Pressure behavior of deep centers in ZnSxTe1-x alloys

We have measured photoluminescence of ZnSxTe1-x alloys (x > 0.7) at 300 K and under hydrostatic pressure up to 7 GPa. The spectra contain only a broad emission band under excitation of the 406.7 nm line. Its pressure coefficients are 47, 62 and 45 meV/GPa for x = 0.98, 0.92 and 0.79 samples, which are about 26%, 7% and 38% smaller than that of the band gap in the corresponding alloys. The Stokes shifts between emission and absorption of the bands were calculated by fitting the pressure dependence of the emission intensity, being 0.29, 0.48 and 0.13 eV for the three samples, respectively. The small pressure coefficient and large Stokes shift indicate that the emission band observed in our samples may correspond to the Te isoelectronic center in the ZnSxTe1-x alloy.

Structural and PL properties of Cu-doped ZnO films

Cu-doped ZnO films with hexagonal wurtzite structure were deposited on silicon (1 1 1) substrates by radio frequency (RF) sputtering technique. An ultraviolet (UV) peak at similar to 380nm and a blue band centered at similar to 430nm were observed in the room temperature photoluminescent (PL) spectra. The UV emission peak was from the exciton transition. The blue emission band was assigned to the Zn interstitial (Zn-i) and Zn vacancy (V-Zn) level transition. A strong blue peak (similar to 435 nm) was observed in the PL spectra when the alpha(Cu) (the area ratio of Cu-chips to the Zn target) was 1.5% at 100 W, and ZnO films had c-axis preferred orientation and smaller lattice mismatch. The influence of alpha(Cu) and the sputtering power on the blue band was investigated.

Enhanced photoluminescence of Ar+ implanted sapphire before and after annealing

In this paper, we studied the changes in the photoluminescence spectra of the Ar+ ion implanted monocrystalline sapphire annealed at different atmospheres and different temperatures. Single crystals of sapphire (Al2O3) with the (1 0 (1) over bar 0) (m-samples) orientation were implanted at 623 K with 110 keV Ar+ ions to a fluence of 9.5 x 10(16) ions/cm(2). Photoluminescence measurement of the as-implanted sample shows a new emission band at 506 nm, which is attributed to the production of interstitial Al atoms. The intensity of emission band at 506 nm first increased then decreased with increase in annealing temperature. For the same annealing temperature, the intensity of PL peak at 506 nm of the sample annealed in air was higher than the sample annealed in vacuum. The experimental results show that the intensity of the PL peak at 506 nm of Ar-implanted sapphire can be enhanced by subsequent annealing with an enhancement of nearly 20 times. The influence of thermal annealing of the Ar-implanted samples on the new 506 nm emission band was discussed. (C) 2009 Elsevier B.V. All rights reserved.

Energy transfer from Tb3+ to Mn2+ in LaMgAl11O19:Tb, Mn phosphors

Luminescent properties of LaMgAl11O19:Tb, Mn phosphors were investigated. It was observed that the energy distributions of the Tb3+-emission bands associated with transitions from the D-5(3) and D-5(4) levels to F-7(J) depend on the Tb3+-concentration, which is due to the cross-relaxation between Tb 31 ions. The emission band at about 516 nm is attributed to the T-4(1) -> (6)A(1) transition of the Mn2+ ions. We observed an energy transfer from the Tb 3, to Mn2+ ions in LaMgAl11O19:Tb, Mn.

One-dimensional CaWO4 and CaWO4:Tb3+ nanowires and nanotubes: electrospinning preparation and luminescent properties

One-dimensional CaWO4 and CaWO4:Tb3+ nanowires and nanotubes have been prepared by a combination method of sol-gel process and electrospinning. X-Ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), photoluminescence (PL), low voltage cathodoluminescence (CL) and time-resolved emission spectra, as well as kinetic decays were used to characterize the resulting samples. The results of XRD, FT-IR, TG-DTA indicate that the CaWO4 and CaWO4: Tb3+ samples begin to crystallize at 500 degrees C with the scheelite structure. Under ultraviolet excitation and low-voltage electron beams excitation, the CaWO4 samples exhibit a blue emission band with a maximum at 416 nm originating from the WO42- groups, while the CaWO4:Tb3+ samples show the characteristic emission of Tb3+ corresponding to (D4-F6,5,4,3)-D-5-F-7 transitions due to an efficient energy transfer from WO42- to Tb3+.

Fabrication and Luminescence Properties of One-Dimensional CaMoO4: Ln(3+) (Ln = Eu, Tb, Dy) Nanofibers via Electrospinning Process

One-dimensional CaMoo(4):Ln(3+) (Ln = Eu, Tb, Dy) nanofibers have been prepared by a combination method of sol-gel and electrospinning process. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), photoluminescence (PL), and low voltage cathodoluminescence (CL) as well as kinetic decays were used to characterize the resulting samples. SEM and TEM analyses indicate that the obtained precursor fibers have a uniform size, and the as-formed CaMoO4:Ln(3+) nanofibers consist of nanoparticles. Under ultraviolet excitation, the CaMoO4 samples exhibit a blue-green emission band with a maximum at 500 nm originating from the MoO42- groups. Due to an efficient energy transfer from molybdate groups to dopants, CaMoO4:Ln(3+) phosphors show their strong characteristic emission under ultraviolet excitation and low-voltage electron beam excitation.

