Intense blue-emitting Ca5Al8O14: Eu phosphor for mercury free lamp

The calcium aluminates doped with Eu ions, Ca₅Al₈O₁₄: Eu, phosphors are prepared by the combustion method. The formation of crystalline aluminates was confirmed by X-ray diffraction pattern. The prepared phosphors were characterized by SEM, TGA, DTA, particle size analyzer and Photoluminescence (PL) techniques. From the UV-excited luminescence spectra it was found that the Eu ions acts as a luminescent centre with luminescence at the blue (λ _max = 470 nm) region due to 4f ⁶5d ¹ → 4f ⁷ transition. The excitation spectra show the broad band at 355 nm wavelength (λ _em = 470 nm). The excitation 355 nm is a mercury free excitation and therefore Ca₅Al₈O₁₄: Eu may be useful for the solid state lighting phosphor in lamp industry.      

Luminescence of CaGa<Subscript>2</Subscript>Se<Subscript>4</Subscript>:Eu crystals

We have studied photoluminescence and thermoluminescence (PL and TL) in CaGa₂Se₄:Eu crystals in the temperature range 77–400 K. We have established that broadband photoluminescence with maximum at 571 nm is due to intracenter transitions 4f⁶ 5d–4f⁷ (⁸S_7/2) of the Eu²⁺ ions. From the temperature dependence of the intensity (log I–10³/T), we determined the activation energy (E _a = 0.04 eV) for thermal quenching of photoluminescence. From the thermoluminescence spectra, we determined the trap depths: 0.31, 0.44, 0.53, 0.59 eV. The lifetime of the excited state 4f6 5d of the Eu²⁺ ions in the CaGa₂Se₄ crystal found from the luminescence decay kinetics is 3.8 μsec. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 1, pp. 112–116, January–February, 2009.     

The study of two-color excitation upconversion of Pr(0.5)Yb(3):ZBLAN

The excited state absorption upconversion of Pr(0.5)Yb(3):ZBLAN glass material, under two-color excitation of the 960 nm semiconductor laser and the Xe lamp light simultaneously, is reported in this article. It was found that the upconversion emission spectra of 480.1, 519.0, 601.9 and 631.8 nm coincide with the common emission spectra. Meanwhile, the upconversion-excitation spectrum has three obvious peaks under two-color excitation, and they respectively correspond to the 856.0 nm upconversion excitation transition [¹G₄(Pr³⁺)→¹I₆(Pr³⁺) and ¹G₄(Pr³⁺)→³P₁(Pr³⁺)], the 789.0 nm upconversion excitation transition ¹G₄(Pr³⁺)→³P₂(Pr³⁺), and the 803.7 nm upconversion excitation transition ³H₆(Pr³⁺)→¹D₂(Pr³⁺). The upconversion excitation transition ¹G₄(Pr³⁺)→¹I₆(Pr³⁺) is strong because its oscillator strength f = 23.040×10⁻⁶ is large, which results in a large peak appearing in the upconversion excitation spectrum. That is just the new interesting two-color excitation upconversion luminescence phenomenon of Pr(0.5)Yb(3):ZBLAN induced by one laser and one continuous normal light simultaneously.     

Synthesis and Fluorescence Properties of Lanthanide (III) Perchlorate Complexes with Naphthyl-Naphthalinesulphonylpropyl Sulfoxide

A ligand with double sulfinyl groups, naphthyl-naphthalinesulphonylpropyl sulfoxide(dinaphthyl disulfoxide, L), was synthesized by a new method and its several lanthanide (III) complexes were synthesized and characterized by element analysis, molar conductivity, coordination titration analysis, IR, TG-DTA, ¹HNMR and UV spectra. The composition of these complexes, were RE₂(ClO₄)₆·(L)₅·nH₂O (RE = La, Nd, Eu, Tb, Yb, n = 2 ∼ 6, L = C₁₀H₇SOC₃H₆SOC₁₀H₇). The fluorescent spectra illustrated that the Eu (III) complex had an excellent luminescence. It was supposed that the ligand was benefited for transferring the energy from ligand to the excitation state energy level (⁵D₀) of Eu (III). The Tb (III) complex displayed weak luminescence, which attributed to low energy transferring efficiency between the average triplet state energy level of ligand and the excited state (⁵D₄) of Tb (III). So the Eu (III) complex displayed a good antenna effect for luminescence. The phosphorescence spectra and the relationship between fluorescence lifetime and fluorescence intensity were also discussed.     

