PIXE detection limits for dental enamel from some human teeth by excitation with protons and He ions from a 3 MeV Van der Graaff accelerator

A technique has been developed to measure elemental content in human teeth using H⁺ and ⁴He²⁺ ion beam analysis. Teeth of Oradea inhabitants were sampled in two stomatological clinics in Oradea in the period of 2004 and 2005 years. Tooth samples were irradiated in vacuum with 2 MeV proton and 3 MeV alpha beams from a Van der Graaff electrostatic accelerator of EG-5 experimental facility in FLNP, JINR. The particle induced X-ray emission (PIXE) analysis, apart from determination of Ca, allowed an optimised detection of Cr, Cu, Fe and Zn above the detection limits by the use of Al and Mylar filters. The detection limits for K_α X-rays using proton and alpha beams are determined and discussed.     

Characterization of electron irradiated GaN n-p diode

Electron-beam irradiated GaN n⁺-p diodes were characterized by deep level transient spectroscopy (DLTS) and optical responsivity measurements. The GaN n⁺-p diode structures were grown by metal organic chemical vapor deposition technique, and the electron irradiation was done by the energies of 1 MeV and 2 MeV with dose of 1 × 10¹⁶ cm^− 2. In DLTS measurement, the defect states of E_c − 0.36 eV and E_c − 0.44 eV in the electron irradiated diodes appeared newly. The optical responsivity of GaN n⁺-p diode was characterized in ultra-violet region, and then the maximum optical responsivity at 350 nm was decreased after electron-beam irradiation.     

Status and overview of production target for BigRIPS separator at RIKEN

A water-cooled high-power rotating disk target is employed at the in-flight radioactive-isotope (RI) beam separator (BigRIPS), RIKEN. For a ²³⁸U primary beam with energy of 350 A MeV and an intensity of 1 particle μA bombarding a beryllium or carbon target disk with a 1 g/cm² thickness, a total heat loss of 28 GW/m² on the target surface is estimated for a beam-spot size of 1 mm in diameter.For the development of a suitable target assembly, a test bench was constructed and has been used for the present RI beam separator (RIPS). A beam spot temperature monitor using an infrared thermo-viewer with telescope lens was developed. The measured temperature for some high-power beam experiments corresponded to results of computer simulations. A radiation hardness test of the magnetic fluid used for a vacuum-tight rotating actuator was performed by irradiating with intense γ-ray converted from an electron beam. No significant change of viscosity was observed up to the total dose of 0.7–1.8 MGy.Based on these studies, a practical target system for the BigRIPS separator was designed. To facilitate the maintenance of the target system in a high-radiation environment, a remote-handling maintenance cart system is considered.     

Development of a cryogenic gas target for intense RI beam production at CRIB

Nuclear reactions of astrophysical interest, especially those under high-temperature and high-density conditions, require high-intensity low-energy radioactive ion beams, because the cross-sections are very small for the direct method study. Production of high-intensity radioactive ion beams is, therefore, one of the key developments for RI beam facilities.We report the development of a new cryogenic RI beam production gas target, along with its characteristics and performance. Some of its advantages are the increased stability against high-current primary beams and the increased thickness due to the cooling by liquid nitrogen.The target is being tested with heavy-ion beams. Measures by energy loss of the beam indicate that a thickness of about 2.4 mg/cm² of H₂ gas has been attained and a secondary beam of ⁷Be⁴⁺ at 4.0 MeV/u of more than 2×10⁸ pps was produced.     

Near UV-based LED fabricated with Ba5SiO4(F,Cl)6:Eu as blue- and green-emitting phosphor

A series of halosilicate phosphor, Ba₅SiO₄(F,Cl)₆:Eu²⁺, were synthesized by a solid state reaction. Excited by 370-nm light, Ba₅SiO₄Cl₆:Eu²⁺ exhibits a broad emission band peaking at 440 nm. Partial substitution of Cl⁻ with F⁻ in the host lattice leads to red-shift in the emission band with centering wavelength from 440 nm to 503 nm. The possible mechanism for the luminescence change was discussed based on the XRD patterns. Blue and green LEDs were fabricated by combination of a 370 nm-emitting near UV chip and the optimal Ba₅SiO₄Cl₆:Eu²⁺ and Ba₅SiO₄(F₃Cl₃):Eu²⁺, respectively. This series of phosphors is considered as a promising blue and green component used in fabrication of near UV-based white LEDs.     

