Ca₂BO₃Cl:Ce³⁺,Tb³⁺:A novel tunable emitting phosphor for white light-emitting diode

<正>Ca₂BO₃Cl:Ce³⁺,Ca₂BO₃Cl:Tb³⁺,and Ca₂BO₃Cl:Ce³⁺,Tb³⁺ phosphors are synthesized by a high temperature solid-state reaction.The emission intensity of Ce³⁺ or Tb³⁺ in Ca₂BO₃Cl is influenced by the Ce³⁺ or Tb³⁺ doping content,and the optimum concentrations of Ce³⁺ and Tb³⁺ are 0.03 mol and 0.05 mol,respectively.The concentration quenching effect of Ce³⁺ or Tb³⁺ in Ca₂BO₃Cl occurs,and the concentration quenching mechanism is d-d interaction for either Ce³⁺ or Tb³⁺.The Ca₂BO₃Cl:Ce³⁺,Tb³⁺ can produce colour emission from blue to green by properly tuning the relative ratio between Ce³⁺ and Tb³⁺,and the emission intensity of Tb³⁺ in Ca₂BO₃Cl can be enhanced by the energy transfer from Ce³⁺ to Tb³⁺.The results indicate that Ca₂BO₃Cl:Ce³⁺,Tb³⁺ may be a promising double emission phosphor for UV-based white light emitting diodes.     

Double emitting phosphor NaSr4(BO3)3:Ce, Tb for near-UV light-emitting diodes

Blue and green double emitting phosphor, Ce³⁺ and Tb³⁺ co-doped NaSr₄(BO₃)₃, was synthesized in a weak reducing atmosphere by a conventional high temperature solid-state reaction technique. For comparison, Ce³⁺ or Tb³⁺ singly doped NaSr₄(BO₃)₃ was also prepared. The emission and excitation spectra of all samples have been investigated. NaSr₄(BO₃)₃:Tb³⁺ excitation includes a strong absorption at about 240 nm and some weak sharp lines in near-ultraviolet (n-UV) spectral region. The excitation of Ce³⁺ and Tb³⁺ co-doped NaSr₄(BO₃)₃ shows a strong broad band absorption in the n-UV region from the contribution of Ce³⁺, which makes it suitable for excitation by a n-UV LED chip. The emission of NaSr₄(BO₃)₃:Ce³⁺,Tb³⁺ consists of a blue emission band from Ce³⁺ and a green emission from Tb³⁺ under the excitation of n-UV light. Energy transfer between Ce³⁺ and Tb³⁺ is also discussed, and the relative intensity of blue emission and green emission could be tuned by adjusting the concentration of Ce³⁺ and Tb³⁺. The phosphor NaSr₄(BO₃)₃:Ce³⁺,Tb³⁺ could be considered as a double emission phosphor for n-UV excited white light-emitting diodes.     

Luminescent characteristics of LiCaBo3:M (M=Eu, Sm, Tb, Ce, Dy) phosphor for white LED

LiCaBO₃:M (M=Eu³⁺, Sm³⁺, Tb³⁺, Ce³⁺, Dy³⁺) phosphors were synthesized by a normal solid-state reaction using CaCO₃, H₃BO₃, Li₂CO₃, Na₂CO₃, K₂CO₃, Eu₂O₃, Sm₂O₃, Tb₄O₇, CeO₂ and Dy₂O₃ as starting materials. The emission and excitation spectra were measured by a SHIMADZU RF-540 UV spectrophotometer. And the results show that these phosphors can be excited effectively by near-ultraviolet light-emitting diodes (UVLED), and emit red, green and blue light. Consequently, these phosphors are promising phosphors for white light-emitting diodes (LEDs). Under the condition of doping charge compensation Li⁺, Na⁺ and K⁺, the luminescence intensities of these phosphors were increased.     