Fluorescence of N,N-di(2-carboxyethyl)-<Emphasis Type="Italic">p</Emphasis>-anisidine in solution and crystalline states

The fluorescence properties of N,N-di(2-carboxyethyl)-p-anisidine (I) in solvents of various nature and in the crystalline state have been studied at room temperature (273 K) and at the boiling point of liquid nitrogen (77 K). Fluorescence in aqueous solutions of I with protonated (λ _ex /λ _fl ^max = 225/290 nm) and unprotonated (λ _ex /λ _fl ^max = 270/380 nm) amino nitrogen has been detected. On going from aqueous solutions to nonaqueous, the fluorescence band of unprotonated I experiences a blue shift and its intensity rises. The fluorescence intensity of the band in aprotic polar solvents is higher than that in protic solvents. A linear dependence of the fluorescence intensity of deprotonated I on Cu(II) concentration (ranging from 1.0 to 5.0 mg/dm³) in aqueous solution has been found. The fluorescence intensity of I in aqueous solutions at 77 K and pH 1–6 has been shown to increase in the presence of Zn(II) (1–170 mg/dm³) and Cd(II) (2–330 mg/dm³) although a similar dependence is not observed at 293 K.     

Spontaneous and stimulated red luminescence of Lu2O3: Eu nanocrystals

The spectra of spontaneous and stimulated luminescence of Lu₂O₃: Eu (7 at %) nanopowders at different optical pumping intensities have been investigated. The obtained results—changes in the shape of the red luminescence spectra and in the lifetime of the ⁵ D ₀ excited state of Eu³⁺ ions—indicate the onset of superluminescence with an increase in the excitation power. It has been found that an increase in the optical pumping intensity leads to a decrease in the luminescence decay time of the Lu₂O₃: Eu (7 at %) phosphor in the stimulated luminescence regime and to an increase in the quantum efficiency of red luminescence with a maximum at 611 nm.     

Emission analysis of RE3+ (Eu3+, Tb3+ & Ho3+): B2O3-BaO-LiF/AIF3 glasses

We report here the luminescence spectra of certain rare earth ions (Eu³⁺, Tb³⁺ & Ho³⁺) doped B₂O₃-BaO-LiF/AiF₃ based on the measurements of emission and decay curves of prominent emission transitions. For both the reference host glasses, FTIR, XRD, DTA-TG profiles have been recorded to understand their structural and thermal properties. Eu³⁺ doped glasses have shown five emission transitions of ⁵D₀ → ⁷F_{01,2,3 & 4} located at 580nm, 593nm, 615nm, 655nm and 704nm respectively with an excitation at λ_exci = 392 nm (⁷F₀ → ⁵L₆). Also under an UV source, these europium glasses have displayed a bright red emission from their surfaces. Tb³⁺ glasses have exhibited four emission bands of ⁵D₄ → ⁷F_6,5,4,3 at 491nm, 547nm, 588nm and 625nm respectively with an excitation at λ_exci = 376 nm (⁷F₆ → ⁵G₆). Intense green emission from the glass surfaces has been noticed upon exposure to the UV source. Prominently bluish-green emission has been noticed from the surfaces of the holmium glasses under an UV source and same emission transition (⁵F₄ → ⁵I₈) at 519 nm with an excitation at λ_exci = 389 nm (⁵I₈ − ⁵G₄) has also been obtained from their measured emission spectra. For all the prominent emissions of the rare earth glasses, decay curves have been measured to compute their lifetimes.     

Optical probing of Eu ions confined in an RF trap

The Eu ions confined in an RF quadrupole trap, has been optically detected. Using a tunable dye laser which is pumped by a Nd-YAG pulsed laser system, the resonance ⁹S₄^9S_4–6p _3/2, J = 5 transition of the Eu ions have been excited and the resulting fluorescence to the metastable ⁹D_4-6^9D_{4-6} state has been detected. In preparation to determine the ground-state hyperfine splitting of the odd isotopes we found the optimum trapping operating point. We have also observed a number of instabilities inside the region of the stability for an ideal trap. These non-linear resonances arise from higher-order contributions to the ideal quadrupole potential.     

