Growth and radioluminescence of metal elements doped LiCaAlF6 single crystals for neutron scintillator

The ns²-type metal elements (Pb and Sn) doped LiCaAlF₆ single crystals were grown by a micro-pulling-down (μ-PD) method. Pb doped LiCaAlF₆ [Pb:LiCAF] crystals showed high transparency and single phase of the LiCAF structure. However, we could not obtain Sn:LiCAF crystals due to the evaporation of SnF₂ during the crystal growth. There was an absorption peak around 193 nm in the transmittance spectrum of Pb:LiCAF crystal. In the radioluminescence spectrum of the Pb:LiCAF crystal under X-ray irradiation, two emission peaks around 200 and 830 nm were observed.     

Eu and Rb co-doped LiCaAlF6 scintillators for neutron detection

Eu and Rb co-doped LiCaAlF₆ (LiCAF) single crystals with different dopant concentrations were grown by the micro-pulling-down method for neutron detection. Their transmittance spectra showed strong absorption bands at 200–220 and 290–350 nm, and under ²⁴¹Am alpha-ray excitation, their radioluminescence spectra exhibited an intense emission peak at 373 nm that was attributed to the Eu²⁺ 5d–4f transition. These results were consistent with those for the Rb-free Eu:LiCAF. The highest light yield among the grown crystals was 36,000 ph/n, which was 20% greater than that of the Rb-free crystal. In addition, the neutron-excited scintillation decay times were 650–750 ns slower than that of the Rb-free Eu:LiCAF.     

Evaluation of Ce3+ and alkali metal ions Co-doped LiSrAlF6 crystalline scintillators

High scintillation efficiency of Eu-doped LiSrAlF₆ (LiSAF) and LiCaAlF₆ (LiCAF) codoped with alkali metal ions has been reported in our recent studies. Thus in this paper, we demonstrated the scintillation properties of 1% Ce-doped LiSAF crystals with 1% alkali metal ions co-doping to increase the light yield and understand the scintillation mechanism. The crystals showed intense emission band corresponding to the 5d-4f transition of Ce³⁺, and their light yields under thermal neutron excitation were higher than that of the Ce only doped crystal. Especially, the light yield of Ce–Na co-doped crystal exceeded about two times that of Ce only doped one.     

Effect of Eu and Pb doping on the dosimetric properties of LiCAF

LiCaAlF₆ (LiCAF) crystals doped with two different ions (europium and lead) have been investigated as potential new dosimetric materials. The stability of thermally stimulated luminescence (TSL) glow peaks in LiCAF:Eu was evaluated by means of the initial rise technique. The decay times at room temperature of the traps related to the dosimetric glow peaks were found to range between 40 and 2 × 10⁴ years confirming the good dosimetric characteristics of this crystal. The glow curve of LiCAF:Pb is dominated by a peak at approximately 300 °C emitting in the UV region (³P_0,1–¹S₀ transition of Pb²⁺) superimposed to a very broad structure at lower temperature (20–200 °C) featuring recombination at an intrinsic defect centre. The anomalous behavior of the low temperature structure during thermal cleaning procedures prevented any reliable numerical analysis of the TSL glow peak at 300 °C.     

Photoluminescence and radioluminescence study of Eu and Mn doped RbMgF3 nanoparticles

Photoluminescence (PL) and radioluminescence (RL) measurements were made on RbMgF₃ nanoparticles doped with Mn or Eu. We find that the Mn doped samples contain only Mn²⁺ and the Eu doped samples contained Eu³⁺ and Eu²⁺. The Mn²⁺ PL lifetimes are nearly independent of Mn²⁺ concentration but the RL spectra increases at high doses for 1% Mn²⁺ and decreases slightly at high doses for 5% Mn²⁺. The 5% Mn²⁺ is more radiation hard and the integrated RL intensity only starts to significantly decrease above 1 kGy. The Eu doped sample displays a PL lifetime that is lower for high Eu concentrations and this can be accounted for by a model where there is energy transfer between Eu³⁺ and more nonradiative decay sites at the surface. The RL is independent of dose between 10 mGy and ∼200 Gy, where the 1% Eu sample is more radiation hard and the Eu³⁺ RL intensity has decreased by only 3.4% at 6.7 kGy.     

