Shuanglong Yuan

Luminescence properties of Tb3+–Sm3+ codoped glasses for white light emitting diodes

Photoluminescence properties of silicate and borosilicate glasses codoped with Tb3+ and Sm3+ ions have been characterized by excitation and emission spectroscopies. When excited by ultraviolet light the glasses emit a combination of green and orange-red wavelengths giving white light. The ratio of the intensities of orange-red to green emissions can be tuned by varying both the concentration of the Sm3+ ion and an the composition of the glass matrix. The excitation and emission spectra show a self-quenching effect for the Sm3+ ions and an energy transfer from Tb3+ (D45) to Sm3+ (G5∕24).

Eu 2+ and Mn 2+ codoped Ba 2 Mg(BO 3 ) 2 —new red phosphor for white LEDs

A new red phosphor, Ba2Mg(BO3)2:Eu,Mn, was synthesized by the solid-state reaction method and its photoluminescence properties were investigated by excitation and emission spectra and decay curves. Its excitation band is extending from 250-450 nm, which is adaptable to the emission band of near-ultraviolet LED chips (350-420 nm). Upon the excitation of 365 nm light, the phosphor exhibits strong red emission centered at 615 nm. The relationship between Eu2+ and Mn2+ dopants was studied from the viewpoint of a crystal structure and by photoluminescence spectra and decay curves. The results show that the characteristic Eu2+ emission predominate in the emission band and Mn2+ promote the redistribution of Eu2+ at the cation sites of the host crystal.

Significant enhancement of visible up-conversion emissions of Y2O2S:Er3+ phosphors by Mn2+ sensitizing under 1550 nm excitation

A novel up-conversion (UC) emission route of Er3+ by Mn2+ sensitizing in a Y2O2S:Er3+ phosphor prepared via a high-temperature solid-state reaction method is reported here. This methodology resulted in a significant enhancement of visible up-conversion emission by 1550 nm laser diode excitation. By co-doping Mn2+, the visible (red and green) UC emission intensity, which is assigned to the transitions of 4F9/2 → 4I15/2 (670 nm), 4S3/2 → 4I15/2 (547 nm), 2H11/2 → 4I15/2 (528 nm) of Er3+, was 2 to 3 times higher than that of the Mn2+-free one. As the concentration of Mn2+ was increased, the visible UC emission intensity was enhanced and then reduced. The phosphor powders were well crystallized in a hexagonal shape with an average size of ca. 2 μm. Based on the results of the luminescence spectra, energy matching conditions and three-photon process dependence on excitation power, a possible UC mechanism is proposed. The proposed sensitizing route may lead to a promising step towards high-intensity UC emissions of rare-earth ion doped phosphors.

Controlled growth and up-conversion luminescence of Y2O2S : Er3+ phosphor with the addition of Bi2O3

By adding Bi2O3 in phosphor raw materials, fine particles (ca. 500 nm in diameter) have been synthesized for the first time in Y2O2S : Er3+via high-temperature solid-state reaction. The influence of Bi2O3 content on the crystal growth and up-conversion (UC) luminescence (excited at 1550 nm) of Y2O2S : Er3+ phosphors was investigated by varying the Bi2O3 concentration from 0 to 10.0 mol%. As Bi2O3 concentration was increased, the average particle size was increased and then decreased, and the uniformity of the particle size was descended and then enhanced. The size change of Bi2O3 doped Y2O2S : Er3+ phosphors can be well explained by the liquid phase sintering mechanism. Compared to the phosphors without containing any Bi2O3, UC luminescence intensity (excited at 1550 nm) of phosphors containing Bi2O3 decreased, but was still sufficiently strong to the naked eye.

Synthesis of highly emissive CdSe quantum dots by aqueous precipitation method

CdSe quantum dots (QDs) with high quantum yield (QY) up to 76.57% are synthesized using the aqueous precipitation method. With the control of SeSO32- concentration in Se precursor, the nucleation speed and concentration of CdSe QDs are increased. The mass of obtained Cd2+ and Se2+ in nanocrystal is measured by inductively coupled plasma atomic emission spectrometry (ICPAES). XRD and HRTEM are used to identify the crystal phase and morphology of the products which are pure CdSe crystals in the cubic zinc blende phase and uniformly dispersed in the solution with the size between 2nm and 2.3 nm. Results demonstrate that the emission wavelength of CdSe QDs is 500 nm∼560 nm along with the increased temperature 50°C ∼90°C and prolonged time 5 min∼25 min.

Three-photon-excited upconversion luminescence of niobium ions doped silicate glass by a femtosecond laser irradiation

We report on the bluish green upconversion luminescence of niobium ions doped silicate glass by a femtosecond laser irradiation. The dependence of the fluorescence intensity on the pump power density of laser indicates that the conversion of infrared irradiation to visible emission is dominated by three-photon excitation process. We suggest that the charge transfer from O(2-) to Nb(5+) can efficiently contribute to the bluish green emission. The results indicate that transition metal ions without d electrons play an important role in fields of optics when embedded into silicate glass matrix.

Luminescent properties of novel red-emitting phosphor: Gd 2 O 2 CN 2 :Eu 3+

Eu3+-doped Gd2O2CN2 was firstly synthesized by a classical solid-state reaction of Li2CO3, Eu2O3 and GdF3 under NH3 gas flow in the presence of graphite at low firing temperature. Powder X-ray diffraction (XRD) analysis indicated that Gd2O2CN2: Eu3+ crystallizes in a trigonal-type structure with space group P-3m1. Gd2O2CN2: Eu3+ shows a sharp red emission band peaking at 626 nm under excitation at 300 nm at room temperature. PL spectra indicates that Eu3+ doped Gd2O2CN2 samples emit the typical emission peaks at 614 nm and 626 nm originated from the hypersensitive electric dipole transition (5D0→7F2) of Eu3+ ions. The optimized doping concentration of Eu3+ ions was found to be 7.5 at. %, and the critical transfer distance was calculated to be 10.907 A.

Green Synthesized CdSe Quantum Dots Capped by 3-Mercaptopropionic Acid Sensitized Solar Cells

In this paper, the green synthesized CdSe quantum dots (QDs) capped by 3-mercaptopropionic acid (MPA) sensitized solar cells are fabricated. Glycerol is chosen as the solvent to prepare the CdSe QDs, which makes the whole reaction is environmental-friendly. After MPA ligand exchanging, the as-synthesized CdSe QDs maintain the original absorbance at ca. 500 nm, coherence to the maximum absorbance of the solar spectrum. The strong photoluminescence quenching of the MPA capped QDs increases the nonradiative decay processes and is beneficial to the electron transfer. Then the MPA ligand exchanged QDs were assembled onto mesoscopic TiO2 film to integrate into QD sensitized solar cells. The power conversion efficiency of the QD-sensitized solar cells reaches 0.12 % under sun illumination (AM 1.5, 100 mW cm−2) and relatively mechanism is discussed.