Luminescence behavior of Dy ions in lead borate glasses

Dy-doped lead borate glasses were studied. The luminescence spectra showed two characteristic bands at 480 and 573 nm due to ⁴F_9/2–⁶H_15/2 (blue) and ⁴F_9/2–⁶H_13/2 (yellow) transitions of Dy³⁺. The yellow/blue luminescence of trivalent dysprosium was analyzed as a function of the B₂O₃/PbO ratios, the activator (Dy³⁺) and the PbX₂ (X = F, Cl, Br) content.     

The Chandigarh variable energy cyclotron

The characteristics and performance of the variable energy cyclotron at Chandigarh have been described. The machine operates for protons at 1 to 5 MeV, for deuterons at 4 MeV, for alphas from 1 to 2 MeV and 7 to 8 MeV, and He³⁺⁺ upto 11 MeV. The resolved beams of different particles from 30 nA to 1 μA have been obtained at the target with a resolution of about 30 keV. The magnetic field and the beam profile in the chamber are discussed. Various gamma-ray and charged particle spectra are given to indicate the performance of the accelerator.     

Structure and thermal properties of transparent conductive nanoporous F:SnO2 films

The nanoporous F:SnO₂ materials prepared for the purpose of dye-sensitized solar cells (DSCs) application are composed of SnCl₄ (98.0%) and HF (48-51%), produce with a NH₄OH aqueous solution with sol-gel method as a catalyst. Acetylene black is needed to make nano-porous from FTO heated until 120 °C that will change it from sol to gel and with that 2 phase sintering with 500 °C and 550 °C can be predicted to produce nano-materials. The preferred orientation indicates (110), (101), (211) for SnO₂ and (200) for fluorine, respectively. The main IR features include resonances at 660, 620 and 540 cm^− 1. From the FE-SEM results, the mean pore size of the sample is range of 16-38 nm. Finally, the nanoporous F:SnO₂ film used for TCO layer of dye-sensitized solar cells (DSCs) exhibited an energy conversion efficiency of about 1.83% at light intensity of 100 mW/cm².     

Preparation of SrAl2O4: Eu, Dy nanometer phosphors by detonation method

SrAl₂O₄: Eu²⁺, Dy³⁺ nanometer phosphors were synthesized by detonation method. The particle morphology and optical properties of detonation soot that was heated at different temperatures (600–1100 °C) had been studied systematically by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Results indicated SrAl₂O₄: Eu²⁺, Dy³⁺ nanometer powders in monoclinic system (a = 8.442, b = 8.822, c = 5.160, β = 93.415) can be synthesized by detonation method, when detonation soot was heated at 600–800 °C. The particle size of SrAl₂O₄: Eu²⁺, Dy³⁺ is 35 ± 15 nm. Compared with the solid-state reaction and sol-gel method, synthesis temperature of the detonation method is lower about 500 and 200 °C respectively. After being excited under UN lights, detonation soot and that heated at 600–1100 °C can emit a green light.     

Emissions properties of Ho: I7 → I8 transition sensitized by Er and Yb in fluorophosphate glasses

Emission properties of Ho³⁺ at 2.0 μm and the energy transfer mechanism between Yb³⁺, Er³⁺ and Ho³⁺ ions in fluorophosphate glasses are investigated. The measured emission spectra show that the ⁵I₇ → ⁵I₈ transition of Ho³⁺ upon 980 nm laser diode excitation is strong. Judd–Ofelt intensity parameters (Ω_λ, λ = 2, 4, 6), spontaneous transition probability (A_rad), radiative lifetime (τ_r), absorption cross section (σ_a), stimulated emission cross section (σ_e) and FWHM ×  for the transition of Ho³⁺: ⁵I₇ → ⁵I₈ are calculated and discussed. The obtained results show that the present Yb³⁺/Er³⁺/Ho³⁺ triply-doped fluorophosphate glass can be identified to be a promising material at 2.0 μm emission.     