Characterization and photoluminescence studies of Eu<Superscript>2+</Superscript>-doped BaSO<Subscript>4</Subscript> phosphor prepared by the recrystallization method

Eu doped BaSO₄ was prepared by the recrystallization method and characterization of the material was done by using X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR) techniques. From the XRD pattern of Eu doped BaSO₄ compound, it was found that the prominent phase formed was BaSO₄ and traces of other phases were very weak and the result of FTIR spectrum of BaSO₄:Eu shows that the sulfur-oxygen stretch was found at around 1100 cm⁻¹. The room-temperature PL spectra of the Eu doped BaSO₄ sample showed one peak centered at 374 nm, which is the characteristic emission of Eu²⁺ ion. This emission band at 374 nm corresponds to the 4f⁶ 5d→4f⁷ (⁸S_7/2) transitions of Eu²⁺ ions. The excitation spectrum taken at the wavelength 374 nm extends over a wide range of wavelengths from 220–350 nm with a strong peak at around 260 nm. Furthermore, the present sample shows good crystal quality and high photoluminescence sensitivity. Hence our results suggest possible potential applications of Eu doped BaSO₄ phosphor in optoelectronic devices.     

The nature of the effect of Gd(III) on fluorescence of Ln(III) chelates in water solutions

The intensity of fluorescence of Eu(III) and Sm(III) ions sensitized by molecules of n-benzoyltrifluoroacetone and 1,10-phenanthroline introduced in a water solution in a ratio of 3: 1 is studied as a function of the ion concentration in the solution. The comparison of the fluorescence decay curves of Eu(III) and Sm(III) in D₂O and H₂O (pH≥7) solutions containing 10^?4 M of n-Cl-BTFA and 3×10^?5 M of 1,10-phen and the values of τ_fl of Sm(III) in themselves (51–90 μs) are indicative of an insignificant content of water molecules in the first coordination sphere of ions. The effect of other ions on I _fl and τ_fl of Eu(III) ions is studied under these conditions. The intensity of fluorescence of Eu(III) in solutions of 10^?4 M Cl-BTFA and 3×10^?5 H 1,10-phen is found to increase by 1–2 orders of magnitude in the presence of Y(III) and Gd(III) ions, and the magnitude of this effect is unaffected by deoxygenation of the solution. The introduction of a third ion Nd(III) in the solution is shown to attenuate the influence of Gd(III) on I _fl of Eu(III) for Nd(III) concentrations commensurable with the Eu(III) concentration in the solution. The strength of the influence of Gd(III) ions on I _fl of Eu(III) is found to depend on the method of preparation of the solution. The analysis of the results obtained testifies that inhomogeneities consisting of chelates of lanthanide ions displaced from the water structure appear in water. The presence of these inhomogeneities results in efficient energy transfer from ligands of Gd(III) chelates to Eu(III) chelates, which is the reason for the increasing I _fl of Eu(III). The possibility of using data on the enhancement of I _fl of Eu(III) in the presence of Gd(III) and on the reduction of τ_fl of Eu(III) in the presence of Nd(III) for estimating dimensions and structures of displaced systems is discussed.     

D?→Dπ and D?→Dγ decays: axial coupling and magnetic moment of D? meson

The axial coupling and the magnetic moment of D ^∗-meson or, more specifically, the couplings g_D^*Dpg_{D^{\ast}D\pi} and g_D^*Dgg_{D^{\ast}D\gamma }, encode the non-perturbative QCD effects describing the decays D ^∗→Dπ and D ^∗→Dγ. We compute these quantities by means of lattice QCD with N _f=2 dynamical quarks, by employing the Wilson (“clover”) action. On our finer lattice (a≈0.065 fm) we obtain g_D^*Dp⁺=20±2g_{D^{\ast}D\pi^{+}}=20\pm2, and g_{D^*0 D⁰g}=2.0±0.6 GeV^-1g_{D^{\ast0} D^{0}\gamma}=2.0\pm 0.6~{\rm GeV}^{-1}. This is the first determination of g_{D^*0 D⁰g}g_{D^{\ast0} D^{0}\gamma} on the lattice. We also provide a short phenomenological discussion and the comparison of our result with experiment and with the results quoted in the literature.     

Photo- and radio-excited luminescence properties of Eu-doped La2O3–Al2O3 based eutectics

Eutectic crystal of 0.5% Eu-doped 30LaAlO₃–70Al₂O₃ (vol %) was prepared by micro-pulling down (μ-PD) technique under nitrogen atmosphere. Being excited at a wavelength of 320 nm, the crystal exhibited intense emission band with a maximum at 450 nm which is corresponding to 4f⁶5d-4f⁷(⁸S_7/2) transitions of Eu²⁺. The decay time and fluorescence quantum efficiency (QE) were determined to be about 475 ns and 60%, respectively. When alpha-ray excited the crystal, both Eu²⁺ 4f⁶5d-4f⁷(⁸S_7/2) and Eu³⁺ 4f⁶-4f⁶ (⁵D₀-⁷F_1,2) emission peaks were observed at 435 nm and 600 nm. By the pulse height spectra, the relative scintillation light yield of the crystal was about 4% compared with that of BGO commercial scintillator.     

