Nm In Excitation Spectra Research Articles

EDTA-mediated morphology and tunable optical properties of Eu3+-doped NaY(MoO4)2 phosphor

Uniform and well-crystallized NaY(MoO4)2: Eu3+ 3D hierarchical flower-like architectures self-assembled from different building blocks have been successfully synthesized by a facile ethylene diamine tetraacetic acid (EDTA)-mediated hydrothermal route. The crystalline phase, size, morphology, and down-conversion luminescence properties were systematically characterized using powder X-ray diffraction, field emission-scanning electron microscopy, photoluminescence (PL) and photoluminescent excitation spectra (PLE), respectively. It was found that the pH value in the initial solution was responsible for the crystal phase determination of final products. The experimental results showed that the amount of EDTA was a key parameter which not only determined their spacial arrangement, but also affected the down-conversion luminescence intensity of the final products. In PL spectrum, a prominent red emission was observed due to the hypersensitive 5D0 → 7F2 transition, and the optimum doping level of Eu3+ was 20 %. Two strongest lines at 396 and 467 nm in excitation spectra of these phosphors matched well with the two popular emissions from near ultraviolet and blue GaN-based LEDs, so they could be explored for an efficient red region for white light-emitting diodes.

Photoluminescence properties and analysis of spectral structure of R_2(MoO_4)_3:Eu^3+ (R=La,Gd) phosphors

The site-selective excitation and emission spectroscopy and luminescence decay (lifetime) have been investigated in the 5D0→7F0 region using a pulsed, tunable, and narrowband dye laser. We observed two crystallographic sites for Eu3+ in La2(MoO4)3 and one crystallographic site for Eu3+ in Gd2(MoO4)3. The stark energy levels for Eu3+ at different sites were assigned from site-selective emission spectra. The luminescent properties of the as-synthesized samples were also investigated, which showed strong lines at 395 nm in excitation spectra and intensive red emission, indicating that they could be used as red components for white LEDs.

Luminescent properties of Ba2ZnSi2O7:Eu3+phosphors prepared by sol-gel process

A novel red phosphor Ba 2 ZnSi 2 O 7 :Eu 3+ has been synthesized by sol-gel method. The crystallinity, particle size, morphology, chemical composition and luminescent properties were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), energy-dispersion spectrum (EDS) and spectrofluorometer, respectively. The results of thermogravimetric (TG) and XRD indicated that the Ba 2 ZnSi 2 O 7 :Eu 3+ phosphors crystallized completely at 900 °C. The luminescent properties of phosphor showed red emission is obtained by exciting at 394 and 465 nm which are owing to the sharp 7 F 0 5 L 6 and 7 F 0 5 D 2 lines of Eu 3+ . Two strongest lines at 394 and 465 nm in excitation spectra of the phosphor match well with the two popular emissions from near-ultraviolet (UV) and blue GaN-based light emitting diodes (LEDs), so it could be used as red components for white LEDs.

Hydrothermal synthesis and vacuum ultraviolet-excited luminescence properties of novel Dy 3+-doped LaPO 4 white light phosphors

Novel LaPO 4:Dy 3+ white light phosphors with monoclinic system were successfully synthesized by hydrothermal method at 240 °C. The strong absorption at around 147 nm in excitation spectrum was assigned to the host absorption which suggested that the vacuum ultraviolet-excited energy was efficiently transferred from the host to the Dy 3+ ion. The f–d transition of Dy 3+ ion was observed locating at 182 nm. Under 147 nm excitation, La 1− x PO 4: xDy 3+ phosphor exhibited two emission bands locating at 571 nm (yellow) and 478 nm (blue) which corresponded to the hypersensitive transitions 4F 9/2– 6H 13/2 and 4F 9/2– 6H 15/2. It was the two emission bands that lead to the white light.

