Citric Acid Complex Sol-Gel Method to Prepare Lu2SiO5:Eu Phosphor

The Lu2SiO5 dried gel was prepared by the sol-gel reaction followed by a 24h drying at 90°C.The thermogravimetry–differential scanning calorimetry (TG-DSC) analysis curves of the dried gel demonstrates mass and enthalpy changes as temperature raised.The obtained dried gel was calcined at 900°C,1000°C,1100°Cand1200°C each for 2h to prepare polycrystalline Eu3+-dropped Lu2SiO5 phosphor.The phase composition and crystal structure was identified with an X-ray diffractometer (XRD).The dried gel was crystallized into A-type LSO phase at 1000°C, and transferred to B-type LSO phase when temperature was raised above 1050°C.The obtained LSO grain size is 200-300nm revealed in Field-emission scanning electron microscopy (FE-SEM) images.The photoluminescence spectrum of the obtained 2mol% Eu3+-dropped Lu2SiO5 phosphor showed a broad excitation band around 263nm and a sharp emission peak at 613nm.

Effects of Ti4+ Ions on Fluorescence Properties of Sr2CeO4:Sm3+ Phosphors

Ti4+-doped Sr2CeO4:Sm3+ phosphors were synthesized with the solid-state reaction method and the effects of doping Ti4+ on the photoluminescence properties were investigated in detail. A broad excitation band ascribed to the O2-–Ce4+ transition was observed in the range of 200 to 400 nm and with doping Ti4+ into Ce4+ sites, the intensity of charge transfer band of O2- →Ce4+ (300–370 nm) was significantly broaden and enhanced. As a result, the emission intensity of Sr2Ce1−xTixO4 has improved about 85% by doping 0.01 mol Ti4+. White emission of −Sr2-yCe0.99Ti0.01O4:ySm3+ at y ≤ 0.03 is due the co-existence of Ce4+ → O2- CT emission and 4G5/2–6HJ Sm3+ transitions whereas only the Sm3+ red emission prevails for 003<y≤0.15. The Sr1.99Ce0.99Ti0.01O4:0.01Sm3+ phosphor exhibited excellent color purity. Its chromaticity coordinate is measured to be (0.326, 0.322), which is close to the pure white (0.33, 0.33). The results showed that Sr1.99Ce0.99Ti0.01O4: 0.01Sm3+ phosphors could be considered as a potential single-phase white-emitting phosphor for white light-emitting diodes.

Effects of the Sr/Si Ratio on the Photoluminescence Properties of Sr3SiO5:Eu2+ Nanophosphors

Sr3SiO5:Eu2+ nanophosphors for white LEDs were synthesized by solgel method. The crystalline phases were examined with X-ray diffraction (XRD). Luminescence properties were studied, and effects of the Sr/Si ratio on the emission spectra were also studied. The nanophosphor showed a broad excitation band from 300 to 500 nm and a broad band emission peaking at 593 nm due to the typical electron transition of Eu2+ 4f74f65d1. Remarkable enhancement in luminescence characteristics was observed when excesses silica was used. This phenomenon may be attributed to the improvement of Si sensitized the luminescence of Eu2+ in the Sr3SiO5 nanophosphor.

Luminescent Properties of Re2SiO4:Tm3+ (Re=Mg,Ba,Sr) Under VUV

New phosphors of Tm3+ doped Re2SiO4 (Re=Mg, Ba, Sr) were prepared by the solid-state reaction and their luminescent properties were investigated. X-ray powder diffraction analysis confirmed the formation of Re2SiO4: Tm3+ (Re=Mg, Ba, Sr). The excitation spectra indicated that this phosphor can be effectively excited by 161nm. It consists of peaked at 175nm and a broad excitation band from 184nm to 300nm, corresponded to the absorption of the host lattice and the O−Tm3+ charge transfer transitions. The emission peaks at about 357nm, 459nm, 485nm is separately corresponds to the 1D2 → 3H6, 1D2 → 3H4, 1G4 → 3H6 transitions of Tm3+. As the radius of alkali earth ion in Re site increases, the main emission peaks changed to 478nm from 459nm.

Divalent and Trivalent Europium Doped Alumina Waveguides Elaborated by Pulsed Laser Deposition

ABSTRACTEuropium doped alumina Al2O3optical waveguides were prepared by pulsed laser deposition (PLD) using a KrF laser. The targets were obtained by sintering doped powders synthesized by a sol-gel method. Depending on the oxygen pressure used during the deposition, Eu3+ (for 0.1 mbar) or Eu2+ (for 10−5 mbar) are obtained in the films. Two kinds of Eu2+ ions are present, with a 4f-5d broad excitation band peaking at 330 nm and emission bands located at 490 nm or 585 nm respectively. For Eu3+ doped films, the usual 5D0 to the 7FJ multiplets emission spectra were observed. The emission lines are strongly inhomogeneously broadened. Low temperature site selective fluorescence measurements were achieved in order to correlate the different Eu3+ sites observed with the structure of the films (amorphous or γ crystallized).

Photoluminescence Excitation Spectroscopy of Carbon-Doped Gallium Nitride

We have done a comparative study of carbon-doped GaN and undoped GaN utilizing photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopies in order to investigate deep levels involved in yellow luminescence (YL) and red luminescence (RL). When the GaN was excited by above-bandgap light, red luminescence (RL) centered at 1.82 eV was the dominant below-gap PL from undoped GaN, but carbon-doped GaN below-gap PL was dominated by yellow luminescence (YL) centered at 2.2 eV. When exciting PL below the band-gap with 2.4 eV light, undoped GaN had a RL peak centered at 1.5 eV and carbon-doped GaN had a RL peak centered at 1.65 eV. PLE spectra of carbon-doped GaN, detecting at 1.56 eV, exhibited a strong, broad excitation band extending from about 2.1 to 2.8 eV with an unusual shape that may be due to two or more overlapping excitation bands. This RL PLE band was not observed in undoped GaN. We also demonstrate that PL spectra excited by below gap light in GaN films on sapphire substrates are readily contaminated by 1.6−1.8 eV and 2.1−2.5 eV chromium-related emission from the substrate. A complete characterization of the Cr emission and excitation bands for sapphire substrates enables the determination of the excitation and detection wavelengths required to obtain GaN PL and PLE spectra that are free of contributions from substrate emission.