One-step reverse precipitation synthesis of water-dispersible superparamagnetic magnetite nanoparticles

A convenient method for preparation of pure and doped yttrium oxide was developed, which is based on irradiation of solutions containing yttrium nitrate and ammonium formate with UV light or accelerated electrons. Solid phase formed under irradiation was consequently calcined at 500?°C or higher temperatures to obtain nanocrystalline yttrium oxide. Addition of small amount of cerium(III) or europium(III) nitrates to irradiated solutions resulted in doping of yttrium oxide with Ce(III) or Eu(III) ions. Under both types of irradiation, the method yields material with high specific surface area, consisting of spherical nanoparticles 25?C100?nm in diameter depending on preparative conditions and post-radiation treatment and with narrow size distribution. In the doped oxides (Y₂O₃:Ce or Y₂O₃:Eu), radioluminescence spectra typical for Ce³⁺ or Eu³⁺ doped oxide structures were observed.     

Luminescence and scintillation of Eu2+‐doped high silica glass

High silica glass doped with Eu²⁺ ions was prepared as a scintillating material by impregnation of Eu ions into a porous silica glass followed by reduction sintering in CO atmosphere. A dominant emission band of the Eu²⁺ 5d–4f transition peaking around 430 nm was observed in the luminescence spectrum with the excitation peak around 280 nm and no emission from Eu³⁺ was present. Photoluminescence decay kinetics was governed by decay times of a few microseconds. The Eu²⁺‐doped high silica glass exhibited comparable energy resolution and slightly higher photoelectron yield with respect to the Bi₄Ge₃O₁₂ crystal in the pulse height spectra for X‐ray photon energies within 22–60 keV. Furthermore, a factor of 1.2 higher radioluminescence intensity was observed as well. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Comparative study of Tm-doped and Tm-Sc co-doped Lu3Al5O12 scintillator

The crystals of Tm doped and Tm-Sc co-doped Lu₃Al₅O₁₂ (LuAG) grown by the floating zone (FZ) method were examined for their optical and scintillation properties. In transmittance spectra, strong absorption lines due to Tm³⁺ 4f–4f transitions were observed. X-ray excited radioluminescence spectra were measured and broad and sharp emission peaks were detected. The former one was attributed to Sc³⁺ and the latter one was due to Tm³⁺ 4f–4f transitions. Scintillation yield enhancement due to Sc co-doping was observed by means of ¹³⁷Cs pulse height spectra. Scintillation decay times were several tens of μs under pulse X-ray excitation.     

Crystal growth and luminescence properties of Pr-doped LuLiF4 single crystal

0.1, 1, and 3% Pr (with respect to Lu) doped LuLiF₄ (Pr:LuLiF₄) single crystals were grown by the micro-pulling-down (μ-PD) method. Transparency of the grown crystals was higher than 70% in the visible wavelength region with some absorption bands due to Pr³⁺ 4f-4f transitions. Intense absorption bands related with the Pr³⁺ 4f-5d transitions were observed at 190 and 215 nm. In radioluminescence spectra, Pr³⁺ 5d-4f emissions were observed at 220, 240, 340, and 405 nm. In the pulse height spectra recorded under ¹³⁷Cs γ-ray excitation, the Pr 3% doped sample showed the highest light yield of 2050 photons/MeV and the scintillation decay time of it exhibited 23 and 72 ns also excited by ¹³⁷Cs γ-ray.     