Green light emission by Ce3+ and Tb3+ co-doped Sr3MgSi2O8 phosphors for potential application in ultraviolet whitelight-emitting diodes

Sr₃MgSi₂O₈:Ce³⁺, Tb³⁺ phosphor samples were prepared using a solid-state reaction technique, and the photoluminescence properties and energy transfer were investigated. Effective energy transfer occurred in Ce³⁺/Tb³⁺ co-doped Sr₃MgSi₂O₈ phosphors. Co-doping of Ce³⁺ was found to enhance the emission intensity of Tb³⁺ to a certain extent by transferring energy to Tb³⁺. The Ce³⁺/Tb³⁺ energy transfer was thoroughly investigated through its emission/excitation spectra and photoluminescence decay behavior. The color emitted by Sr₃MgSi₂O₈:Ce³⁺, Tb³⁺ phosphors varied from blue to green and can be controlled by altering the concentration ratio of Ce³⁺ to Tb³⁺. These results indicate that Sr₃MgSi₂O₈:Ce³⁺, Tb³⁺ may be useful as a green-emitting phosphor for ultraviolet whitelight-emitting diodes.     

Photoluminescence properties and energy transfer of Ca3WO6:Sm3+ co-doped Eu3+

A reddish-orange phosphor, Ca₃WO₆:Sm³⁺, was synthesized by the convenient solid-state reaction method and characterized by X-ray diffraction (XRD). Photoluminescence properties and concentration quenching of Ca₃WO₆:Sm³⁺ phosphor have been discussed in the excitation and emission spectra. Ca₃WO₆:Sm³⁺ phosphor is able to generate a strong excitation peak, which matches the emission wavelength from near-UV LEDs. Energy transfer from Sm³⁺ to Eu³⁺ in Ca₃WO₆ host is observed and investigated in detail. The chromaticity coordinates of Ca₃WO₆:Sm³⁺ can be regulated to approach the NTSC standard values of red phosphor by codoping Eu³⁺ ions. The photoluminescence properties suggest that novel Ca₃WO₆:Sm³⁺, Eu³⁺ phosphor might have a potential application for near-UV LEDs.     

Second-order quadrupole splittings of the95Mo NMR signal in Mo(CO)6 and their reduction by sample spinning

The lifetimes of higher lying¹S_0?,¹D_2?, and¹F ₃ ⁰ -levels and of the 5s 7s³S₁- and 5p^{2 3}P₁-state in the Sr I-spectrum have been measured by a time resolved registration of the fluorescent intensity. The¹S_0? and¹D₂-levels were populated selectively by a two step optical excitation using two pulsed dye lasers. In the case of the¹F ₃ ⁰ -levels and of the³S_1?,³P₁-states the first excitation step was performed by a discharge, for the second, selective step a pulsed dye laser was used. The agreement of the experimental results with theoretically obtained lifetimes is satisfactory only in some cases.     

Enhanced optical activation of Er in Er-doped Al2O3 powders by Y codoping in a sol-gel method

Enhanced photoluminescence (PL) mechanism of Er³⁺-doped Al₂O₃ powders by Y³⁺ codoping at wavelength 1.53 μm has been investigated through PL measurements of 0.1 mol% Er³⁺- and 0-20 mol% Y³⁺-codoped Al₂O₃ powders prepared at a sintering temperature of 900 °C in a non-aqueous sol-gel method. PL intensity and lifetime of Er³⁺-Y³⁺-codoped Al₂O₃ powders composed of γ-(Al,Er,Y)₂O₃ and θ-(Al,Er,Y)₂O₃ phases increased with increasing Y³⁺-codoping concentration. The 10-20 mol% Y³⁺ codoping in 0.1 mol% Er³⁺-doped Al₂O₃ powders intensified the PL intensity by about 20 times, with a PL lifetime prolonged from 3.5 to 5.8 ms. A maximal increase of the optical activity of Er³⁺ in 0.1 mol% Er³⁺-Y³⁺-codoped Al₂O₃ powders about one order was achieved by 10-20 mol% Y³⁺ codoping. It is found that the improved PL properties for Er³⁺-Y³⁺-codoped Al₂O₃ powders are mainly attributed to enhanced optical activation of Er³⁺ in the Al₂O₃ by Y³⁺ codoping, and to the slightly increased radiative quantum efficiency of Er³⁺ in the Al₂O₃.     