Fluorescence properties of divalent and trivalent europium ions in CdWO4 single crystals grown by Bridgman method

Optical absorption, excitation, and fluorescence were investigated in Eu ion-doped CdWO₄ single crystal grown by a modified Bridgman method. The results indicate that Eu²⁺ and Eu³⁺ ions coexist in CdWO₄ crystal and an energy transfer occurs between these Eu²⁺ and Eu³⁺ ions. When the crystal is excited by 266-nm light, the energy corresponding to the 4f⁶5d to ⁸S_7/2 transition of Eu²⁺ ions results in the excitation of the Eu³⁺ ions to the ⁵D_J level. The effect on fluorescence of annealing in oxygen at various temperatures was investigated. The excitation intensity of Eu²⁺ ions at 266 nm decreases as annealing temperature increases from 300 K to 1073 K, but it remains at a certain equilibrium level when the annealing temperature is further increased.     

Cooperative downconversion and near-infrared luminescence of Tb<Superscript>3+</Superscript>–Yb<Superscript>3+</Superscript> codoped lanthanum borogermanate glasses

In the present paper, we investigate the near-infrared (NIR) luminescence of Tb³⁺–Yb³⁺ codoped lanthanum borogermanate (LBG) glasses under visible and ultraviolet light excitation. The results indicate that NIR quantum cutting occurs through cooperative energy transfer from Tb³⁺ to Yb³⁺ ions when only 4f ⁸ levels of Tb³⁺ ions are excited in the wavelength region of 300–490 nm. The highest quantum efficiency under the excitation ⁵ D ₄ level of Tb³⁺ at 484 nm is 146%. Ultraviolet excitation that populates the charge transfer band (CTB) of Yb³⁺ near 270 nm does not result in quantum cutting as the fast nonradiative decay from CTB to ² F _5/2 level dominates. These materials are expected to be used as a converting layer for silicon solar cells to enhance their efficiency by splitting each high-energy photon into two NIR photons.     

White-light emission from Li<Subscript>2</Subscript>Sr<Subscript>1−3<Emphasis Type="Italic">x</Emphasis>/2</Subscript>Dy<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>SiO<Subscript>4</Subscript> phosphors

Li₂Sr_1−3x/2Dy _x SiO₄ phosphors were synthesized at 900°C in the normal atmosphere by a solid-state method. The synthesized phosphors were characterized by X-ray powder diffraction (XRD) and photoluminescence (PL) spectra. The photoluminescence excitation (PLE) spectra show excitation peaks ranging from 300 to 400 nm due to the 4f-4f transitions of Dy³⁺. This mercury-free excitation is useful for solid-state lighting and light-emitting diodes (LEDs). The predominant emission of Dy³⁺ ions under 349 nm excitation is observed at 479 nm (blue) due to the ⁴F_9/2→⁶H_15/2 transitions and 572 nm (yellow) due to ⁴F_9/2→⁶H_13/2 transitions, respectively. The PL results reveal that the optimal concentration of the Dy³⁺ ions in Li₂Sr_1−3x/2Dy _x SiO₄ phosphors is x=0.03 mol. The nature of the resonance energy transfer for the Dy³⁺ ions is confirmed by Huang’s rule. Simulation of the white light excited by 349 nm near-ultraviolet (n-UV) light is also performed for its potential for white LEDs.     

Solvent Effect on Absorption and Fluorescence Spectra of Three Biologically Active Carboxamides (C<Subscript>1</Subscript>, C<Subscript>2</Subscript> and C<Subscript>3</Subscript>). Estimation of Ground and Excited State Dipole Moment from Solvatochromic Method Using Solvent Polarity Parameters