Luminescent properties of Ca2BO3Cl:Eu yellow-emitting phosphor for white light-emitting diodes

The Ca₂BO₃Cl:Eu²⁺ phosphor was synthesized by the general high temperature solid-state reaction and an efficient yellow emission under near-ultraviolet and blue excitation was observed. The emission spectrum shows a single intense broad emission band centered at 573 nm, which corresponds to the allowed f-d transition of Eu²⁺. The excitation spectrum is very broad extending from 350 to 500 nm, which is coupled well with the emission of UV LED (350-410 nm) and blue LED (450-470 nm). The measured emission of In-GaN-based Ca₂BO₃Cl:Eu²⁺ LED shows white light to the naked eye with a chromatic coordinate of (0.33, 0.36). The Ca₂BO₃Cl:Eu²⁺ is a very appropriate yellow-emitting phosphor for white LEDs.     

EPR and vibrational studies of YVO4:Tm, Yb single crystal

A well oriented YVO₄ single crystal, with 5% Yb³⁺ and 2% Tm³⁺ nominal doping, was investigated using the Raman and EPR techniques.The EPR measurements suggest that Yb³⁺ ions occupy eight-coordinated Y³⁺ sites forming bisdisphenoids of the D_2d symmetry. An inhomogeneous distribution of rare-earth ions leads to a significant distortion of the local point symmetry (C₁). It seems that strong dipole–dipole interactions between Yb³⁺ ions are responsible for the distortion. As a result, two types of ytterbium magnetic centers appear. They correspond to paired magnetic centers and distorted isolated paramagnetic centers that are strongly sensitive to the magnetic field directions and some imperfections of the crystal. Pair centers can be recorded through the rotation around the c-crystal axis, whereas isolated centers can be measured when the crystal is rotated around the a-crystal axis. With the increasing temperature, the ytterbium signal disappeared at about 23 K and a group of narrow lines became visible. These lines, observed in the range of 240–550 mT, correspond to the Gd³⁺ (S = 7/2) ions, doped to the structure unintentionally from the basic materials.     

VUV spectroscopy of wide bandgap materials

In this paper we will present VUV spectroscopy experiments performed at the Superlumi station of Hasylab, DESY, Hamburg, on samples of BaF₂ crystals activated with Ce and BaF₂, (Ba,La)F₂ crystals activated with Er. The results of these experiments include time resolved luminescence and luminescence excitation spectra obtained under wavelength selective VUV and UV excitation by pulsed synchrotron radiation.We will reveal the information provided by the VUV/UV excitation spectra of the Ce³⁺ 5d → 4f as well as Er³⁺ 4fⁿ⁻¹5d → 4fⁿ and 4fⁿ → 4fⁿ emissions on energy transfer mechanisms from the fluoride host to the rare earth ion. We will demonstrate that the fast energy transfer channels involve bound excitons while the generation of free electrons and holes leads to slower processes dependant on hole and/or electron trapping.We will demonstrate that differences between the excitation spectra of the 5d → 4f emission in Ce and 4f¹⁰5d → 4f¹¹ emission in Er activated BaF₂ are generated by the coupling of the 4f → 5d transition to the 4f¹⁰ core of the Er³⁺ ion. We will also identify the additional band, absent for Ce, which is due to the exchange split high spin (HS) state of the 4f¹⁰5d configuration responsible for the slow decay of the excited Er³⁺ ions in BaF₂ and (Ba,La)F₂.Finally we will provide evidence and explain why the dominant VUV 4f¹⁰5d → 4f¹¹ Er³⁺ emission in BaF₂ is spin-forbidden and slow while in the mixed (Ba,La)F₂ crystals it is spin-allowed and fast.     