Luminescent properties of R 2(MoO 4) 3:Eu 3+ (R=La, Y, Gd) phosphors prepared by sol–gel process

A series of red phosphors R 0.8Eu 1.2(MoO 4) 3 (R=La, Y, and Gd) have been synthesized by sol–gel method. The crystallization processes of the phosphor precursors were characterized by X-ray diffraction (XRD) and thermogravimetry–differential thermal analysis (TG–DTA), and the properties of these resulting phosphors have also been characterized by photoluminescence (PL) spectra and reflectance spectra. Field emission scanning electron microscopy (FE-SEM) was also used to characterize the shape and the size of the samples. The results of TG–DTA and XRD indicated that all of the R 0.8Eu 1.2(MoO 4) 3 (R=La, Y, and Gd) phosphors crystallized completely at 650 °C. Y 0.8Eu 1.2(MoO 4) 3 and Gd 0.8Eu 1.2(MoO 4) 3 have two structures, monoclinic and orthorhombic, while La 0.8Eu 1.2(MoO 4) 3 only adopts monoclinic structure. The luminescent properties of phosphors R 0.8Eu 1.2(MoO 4) 3 (R=La, Y, and Gd) are dependent on their structures to some extent. The orthorhombic Y 0.8Eu 1.2(MoO 4) 3 and Gd 0.8Eu 1.2(MoO 4) 3 phosphors show very similar luminescent properties, which differ from those of phosphors with monoclinic structure. For all of R 0.8Eu 1.2(MoO 4) 3 (R=La, Y, and Gd) phosphors, intense red emission is obtained by exciting at ∼394 and ∼465 nm which are owing to the sharp 7F 0→ 5L 6 and 7F 0→ 5D 2 lines of Eu 3+. Two strongest lines at 394 and 465 nm in excitation spectra of these phosphors match well with the two popular emissions from near-UV and blue GaN-based LEDs, so they could be used as red components for white light-emitting diodes.

The luminescence properties of Dy 3+-activated SrB 4O 7 under VUV excitation

Dy 3+-doped SrB 4O 7 phosphors were synthesized by solid-state reaction. The luminescence properties of white-light SrB 4O 7:Dy 3+ under vacuum ultraviolet (VUV) excitation were firstly investigated. According to strong absorption around 147 nm in excitation spectra, energy can easily be transferred to the energy levels of Dy 3+ from host absorption, and hence luminescence of SrB 4O 7:Dy 3+ under VUV excitation was effective, and it has the potential of being applied to a white lamp-house for mercury-free lamp.

Optical bioimaging: from living tissue to a single molecule: calcium imaging in blood vessel in situ employing two-photon excitation fluorescence microscopy.

Recent developments in optoelectronics permit real-time Ca(2+) imaging of thin planes within cells utilizing laser scanning confocal microscopy (LSCM). However, a major complication associated with this imaging system involves increased phototoxicity with improved spatiotemporal resolution. Two-photon excitation microscopy (TPEM) helps to minimize phototoxicity due to the restriction of this technique to the volume proximal to the geometric focus of the light. In this study, the capability of Ca(2+) imaging was investigated employing recently developed real-time TPEM, RTS2000MP (Bio-Rad, Tokyo) with a mode-locked Ti-sapphire laser. Z-axis resolution of RTS2000MP with high NA objectives defined as full-width at half maximum (FWHM) with a 0.5-microm fluorescent bead provided values nearly identical to those obtained with LSCM at a small pinhole (0.2 mm) (approximately 0.6 microm). When serial sectioning of 21 sequential images at 0.3-microm intervals in cultured endothelial cells loaded with calcein and tetramethyl-rhodamine methylester were performed with TPEM, the z-axis resolution was higher than that observed with LSCM; moreover, the photobleaching rate was significantly lower than that obtained with LSCM. Maximum fluorescence intensities were detected at 780 nm in excitation spectra of fluo-3 and fluo-4 Ca(2+)-sensitive probes with TPEM. Fluorescence images in mouse arterial endothelial cells loaded with fluo-4 could be clearly visualized by TPEM in situ. Application of acetylcholine caused oscillatory increase in [Ca(2+)](i) of endothelial cells; subsequently, relaxation along the major axis of smooth muscle cells was evident. Furthermore, consecutive long-lasting experiments could be repeated with identical response in the same microscopic field. In conclusion, fluorescence imaging employing TPEM is useful for Ca(2+) imaging in blood vessels in situ.