The absorption and fluorescence spectra of three Carboxamides namely (E)-2-(4-Chlorobenzylideneamino)-N-(2-chlorophenyl)-4, 5, 6, 7-tetrahydrobenzo[b]thiophene-3-carboxamide (C₁), (E)-N-(3-Chlorophenyl)-2-(3, 4-dimethoxybenzylideneamino)-4, 5, 6, 7-tetrahydrobenzo[b]thiophene-3-carboxamide (C₂) and (E)-N-(3-Chlorophenyl)-2-(3, 4, 5-trimethoxybenzylideneamino)-4, 5, 6, 7-tetrahydrobenzo[b]thiophene-3-carboxamide (C₃) have been recorded at room temperature in solvents of different polarities using dielectric constant (ε) and refractive index (n). Experimental ground (μ_g) and excited (μ_e) state dipole moments are estimated by means of solvatochromic shift method and also the excited dipole moments are estimated in combination with ground state dipole moments. It was estimated that dipole moments of the excited state were higher than those of the ground state of all three molecules. Further, the changes in dipole moment (Dm \Delta \mu ) were calculated both from solvatochromic shift method and on the basis of microscopic empirical solvent polarity parameter (E_T^N E_T^N ) and the values are compared.     

Erbium electroluminescence excitation in amorphous hydrogenated silicon under thermally stimulated deep-center tunneling ionization

A study of the electroluminescence of erbium-doped, amorphous hydrogenated silicon, a-Si:H 〈Er〉, is reported. It has been found that the electroluminescence intensity at the wavelength λ=1.54 μm corresponding to the ⁴ I _13/2→⁴ I _15/2 intra-4f shell transition in Er passes through a maximum near room temperature. The unusual temperature and field dependences of the electroluminescence indicate electric-field induced multi-phonon tunneling emission of electrons from deep centers. The electroluminescence of Er³⁺ ions is due to their becoming excited as conduction-band electrons are captured by neutral dangling bonds (D ⁰ centers), which form when erbium is incorporated into the amorphous matrix. This Auger process transforms the center from its neutral state, D ⁰, to a negatively charged state, D ⁻, and the energy released in the capture is transferred by Coulomb interaction into the erbium-ion 4f shell. The steady-state current through the electroluminescent structure is supported by the reverse process of multi-phonon tunneling-electron emission from the D ⁻ center to the conduction band. The proposed theoretical model is in a good agreement with experimental data. Fiz. Tverd. Tela (St. Petersburg) 41, 210–217 (February 1999)     

Fast decay of high vibronic S1 states in gas-phase benzene

Lifetimes of different vibronic levels at high excess energies in the S₁ state of isolated benzene molecules are measured using for the first time a two-photon ionization pump–probe technique with UV femtosecond pulses. For the 6¹1³ state (3290 cm^-1 excess energy) at the onset of the ‘channel three’ a biexponential decay is found with a fast (τ_f=20 ps) and a slow (τ_s>500 ps) component. The values are in line with previous sub-Doppler high-resolution measurements of this band in our laboratory. We explain the measured faster decay (τ_f=900 fs, τ_s=100 ps) of the 7¹ state at a lower excess energy of 3077 cm^-1 by a simultaneous excitation of the adjacent 6¹ ₀1³ ₀16¹ ₁ hot band leading to a vibronic state of higher excess energy and faster decay. The vibronic levels 6¹1⁴ and 7¹1¹ at a higher excess energy of ≳4000 cm^-1 show a biexponential decay of τ_f=550 fs, τ_s=30 ps and τ_f≲300 fs, τ_s=20 ps, respectively. The experimental results point to dynamic processes within the vibronic level manifold of the S₁ state and a fast nonradiative electronic relaxation process. Received: 3 November 1999 / Published online: 5 July 2000     

Study of frequency upconversion in Yb<Superscript>3+</Superscript>/Eu<Superscript>3+</Superscript> by cooperative energy transfer in oxyfluoroborate glass matrix

Oxyfluoroborate glass co-doped with Eu and Yb ions has been prepared and characterized for its optical properties through photoluminescence, absorption and lifetime measurements. An intense red upconversion is observed from the ⁵D₀ level of Eu³⁺ ions through energy transfer from Yb³⁺ to Eu³⁺ ion when excited with 980 nm. The Judd–Ofelt parameters have been evaluated to estimate the local site symmetry around the Eu³⁺ ions. These parameters have been used to derive radiative properties such as transition probabilities, branching ratios, radiative lifetimes and stimulated emission cross-sections for the ⁵D₀–⁷F_J transitions. Decay of excitation of the ⁵D₀ level has been measured by monitoring the ⁵D₀→⁷F₂ transition (613 nm) at room temperature. Quantum efficiency for this transition is found to be 73%. We also monitored the effect of temperature on the fluorescence emission of Eu³⁺. PACS 42.70.Ce; 42.70.Hj