Solvothermal synthesis of well-dispersed NaMgF3 nanocrystals and their optical properties

Complex metal fluoride NaMgF3 nanocrystals were successfully synthesized via a solvothermal method at a relatively low temperature with the presence of oleic acid, and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectra, photoluminescence (PL) excitation and emission spectra, respectively. fit the synthetic process, oleic acid as a Surfactant played a Crucial role in confining the growth and solubility of the NaMgF3 nanocrystals. The as-prepared NaMgF3 nanocrystals have quasi-spherical shape with a narrow distribution. A possible formation mechanism of the nanocrystals was proposed based on the effect of oleic acid. The as-prepared NaMgF3 nanocrystals are highly crystalline and well-dispersed in cyclohexane to form stable and clear colloidal Solutions, which demonstrate a strong emission band centered at 400 nm in photoluminescence (PL) spectra compared with the cyclohexane solvent.

Preparation and luminescence properties of Mn2+-doped ZnGa2O4 nanofibers via electrospinning process

One-dimensional Mn2+-doped ZnGa2O4 nanofibers were prepared by a simple and cost-effective electrospinning process. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric and differential thermal analysis (TG-DTA), scanning electron microscopy (SEM), energy-dispersive X-ray spectrum (EDS), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), photoluminescence (PL) and cathodoluminescence (CL) spectra as well as kinetic decays were used to characterize the samples. SEM results indicated that the as-formed precursor fibers and those annealed at 700 degrees C are uniform with length of several tens to hundred micrometers, and the diameters of the fibers decrease greatly after being heated at 700 degrees C. Under ultraviolet excitation (246 nm) and low-voltage electron beams (1-3 kV) excitation, the ZnGa2O4:Mn2+ nanofibers presents the blue emission band of the ZnGa2O4 host lattice and the strong green emission with a peak at 505 nm corresponding to the T-4(1)-(6)A(1) transition of Mn2+ ion.

Remarkable changes in the optical properties of CeO2 nanocrystals induced by lanthanide ions doping

Highly uniform and well-dispersed CeO2 and CeO2:Eu3+ (Sm3+, Tb3+) nanocrystals were prepared by a nonhydrolytic solution route and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS), UV/vis absorption, and photoluminescence (PL) spectra, respectively. The result of XRD indicates that the CeO2 nanocrystals are well crystallized with a cubic structure. The TEM images illustrate that the average size of CeO2 nanocrystals is about 3.5 nm in diameter. The absorption spectrum of CeO2:Eu3+ nanocrystals exhibits red-shifting with respect to that of the undoped CeO2 nanocrystals. Under the excitation of 440 nm (or 426 nm) light, the colloidal solution of the undoped CeO2 nanocrystals shows a very weak emission band with a maximum at 501 nm, which is remarkably enhanced by doping additional lanthanide ions (Eu3+, Tb3+, Sm3+) in the CeO2 nanocrystals. The emission band is not due to the characteristic emission of the lanthanide ions but might arise from the oxygen vacancy which is introduced in the fluorite lattice of the CeO2 nanocrystals to compensate the effective negative charge associated with the trivalent ions.

Nanostructured CaWO4, CaWO4 : Pb2+ and CaWO4 : Tb3+ particles: Polyol-mediated synthesis and luminescent properties

Nano-submicrostructured CaWO4, CaWO4 : Pb2+ and CaWO4 : Tb3+ particles were prepared by polyol method and characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Fourier transform infrared spectra (FT-IR), thermogravimetry-differential thermal analysis (TG-DTA), photoluminescence (PL), cathodo-luminescence (CL) spectra and PL lifetimes. The results of XRD indicate that the as-prepared samples are well crystallized with the scheelite structure of CaWO4. The FE-SEM images illustrate that CaWO4 and CaWO4 : Pb2+ and CaWO4 : Tb3+ powders are composed of spherical particles with sizes around 260, 290, and 190 nm respectively, which are the aggregates of smaller nanoparticles around 10-20 nm. Under the UV light or electron beam excitation, the CaWO4 powders exhibits a blue emission band with a maximum at about 440 nm. When the CaWO4 particles are doped with Pb2+, the intensity of luminescence is enhanced to some extent and the luminescence band maximum is red shifted to 460 nm. Tb3+-doped CaWO4 particles show the characteristic emission of Tb3+ D-5(4)-F-7(J) (J=6-3) transitions due to an energy transfer from WO42- groups to Tb3+.