Mn和N共掺ZnO稀磁半导体薄膜的研究

使用对Zn₂N₃:Mn薄膜热氧化的方法成功制备了高含N量的Mn和N共掺ZnO的稀磁半导体薄膜.在没有N离子共掺的情况下,ZnO:Mn薄膜的铁磁性非常微弱;如果进行N离子的共掺杂,就会发现ZnO:Mn薄膜在室温下表现出非常明显的铁磁性,饱和离子磁矩为0.23 μ_B—0.61 μ_B.这说明N的共掺激发了ZnO:Mn薄膜中的室温铁磁性,也就是受主的共掺引起的空穴有利于ZnO中二价Mn离子的铁磁性耦合,这和最近的相关理论研究符合很好. 关键词： 磁性半导体 受主掺杂 空穴媒介的铁磁性     

Oxygen vacancy and dopant concentration dependent magnetic properties of Mn doped TiO2 nanoparticle

Mn doped TiO₂ nanoparticles are synthesized by sol–gel method. Incorporation of Mn shifts the diffraction peak of TiO₂ to lower angle. The position and width of the Raman peak and photoluminescence intensity of the doped nanoparticles varies with oxygen vacancy and Mn doping level. The electron spin resonance spectra of the Mn doped TiO₂ show peaks at g = 1.99 and 4.39, characteristic of Mn²⁺ state. Reduction in the emission intensity, on Mn doping, is owing to the increase of nonradiative oxygen vacancy centers. Mn doped TiO₂, with 2% Mn, shows ferromagnetic ordering at low applied field. Paramagnetic contribution increases as Mn loading increases to 4% and 6%. Temperature dependent magnetic measurement shows a small kink in the ZFC curve at about 40 K, characteristic of Mn₃O₄. The ferromagnetic ordering is possibly due to the interaction of the neighboring Mn²⁺ ions via oxygen vacancy (F⁺ center). Increase in Mn concentration increases the fraction of Mn₃O₄ phase and thereby increases the paramagnetic ordering.     

Emission spectra of MgSO4:Dy,MgSO4:Tm and MgSO4:Dy,Mn phosphors

MgSO₄:Dy, MgSO₄:Tm and MgSO₄:Dy,Mn thermoluminescence (TL) phosphors have been prepared and their emission spectra were measured using a linear heater and optical multichannel analyzer. Emission bands at about 480, 580 and 660 nm of MgSO₄ doped with Dy were observed in three dimension (3D) glow curve. Emission bands about 360, 460, and 660 nm were observed in a 3D glow curve of MgSO₄ doped with Tm. The emission spectra of MgSO₄:Dy and MgSO₄:Tm are attributed to the characteristic emission wavelengths from transitions of Dy³⁺ and Tm³⁺ respectively. The results show that the structures of traps in matrix materials determine the activation energy distribution and dopant energy levels of rare earth ions are related with the emission spectrum wavelengths of sulfate phosphors. The intensities of the glow peaks in both bands at about 480 and 580 nm in MgSO₄ doped Dy and Mn were dramatically reduced in comparison with that of MgSO₄ doped Dy except above 300°C. It means that the trapping structures of MgSO₄ :Dy phosphor has greatly been altered by the co-dopant Mn but no change is observed in wavelengths of the emission spectra.     

Synthesis and conductivities of the apatite-type systems, La9.33+xSi6−yMyO26+z (M=Co, Fe, Mn) and La8Mn2Si6O26