Investigation of crystallographic sites of Eu in La2BaZnO5 by site-selective laser-excitation spectroscopy

La₂BaZnO₅:Eu³⁺ (0.05 mol%) was prepared by a solid-state reaction at high temperature. X-ray powder diffraction analysis confirmed the formation of single phase La₂BaZnO₅. Luminescence properties of La₂BaZnO₅:Eu³⁺ are investigated by site-selective laser-excitation and emission spectroscopy at 18 K. Two different crystallographic sites for Eu³⁺ corresponding to the La³⁺ and Ba²⁺ sites are identified from the ⁷F₀→⁵D₀ excitation spectra obtained by monitoring the ⁵D₀→⁷F_J (J=1, 2, …, 6) emissions. It is found that Eu³⁺ substituted for the Ba²⁺ ion experiences stronger crystal-field strength than Eu³⁺ substituted for the La³⁺ ion. Energy transfer between the two crystallographic Eu³⁺ centers is investigated by luminescence decay curves at 18 K.     

Preparation and Photoluminescence of Sm <Superscript>3+</Superscript> Doped YAlO <Subscript>3</Subscript> Phosphor

YAlO₃: Sm³⁺ phosphor has been synthesized by the solid state reaction method with calcium flouride used as a flux. The resulting YAlO₃: Sm³⁺ phosphor was characterized by X-ray diffraction (XRD) technique, Fourier transmission infrared spectroscopy (FTIR), photoluminescence . . PL excitation spectrum was found at 254,332,380,400,407, 603 and 713 nm. Under excitation of UV(713 nm) YAlO₃: Sm³⁺ (0–3 %) broad band emission were observed from 400 to 790 nm with a maximum around 713 nm of YAlO₃ host lattice accompanied by weak emission of Sm³⁺ (⁴G_5/2 – ⁶H_5/2, ⁶H_7/2,⁶H_9/2) transitions. The results of the XRD show that obtained YAlO₃: Sm³⁺ phosphor has a orthorhombic structure. The study suggested that Sm³⁺ doped phosphors are potential luminescence material for laser diode pumping and inorganic scintillators.     

Doppler-free high resolution spectroscopy of carbon disulphide and the effects of a magnetic field

A single-mode autoscan laser spectrometer operating in the ultraviolet in combination with a collimated molecular beam was used to measure high resolution fluorescence excitation spectra of the CS₂ V ¹B₂ ← X ¹Σ⁺ _g transition under collision-free conditions, and the effects of a magnetic field were measured. Rotational and vibrational levels were fully resolved, and Zeeman splittings were observed in many of the perturbed lines. The Zeeman interaction was observed to induce new perturbation, which induces new transitions, level splitting, and energy shift. When the magnetic field strength was changed, the magnitude of the interaction, which was observed in the absence of a magnetic field, changed dramatically depending on the energy shifts of the Zeeman components. It is shown that the V ¹B₂(¹Δ_u) state is mixed with the B₂(³A₂) component by first-order spin-orbit interaction, and through the mixed component, the Zeeman interaction between the V ¹B₂(¹Δ_u) and ³A₂(³Δ_u) states is induced. Large Zeeman splittings were observed for most of the background lines of weak intensity, and this demonstrates that the background levels are levels of the ³A₂(³Δ_u) state. The fluorescence decays of single Zeeman components were observed to be single exponential. The lifetimes of the perturbing ³A₂(³Δ_u) levels were determined by deperturbation analysis. Triplet-triplet ³A₂(³Δ_u) → ³B₂(³Σ⁺ _u) emission was confirmed. It was demonstrated that the quenching of the V ¹B₂ → X ¹Σ⁺ _g fluorescence by a magnetic field was caused by mixing of the ³A₂ state with the V ¹B₂ state and the resulting increase of triplet-triplet emission. In a time-dependent picture, the intersystem crossing from the ¹B₂(¹Δ_u) and ³A₂(³Δ_u) states is enhanced by the magnetic field.     