Synthesis, structure, photoluminescence, and electroluminescence properties of a new dysprosium complex

A new dysprosium complex Dy(PM)(3)(TP)(2) [where PM = 1-phenyl-3-methyl-4-isobutyryl-5-pyrazolone and TP = triphenyl phosphine oxide] was synthesized, and its single-crystal structure was also studied. Its photophysical properties were studied by absorption spectra, emission spectra, fluorescence quantum efficiency, and decay time of the f-f transition of the Dy3+ ion. In addition, the antenna effect was introduced to discuss the energy transfer mechanism between the ligand and the central Dy3+ ion. Finally, a series of devices with various structures was fabricated to investigate the electroluminescence (EL) performances of Dy(PM)(3)(TP)(2). The best device with the structure ITO/CuPc 15 nm/Dy complex 70 nm/BCP 20 nm/AlQ 30 nm/LiF 1 nm/Al 100 nm exhibits a maximum brightness of 524 cd/m(2), a current efficiency of 0.73 cd/A, and a power efficiency of 0.16 lm/W, which means that a great improvement in the performances of the device was obtained as compared to the results reported in published literature. Being identical to the PL spectrum, the EL spectrum of the complex also shows characteristic emissions of the Dy3+ ion, which consist of a yellow band at 572 nm and a blue emission band at 480 nm corresponding to the F-4(9/2)-H-6(13/2) and F-4(9/2)-H-6(15/2) transition of the Dy3+ ion, respectively. Consequently, an appropriate tuning of the blue/yellow intensity ratio can be presumed to accomplish a white luminescent emission.

Luminescent properties of RE3+-activated CaAl2B2O7 (RE = Tb, Ce) in VUV-visible region

RE3+-activated alpha- and beta-CaAl2B2O7 (RE = Tb, Ce) were synthesized with the method of high-temperature solid-state reaction. Their VUV excitation and VUV-excited emission spectra are measured and discussed in the present article. The charge transfer band of Tb3+ and Ce3+ is respectively calculated to be at 151 +/- 2 and 159 +/- 3 nm. All the samples show an activator-independent excitation peak at about 175 nm and an emission peak at 350-360 nm ascribed to the host absorption and emission band, respectively.

Assembly of one-dimensional organic luminescent nanowires based on quinacridone derivatives

The quinacridone derivatives N,N'-dialkyl-1,3,8,10-tetramethylquinacridone (CnTMQA, n = 6, 10, 14) were used as building blocks to assemble luminescent nano- and microscale wires. It was demonstrated that CnTMQA with different lengths of alkyl chains display obviously different wire formation properties. C10TMQA and C14TMQA showed a stronger tendency to form 1-D nano- and microstructures compared with C6TMQA. The C10TMQA molecules could be employed to fabricate the wires with different diameters, which exhibited a size-dependent luminescence property. The emission spectrum of the C10TMQA wires with diameters of 200-500 nm shows a broad emission band at 560 nm and a shoulder at around 535 nm, while the emission spectrum of the C10TMQA wires with diameters of 2-3 mu m reveals a narrower emission band at 563 nm. For the CnTMQA-based samples with different morphologies, the emission property change tendency agrees with that of the powder X-ray diffraction patterns of these samples.

Luminescence properties of CdSiO3 : Mn2+ phosphor

A novel long-lasting phosphor CdSiO3:Mn2+ is reported in this paper. The Mn2+-doped CdSiO3 phosphor emits orange light with CIE chromaticity coordinates x = 0.5814 and y = 0.4139 under 254 nm UV light excitation. In the emission spectrum of 1% Mn2+-doped CdSiO3 phosphor, there is a broad emission band centered at 575 nm which can be attributed to the,pin-forbidden transition of the d-orbital electron associated with the Mn2+ ion. The phosphorescence can be seen by the naked eyes in the dark clearly even after the 254 nm UV irradiation have been removed for about 1 h. The mechanism of the origin of the long-lasting phosphorescence was discussed using the thermoluminescence curves.

Tunable photoluminescent and cathodoluminescent properties of ZnO and ZnO : Zn phosphors

ZnO and ZnO: Zn powder phosphors were prepared by the polyol-method followed by annealing in air and reducing gas, respectively. The samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), X-ray photoelectron spectra (XPS), electron paramagnetic resonance (EPR), and photoluminescence (PL) and cathodoluminescence ( CL) spectra, respectively. The results indicate that all samples are in agreement with the hexagonal structure of the ZnO phase and the particle sizes are in the range of 1-2 mu m. The PL and CL spectra of ZnO powders annealed at 950 degrees C in air consist of a weak ultraviolet emission band ( similar to 390 nm) and a broad emission band centered at about 527 nm, exhibiting yellow emission color to the naked eyes. When the sample was reduced at the temperatures from 500 to 1050 degrees C, the yellow emission decreased gradually and disappeared completely at 800 degrees C, whereas the ultraviolet emission band became the strongest. Above this temperature, the green emission ( similar to 500 nm) appeared and increased with increasing of reducing temperatures.