Apatite-type oxides of formula (La/Sr)_10−xSi₆O_26+y have been attracting significant interest recently, because of their high oxide ion conductivity. In this paper we report the synthesis and conductivities of phases based on doping La_9.33Si₆O₂₆ with Co, Fe, Mn on the Si site, according to the formula La_9.33+x/3Si_6−xM_xO₂₆ (M=Co, Fe, Mn). Substitution limits observed were x≤1.5 (Co), x≤1.25 (Fe), x≤0.5 (Mn). Higher Mn levels could be achieved by substituting onto the La site, with it being possible to prepare the phase La₈Mn₂Si₆O₂₆. The highest conductivities were observed for the Co doped samples, although investigations into the dependence of conductivity on p(O₂) (0.2–10⁻⁵ atm.) indicated that the conductivity was dominated by the electronic component in these cases. In contrast, the conductivities for the Fe and Mn doped samples were mainly ionic in the same p(O₂) range. Experiments into varying the oxygen content of these doped phases indicated that increasing the oxygen content above the nominally stoichiometric O₂₆ appears to increase the oxide ion conductivity. Preliminary studies of the reactivity of the electrolyte La_9.33Si₆O₂₆ with potential SOFC cathode materials (La_1−xSr_xMO₃; M=Co, Fe, Mn) suggests that reaction can occur at high temperatures leading to the incorporation of the transition metal into the apatite electrolyte. However, the fact that these doped phases exhibit high conductivities suggests that this may limit any problems caused by such a reaction at the electrolyte-electrode interface. Paper presented at the 8th EuroConference on Ionics, Carvoeiro, Algarve, Portugal, Sept. 16–22, 2001.     

Optical characterization of gallium antimonide highly doped with manganese

Gallium antimonide crystals highly doped with Mn were prepared by a liquid-phase-electroepitaxy growth method. The crystals exhibited high hole concentrations up to 6×10¹⁸ cm⁻³. Photoluminescence (PL) and transmission techniques were used for their investigation. Spectral line-shapes typical for highly doped semiconductors were observed. The lines revealed the features corresponding to band gap narrowing and valence-band filling phenomena. Values of the band-gap narrowing ΔE_g and the degree of the valence-band filling ΔE_F were estimated from the PL spectra. The ionization energy of the Mn acceptor E_i was estimated to be approximately 15.1-15.6 meV. At low temperatures, the PL maxima shifted relatively strongly towards higher energy with temperature. The shifts most probably resulted from a dramatic change in the electron density of states near the bottom of the conduction band. The extent of low-energy tails of the PL bands correlates with the doping levels. The transmission spectra exhibited an absorption band centred at around 774-780 meV. The band most probably originated in electron transitions from the level of spin-orbit splitting to the top of the valence band.     

Preliminary TL Studies of K2GdF5:Dy3+ exposed to photon and neutron radiation fields

Results of the investigation concerning thermoluminescence (TL) responses to X, gamma and neutron radiation fields for crystals of complex fluoride K₂GdF₅ undoped and doped with varying concentrations of Dy³⁺ ions are presented. Crystals doped with 5.0 at% Dy³⁺ have shown the most efficient TL response, with a linear response to doses for all the radiation fields. In the X rays range, the maximum TL response has been found to be 15 times more than the response for gamma. The fast and thermal neutron TL outputs were evaluated for K₂Gd_0.95Y_0.05F₅ and the contribution of the gamma component in the TL curve was estimated.     

Significantly reduced leakage currents in organic thin film transistors with Mn‐doped Bi2Ti2O7 high‐k gate dielectrics

We report the fabrication of organic thin‐film transistors (OTFTs) with high‐k gate dielectrics of Mn‐doped Bi₂Ti₂O₇ (BTO) films. 3% Mn‐doped BTO films deposited on polymer substrates by pulsed laser deposition at room temperature exhibit low leakage currents of 2.1 × 10^–8 A/cm² at an applied electric field of 0.3 MV/cm, while undoped BTO films show much higher leakage currents of 4.3 × 10^–4 A/cm². Mn doping effectively reduces the number of oxygen vacancies in the films and improves the electrical properties. Low operation voltage and significantly reduced leakage currents are demonstrated in pentacene‐based OTFTs with the Mn‐doped BTO gate dielectrics. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Thermally stimulated luminescence of Ca3(PO4)2 and Ca9Ln(PO4)7 (Ln = Pr,Eu, Tb,Dy, Ho,Er, Lu)