Relaxation of excited states of Tm3+ and Tm3+-Eu3+ energy transfer in YVO4 crystal

Tm³⁺-Eu³⁺ energy transfer processes and relaxation dynamics of the ³ H ₄ and ³ F ₄ excited states of Tm³⁺ ions in 1 at. % Tm³⁺, 5 at. % Eu³⁺:YVO₄ single crystal were studied. Contribution of Tm³⁺-Eu³⁺ energy transfer reduces effectively the lifetime of terminal level in a potential ³ H ₄–³ F ₄ laser transition at around 1.48 μm. Adverse quenching of the ³ H ₄ emission by Eu³⁺ ions is found to be less efficient than that reported for Tm³⁺ + Tb³⁺ system in YVO₄. The classical Inokuti–Hirayama model accounts well for an experimental decay curve of the ³ H ₄ emission recorded for co-doped crystal. Stimulated emission cross section for ³ H ₄–³ F ₄ transition of Tm³⁺ at around 1.48 μm was analyzed taking into account the anisotropy of YVO₄ crystal. PACS 42.55.Xi; 42.62.Fi     

Porous sulfated metal oxide SO<Subscript>4</Subscript><Superscript>2−</Superscript>/Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> as an anode material for Li-ion batteries with enhanced electrochemical performance

Sulfated metal oxide SO₄ ^2?/Fe₂O₃ was prepared by a novel facile sol–gel method combined with a subsequent heating treatment process. The as-synthesized products were analyzed by XRD, FTIR, and FE-SEM. Compared with the unsulfated Fe₂O₃, the agglomeration of particles has been alleviated after the incorporation of SO₄ ^2?. Interestingly, the primary particle size of the SO₄ ^2?/Fe₂O₃ (about 5 nm) is similar to its normal counterparts even after the calcination treatment. More importantly, SO₄ ^2?/Fe₂O₃ exhibits a porous architecture, which is an intriguing feature for electrode materials. When used as anode materials in Li-ion batteries, SO₄ ^2?/Fe₂O₃ delivered a higher reversible discharge capacity (992 mAh g^?1), with smaller charge transfer resistance, excellent rate performance, and better cycling stability than normal Fe₂O₃. We believed that the presence of SO₄ ^2? and porous architecture should be responsible for the enhanced electrochemical performance, which could provide more continuous and accessible conductive paths for Li⁺ and electrons.     

Tetragonal distortions of the octahedral environments of Cr3+, Fe3+ and Gd3+ ions in A2CdF4 (A = Rb,Cs) and ACdF3 crystals

Abstract

The tetragonal distortions of local octahedral environments of Cr³⁺, Fe³⁺ and Gd³⁺ ions in Rb₂CdF₄, Cs₂CdF₄, RbCdF₃ and CsCdF₃ crystals have been studied by analyzing their EPR spectra. From the studies, it is found that the tetragonal distortions for Cr³⁺ and Fe³⁺ impurity ions, which substitute Cd²⁺ and have nearly the same ionic radius, are close to each other, whereas that for Gd³⁺ impurity ion, having a larger ionic radius, is larger than those for Cr³⁺ and Fe³⁺ ions in the same crystal. It appears that not only the impurity-ligand distance, but also the tetragonal distortions of impurity centres in crystals are closely related to the size of impurity.     