Preparation of Pa targets

²³¹Pa is an alpha-emitter belonging to the actinide group. Because it is both toxic and highly radioactive, it requires special precautions during target fabrication. The isotopic material was available in the chemical form of dried nitrate. It had to be converted to Pa-oxide, which is our most favourable source material for the preparation of actinide targets. Targets in the thickness range between 70 and 100 μg/cm² were produced by cold crucible electron beam evaporation–condensation on different backings and target frames.     

Study on ZnGa2O4:Cr a.c. powder electroluminescent device

An a.c. powder electroluminescent (EL) device using ZnGa₂O₄:Cr³⁺ phosphor was fabricated by the screen printing method. Optical and electrical properties of the device were investigated. The fabricated device shows a red emission at 695 nm driven by the a.c. voltage. The emission is attributed to the energy transfer from hot electrons to Cr³⁺ centers via self-activated Ga-O groups. Luminance (L) versus voltage (V) matches the well-known equation of L = L₀exp(− bV ^− 1 / 2) and luminance increases proportionally with frequency due to the increase of excitation probability of host lattice or Cr³⁺ centers. The diagram of the charge density (Q) versus applied voltage (V) is based on a conventional Sawyer-Tower circuit. At 280 V and 1000 Hz, the luminance and the luminous efficiency of the fabricated powder EL device are about 1.0 cd/m² and 13 lm/W, respectively. And under the high field, the device fabricated with the oxide-based phosphor of ZnGa₂O₄:Cr³⁺ shows excellent stability in comparison with the conventional sulfide powder EL device.     

Influence of calcination temperature on luminescent properties of Sr3Al2O6:Eu, Dy phosphors prepared by sol–gel-combustion processing

The detailed preparation process of Eu²⁺ and Dy³⁺ ion co-doped Sr₃Al₂O₆ phosphor powders with red long afterglow by sol–gel-combustion method in the reducing atmosphere is reported. X-ray diffraction, scanning electron microscopy and photoluminescence spectroscopy are used to investigate the effects of synthesis temperature on the crystal characteristics, morphology and luminescent properties of the as-synthesized Sr₃Al₂O₆:Eu²⁺, Dy³⁺ phosphors. The results reveal that Sr₃Al₂O₆ crystallizes completely when the combustion ash is sintered at 1200 °C. The excitation and the emission spectra indicate that the excitation broad-band lies chiefly in visible range and the phosphor powders emit strong light at 618 nm under the excitation of 472 nm. The light intensity and the light-lasting time of Sr₃Al₂O₆:Eu²⁺, Dy³⁺ phosphors are increased when increasing the calcination temperatures from 1050 to 1200 °C. The afterglow of Sr₃Al₂O₆:Eu²⁺, Dy³⁺ phosphors sintered at 1200 °C lasts for over 600 s when the excited source is cut off. The red emission mechanism is discussed according to the effect of nephelauxetic and crystal field on the 4f⁶5d¹ → 4f⁷ transition of the Eu²⁺ ions.     

Sr3.5Mg0.5Si3O8Cl4: Eu bluish-green-emitting phosphor for NUV-based LED

Sr₄Si₃O₈Cl₄:Eu²⁺ and Sr_3.5Mg_0.5Si₃O₈Cl₄:Eu²⁺ phosphors were prepared by a conventional solid state reaction (SS). Excited by 370 nm near-ultraviolet light, the phosphors show an efficient bluish-green wide-band emission centering at 484 nm, which originates from the 4f5d¹ → 4f⁷ transition of Eu²⁺ ion. The excitation spectra of the phosphors are a broad band extending from 250 nm to 400 nm. Mg²⁺-codoping greatly enhances the bluish-green emission of the phosphors. An LED was fabricated by coating the Sr_3.5Mg_0.5Si₃O₈Cl₄:0.08Eu²⁺ phosphor onto an ~ 370 nm-emitting InGaN chip. The LED exhibits bright bluish-green emission under a forward bias of 20 mA. The results indicate that Sr_3.5Mg_0.5Si₃O₈Cl₄:0.08Eu²⁺ is a candidate as a bluish-green component for fabrication of NUV-based white LEDs.     