The series of whitlockite compounds Ca₃(PO₄)₂ and Ca₉Ln(PO₄)₇ (Ln = Pr, Eu, Tb, Dy, Ho, Er, Lu) was studied in radioluminescence (RL) and thermally stimulated luminescence (TSL) excited by X-rays. f-f emission lines of Ln³⁺ were observed in RL for Ca₉Ln(PO₄)₇ (Ln = Pr, Eu, Tb, Dy, Ho, Er) whereas d-d emission band of the impurity Mn²⁺ was observed in Mn:Ca₃(PO₄)₂ and Mn:Ca₉Lu(PO₄)₇ at 655 nm. In TSL, the Eu, Ho and Er compounds did not show any signal. As Eu³⁺, Ho³⁺ and Er³⁺ present the highest Ln³⁺/Ln⁴⁺ ionization potential (IP) of the series, this was interpreted as the inability of these lanthanides to trap a hole. On the contrary Pr³⁺ in Ca₉Pr(PO₄)₇, Tb³⁺ in Ca₉Tb(PO₄)₇, Dy³⁺ in Ca₉Dy(PO₄)₇, Mn²⁺ in Mn:Ca₃(PO₄)₂ and Mn:Ca₉Lu(PO₄)₇ were identified as hole traps and radiative recombination centers in the TSL mechanism. Ca₉Tb(PO₄)₇ was found to be a high intensity green persistent phosphor whereas Mn:Ca₉Lu(PO₄)₇ is a red persistent phosphor suitable for in vivo imaging application.     

Optical properties of sol-gel fabricated Mn/SiO2 nanocomposites: Observation of surface plasmon resonance in Mn nanoparticles

Manganese nanoparticles were grown in silica glass and silica film on silicon substrate by annealing of the sol-gel prepared porous silicate matrices doped with manganese nitrate. Annealing of doped porous silicate matrices was performed at various conditions that allowed to obtain the nanocomposite glasses with various content of metallic Mn. TEM of Mn/SiO₂ glass indicates the bimodal size distribution of Mn nanoparticles with mean sizes of 10.5 nm and 21 nm. The absorption and photoluminescence spectra of Mn/SiO₂ glasses were measured. In the absorption spectra at 300 nm (4.13 eV) we observed the band attributed to the surface plasmon resonance in Mn nanoparticles. The spectra proved the creation of Mn²⁺ and Mn³⁺ ions in silica glass as well. The absorption spectra of Mn/SiO₂ glasses annealed in air prove the creation of manganese oxide Mn₂O₃. The measured reflection spectra of Mn/SiO₂ film manifest at 240-310 nm the peculiarity attributed to surface plasmons in Mn nanoparticles.     

Recombination luminescence process in NaCl

The recombination luminescence in NaCl crystals pure and doped with Cu⁺ and Mn⁺⁺ has been studied. A unique mechanisme that implies the recombination V_K-electron is proposed to explain the thermoluminescence as well as the radioluminescence and the after-glow following an irradiation.     

Investigation of dielectric and electrical behavior of Mn doped YCrO3 nanoparticles synthesized by the sol gel method

In the present work Mn doped YCrO₃ nanoparticles are synthesized by the sol–gel method. Samples have been characterized by the X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV–vis absorption spectroscopy. The optical band gap of Mn doped YCrO₃ nanoparticles increases with increase of doping concentration. The dc resistivity of the prepared samples decreases with increasing temperature. The variation of ac conductivity with frequency has been explained by the Correlated Barrier Hoping (CBH) conduction mechanism. Dielectric permittivity of the samples was studied and it follows the power law ε^/(f)∝Tⁿ, where the temperature exponent n is found to be frequency dependent. The dielectric properties of the samples have been discussed in terms of electric modulus vector. Both activation energies due to dc resistance and dielectric response have been measured for the different samples and it is observed that it increases with the Mn content.