From optical spectroscopy to a concentration quenching model and a theoretical approach to laser optimization for Yb3+-doped YLiF4 crystals

A spectroscopic characterization was carried out to identify crystal-field levels for magnetic-dipole transitions of Yb³⁺ ions located in the Y³⁺ dodecahedral S₄ crystallographic site in YLiF₄ (YLF) crystals which were grown either by the Czochralski technique or by the laser heated pedestal growth (LHPG) technique. The concentration dependence of the measured decay time of the ²F_5/2 excited level of Yb³⁺ was analysed in order to understand relevant concentration quenching mechanisms. Under Yb³⁺ ion infrared pumping, self-trapping and up-conversion non-radiative energy transfer to trace rare-earth impurities (Er³⁺, Tm³⁺) has been observed over the visible region and interpreted by a limited-diffusion process within the Yb³⁺ doping ion subsystem to the impurities. The principal parameters useful for a theoretical approach for potential laser applications of Yb³⁺-doped YLiF₄ crystals have also been given.     

89Yttrium nuclear magnetic resonance studies

With a Fourier-transform spectrometer, especially developed for nuclei with weak NMR signals, the lines of⁸⁹Y have been investigated in aqueous solutions of Y(NO₃)₃, YCl₃, and Y(ClO₄)₃. The concentration dependence of the chemical shifts of the⁸⁹Y resonance frequencies in these solutions were measured. Using this dependence, the Larmor frequency of the⁸⁹Y³⁺ ion solely surrounded by water was determined by extrapolation. The Larmor frequency of⁸⁹Y was referred to those of²H,³⁹K, and⁷³Ge with high accuracy. The magnetic moment of the⁸⁹Y³⁺ ion purely surrounded by H₂O molecules is μ(⁸⁹Y³⁺) = ?0.1368523(4) μ_N. The concentration dependence of Y(NO₃)₃ solutions in D₂O yields the solvent isotope effect δ(⁸⁹Y³⁺ in D₂O)?δ(⁸⁹Y³⁺ in H₂O)= ?(4.3±0.5)ppm. The⁸⁹Y relaxation times T₁ and T₂ of a 3 molal aqueous Y(NO₃)₃ solution were determined in the pH range ?0.5...+1.25. T₁ 190...90 s is nearly constant in this range, whereas the transverse relaxation rate T₂ ^?1 increases strongly with increasing pH; this effect seems to be due to the chemical exchange of the hydrated Y³⁺ ion between a monomer and a polymer site.     

The luminescence of bismuth and europium in Ca4YO(BO3)3

A series of Bi³⁺/Eu³⁺ singly and doubly activated Ca₄YO(BO₃)₃ phosphors were synthesized by solid-state reaction method. The structures and photoluminescent properties of the phosphors were investigated at room temperature. Under UV excitation Bi³⁺ and Eu³⁺ show a high light output. Ca₄YO(BO₃)₃:Eu³⁺ has potential application as a phosphor for fluorescent lamps. The luminescence of Bi³⁺ and Eu³⁺ in Ca₄YO(BO₃)₃ resembles more that in the rare earth oxides than that in borates. The free oxygen ion in the host lattice, which is not bonded to any boron ions seems to be responsible for that. In this host lattice energy migration between linear Eu³⁺ chains occurs. The emission of Bi³⁺ is completely quenched when Eu³⁺ is co-doped. A model was proposed to explain it.     

He-Ne Laser for Intra-Cavity Enhanced Absorption Measurement

It has been shown recently that when a relatively weak absorber is placed within a laser cavity an enhacement of absorption occurs^1–3. This method has been succesfully used for trace analysis of Na^1,4, I₂ ^3,5, Sr and Ba^{+ 6}, Eu(NO₃)₃ ^2,8, Pr(NO₃)₃, NdCl₃ and HoCl₃.⁸ In these experiments the absorbing species were placed inside the cavity of: flashlamp-pumped dye lasers^1–4,6 continous wave dye lasers^3,5 and dye lasers pumped by a ruby laser⁸.     