Studies on red-emitting Cr doped barium aluminate phosphor obtained by combustion process

Red-emitting BaAl₂O₄:Cr³⁺ phosphor material is prepared by urea combustion route in 5 min. Powder X-ray (XRD) diffraction, thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and BET surface area measurements are used to characterize the as-prepared combustion products. Electron Paramagnetic Resonance (EPR) studies have been carried out on Cr³⁺ ions in BaAl₂O₄ phosphors at room temperature and at 110 K. The number of spins participating in resonance (N) and its paramagnetic susceptibilities (χ) have also been evaluated. The excitation spectra shows two broad and intense bands corresponding to Cr³⁺ ion in octahedral symmetry. The red emission peak observed at 705 nm is identified as due to ²E_g → ⁴A_2g transition from Cr³⁺ ions. The crystal field parameter Dq and Racah inter-electronic repulsion parameters B and C have been evaluated. From the results and analyses of the EPR and optical studies, the site symmetry of Cr³⁺ ion in this phosphor is attributed to a distorted octahedron.     

Luminescence and energy transfer of Mn co-doped SrSi2O2N2:Eu green-emitting phosphors

Eu²⁺ and Mn²⁺ co-doped SrSi₂O₂N₂ green-phosphors, with promising luminescent properties (examined by their powder diffuse reflection, photoluminescence excitation and emission spectra) suitable for UV converted white LEDs, were produced by high temperature solid-state reaction method. The produced materials exhibited intense broad absorption bands at 220–500 nm and a broad emission band centered at ca. 530 nm, attributed to 4f–5d transitions of Eu²⁺. The emission intensity of Eu²⁺ ions was greatly enhanced by introducing Mn²⁺ ions into SrSi₂O₂N₂:Eu²⁺ due to the energy transfer from Mn²⁺ to Eu²⁺. The energy transfer probability from Mn²⁺ to Eu²⁺ depends strongly on the Mn²⁺ concentration, which is maximized at a Mn²⁺ concentration of 3 mol%. It drastically decreases for higher concentrations. The results indicated that SrSi₂O₂N₂:Eu²⁺, Mn²⁺ is a promising green-emitting phosphor for white-light emitting diodes with near-UV LED chips.     

Novel highly luminescent europium dinitrosalicylates

A series of lanthanide dinitrosalicylates M₃Ln(3,5-NO₂-Sal)₃ · nH₂O (Ln = Eu, Gd; M = Li, Na, K, Cs) was synthesized. It was found that the luminescence efficiency of some M₃Eu(3,5-NO₂-Sal)₃ · nH₂O compounds was near to the high efficiency of europium dibenzoylmethanate with 1,10-phenanthroline, Eu(DBM)₃ · Phen. The luminescence excitation spectra, electron-vibrational luminescence spectra, and vibrational IR spectra were investigated. The energy of the lowest excited triplet state of the ligand was obtained from phosphorescence spectra of M₃Gd(3,5-NO₂-Sal)₃ · nH₂O, M(3,5-NO₂-HSal) · nH₂O, and M₂(3,5-NO₂-Sal) · nH₂O. The details of the structure of compounds were discussed. The influence of different M-cations on the Eu³⁺ luminescence efficiency and on the processes of excitation energy transfer to a Eu³⁺ ion was analyzed. The presence of large alkali metal cations in lanthanide dinitrosalicylates and an increase in the temperature weaken the network of hydrogen bonds and, to some extent, the “ligand–metal” bonds. This is a cause of a long-wavelength shift of the intraligand charge transfer (ILCT) band in Eu³⁺ excitation spectra arising at inclusion of Cs⁺ instead of Li⁺ cations in the crystal lattice and at the heating of compounds. A change of the energies of ligand electronic states at substitution of Li⁺ and Na⁺ for Cs⁺ can give a tenfold enhancement of the Eu³⁺ luminescence efficiency at 300 K.