence spectrum of wide-gap insulators (KI, KBr, CsCl, etc.) and semiconductors (GaP, CdS, α-SiC, and ZnS) are studied in the temperature interval 80–760 K. The spectra of the intraband luminescence are compared with the spectra of the pre-breakdown electroluminescence of GaP and α-SiC surface-barrier diode structures and of a ZnS thin-film electroluminescence indicator. In alkali halide crystals the short-wavelength boundary hν _m of the intraband luminescence is less than the band gap E _g and is governed by complex excitonic processes. In semiconductors with indirect transitions hν _m>E _g. The differences in the spectra of the intraband luminescence and the intraband pre-breakdown electroluminescence can be explained by differences in the distributions of the hot charge carriers over levels of the allowed bands and in the maximum energies of the carriers involved in the formation of the spectra. Fiz. Tverd. Tela (St. Petersburg) 39, 613–617 (April 1997)     

Mechanooptical investigations of polyimide films exposed to electrons,mechanical loads,and temperatures

Joint effect of high-energy electrons, mechanical loads, and temperature on polyimide films of thicknesses in the range 30–130 μm is investigated. The films were preliminary irradiated by electrons in air using an éLU-6 linear accelerator with energy of 2 MeV and doses D = 1, 5, 10, 20, 30, 40, and 100 MGy and then subjected to uniaxial mechanical tension at temperatures (T) from 293 to 593 K. It is established that at T = 293–450 K and D = 20–40 MGy, the mechanical load causes almost the same deformations (ε_{l max}) of nonirradiated and irradiated samples; at T = 450–550 K, deformations of films sharply increase, and the character of their dependence changes. The ε_{l max} value of the initial sample increases almost linearly with temperature by a factor of 10, whereas the character of changing ε_{l max}(T) of the irradiated films is more complex, and its value increases approximately by a factor of 4. For T > 500 K, the deformation reaches limiting values. Irradiation increases the intensity of IR-spectra by 2–6 times and essentially increases the widths of absorption bands at 720, 1380, and 1775 cm⁻¹, which is caused by the formation of hydrogen bonds and cycles with nitrogen as well as by the formation of nitrogen oxides. External loading applied to film rupture causes an increase in the EPR signal amplitude from 3·10³ to 5·10³, which is connected with an increased concentration of radicals =N-H and-NH ₂. The electron irradiation of the polyimide films with their subsequent mechanical loading causes the spectrum lines to displace from 3475.0 to 3512.5 cm⁻¹ with simultaneous reduction of the signal amplitude from 6·10³ to 4·10³. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 52–58, February, 2007.     

Nature of the low-temperature anomalies in the physical properties of the intermediate-valent compound SmB6

The transport properties (Hall coefficient, thermopower, and resistivity) of high-quality single-crystal samples of the classical mixed-valent compound SmB₆ are investigated over a broad temperature range (1.6–300 K) in magnetic fields up to 45 T for the first time following the quasioptical measurements in the 0.6–4.5 meV frequency range [B. Gorshunov, N. Sluchanko, A. Volkov et al., submitted to Phys. Rev. B (1998)]. Measurements in the intrinsic conduction region permit determination of the gap width E _g ≈20 meV and evaluation of the behavior of the mobility and concentration of light and heavy charge carriers, as well as the temperature dependence of the carrier relaxation time, in samarium hexaboride. The results of experimental investigations in the “impurity” conduction region (E _ex≈3.5 meV) are discussed within the Kikoin-Mishchenko exciton-polaron model of charge fluctuations. Arguments supporting the formation of a metallic state with an electron-hole liquid in SmB₆ at liquid-helium temperatures are presented. Zh. éksp. Teor. Fiz. 115, 970–978 (March 1999)     

Luminescent thin ZnS : Mn films

Photo-, cathodo-, β-luminescence spectra of the ZnS : Mn films and electroluminescence spectra of highly efficient d.c. diodes with SnO_x-ZnS : Mn-Cu_xS-ZnS : Mn-Al structure have been investigated. Strong dependence of intensity and structure of the luminescence band on applied voltage has been found. Results suggest that collision cannot be the only process causing luminescence of the d.c. diodes investigated. The yield of Mn luminescence in ZnS is found to be strongly electric field-dependent.     

Variable-range hopping in Fe70Pt30 catalyzed multi-walled carbon nanotubes film

Using low-pressure chemical vapour deposition (LPCVD), multi-walled carbon nanotubes (MWNTs) are grown on nanocrystalline Fe₇₀Pt₃₀ film. The Fe₇₀Pt₃₀ nanocrystalline film is deposited by vapour condensation technique. The size of the nanoparticles varies from 5–10 nm, as inferred from SEM micrographs of Fe₇₀Pt₃₀ film. SEM and TEM observations of as-grown CNTs film reveal that these are multi-walled and their diameter varies from 30–80 nm and length is of the order of several micrometers respectively. There is a structural change from ordinary geometry of CNTs to bamboo shaped as suggested by TEM image. Raman spectra shows sharp G and D bands with a higher intensity of G band showing the presence of graphitic nature of the nanotubes. An experimental study of the temperature dependence of electrical conductivity of MWNTs film is done over a wide temperature range from (293–4 K). The measured data gives a good fit to variable-range hopping (VRH) and the results are interpreted using Mott's (VRH) model. The conduction mechanism of the MWNTs film shows a crossover from the exp[ -(T_o/T)^1/4] law in the temperature range (293–110 K) to exp[ -(T_m/T)^1/3] in the low temperature range (110–4 K). This behaviour is attributed to temperature-induced transition from three-dimension (3D) to two-dimension (2D) VRH. Various Mott's parameters like characteristic temperature (T_m), density of states at Fermi level N(E_F), localization length (ξ), hopping distance (R), hopping energy (W) have also been calculated using above-mentioned model.     

Optical absorption in layered MnGaInS<Subscript>4</Subscript> single crystals

Optical absorption in MnGaInS₄ single crystals has been studied. Direct and indirect optical transitions are found to occur in the range of photon energies of 2.37–2.74 eV and in the temperature range of 83–270 K. The temperature dependence of the band gap has been determined; its temperature coefficients E _gd and E _gi are −5.06 × 10⁻⁴ and −5.35 × 10⁻⁴ eV/K, respectively. MnGaInS4 single crystals exhibit anisotropy in polarized light at the absorption edge; the nature of this anisotropy is explained.