CaCuMn<Subscript>6</Subscript>O<Subscript>12</Subscript> vs. CaCu<Subscript>2</Subscript>Mn<Subscript>5</Subscript>O<Subscript>12</Subscript>: A comparative study

The ferrimagnetic compounds Ca(Cu_xMn_3?x)Mn₄O₁₂ of the double distorted perovskites AC₃B₄O₁₂ family exhibit a rapid increase of the ferromagnetic component in magnetization at partial substitution of square coordinated (Mn³⁺)_C for (Cu²⁺)_C. In the transport properties, this is seen as a change of the semiconducting type of resistivity for the metallic one. The evolution of magnetic properties of Ca(Cu_xMn_3?x)Mn₄O₁₂ is driven by strong antiferromagnetic exchange interaction of (Cu²⁺)_C with (Mn³⁺/Mn⁴⁺)_B coordinated octahedra. The competing interactions of (Mn³⁺)_C with (Mn³⁺/Mn⁴⁺)_B lead to the formation of noncollinear magnetic structures that can be aligned by magnetic fields.     

Up-conversion emissions of Er<Superscript>3+</Superscript>-Yb<Superscript>3+</Superscript> codoped Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles by the arc discharge synthesis method

The Er³⁺-Yb³⁺ codoped Al₂O₃ nanoparticles with an average particle size of about 50 nm have been synthesized by an arc discharge synthesis method. The green and red up-conversion emissions centered at about 526, 547 and 677 nm, corresponding respectively to the ²H_11/2→⁴I_15/2, ⁴S_3/2→⁴I_15/2 and ⁴F_9/2→⁴I_15/2 transitions of Er³⁺, were detected by a 978-nm semiconductor laser diode excitation. The Annealing has evident effect on the up-conversion emissions of the samples: The red up-conversion emission is noticeable before annealing; however, the green up-conversion emission becomes predominant after annealing. The mixture of (Er,Yb)₃Al₅O₁₂ and α-(Al,Er,Yb)₂O₃ phases is more favorable for green up-conversion emissions due to an enhancement of the ESA (I) of ⁴I_11/2+a photon→⁴F_7/2 and ET (III) of ²F_5/2(Yb³⁺)+⁴I_11/2(Er³⁺)→²F_7/2(Yb³⁺)+⁴F_7/2(Er³⁺) processes. The two-photon absorption up-conversion process is involved in the green and red up-conversion emissions. The results have proved that arc discharge synthesis is a new promising preparation technology for optical materials. Supported by National Natural Science Foundation of China (Grant No. 10804015), the Scientific Research Foundation for Doctor of Liaoning Province (Grant No. 20071095), and the Educational Committee Foundation of Liaoning Province (Grant No. 2008123)     

Synthesis, luminescence and crystallographic structure of Eu-doped garnet-type yafsoanite Ca3Te2(ZnO4)3

A red-emitting phosphor of Eu³⁺-doped calcium–tellurium–zinc oxide, Ca₃Te₂(ZnO₄)₃, with a garnet-type structure was synthesized by high temperature solid-state reactions. This phosphor exhibited a strong red emission. The photoluminescence excitation spectrum showed that Ca₃Te₂(ZnO₄)₃:Eu³⁺ can be effectively excited by UV–visible light. The property of long-wavelength excitation for this material has a benefit as a red phosphor in application of white light-emitting diodes. The colour coordinates were calculated. The excitation and emission spectra and luminescence decay curves were obtained using a pulsed, tunable, narrowband dye laser. Crystallographic sites and charge compensation mechanism of Eu³⁺ ions were discussed. The emission line from Eu³⁺ in intrinsic crystallographic site in the lattice was located at 579.56 nm. The emission line from Eu³⁺ in another disturbed site, which is created by the defects created by the charge-compensation, was located at 580.88 nm. The disordered crystallographic sites of Eu³⁺ are benefit for their strong red luminescence corresponding to the ⁵D₀→⁷F₂ transition.