Papers by Keyword: Photoluminescence (PL)

Abstract: Lanthanum calcium phosphate glasses doped with Eu³⁺ ions in compositions 20La₂O₃:10CaO:(70-x)P₂O₅:xEu₂O₃ (where x = 0.05, 0.10, 0.50 and 1.50 mol%) were prepared by melt-quenching technique. The density and molar volume measurements were carried out at room temperature. The absorption spectra were investigated in the UV-Vis-NIR region from 200 to 2500 nm. The emission spectra of Eu³⁺-doped glasses centered at 590 nm (⁵D₀→⁷F₁), 612 nm (⁵D₀→⁷F₂), 652 nm (⁵D₀→⁷F₃) and 699 nm (⁵D₀→⁷F₄) have been observed with 393 nm excitation wavelength.

Abstract: We study the GaSb/GaAs nanostructures (NSs) grown by droplet epitaxy technique with various Ga amounts. Ga amount deposited on the GaAs (001) substrate was varied between 3-5 ML to form the different size and density of liquid Ga droplets. The Sb flux was subsequently irradiated to crystallize the droplets. Morphology of GaSb NSs was investigated by atomic force microscopy (AFM). Quantum rings were obtained after crystallizing 3-ML Ga droplets, whereas some kind of quantum dots were formed after crystallizing 4-and 5-ML Ga droplets. The formation mechanisms leading to the different structure are discussed. The photoluminescence (PL) measurement was performed to examine the optical properties of GaSb/GaAs NSs.

Abstract: A novel blue-emitting phosphor NaBaBO₃ doped with Tm³⁺ was prepared using a conventional high temperature solid-state reaction method. Its crystal structure and luminescence properties were studied. Photoluminescence measurements indicate that the phosphor features a satisfactory blue performance due to the ¹D₂→³F₄ transition of Tm³⁺ with the highest photoluminescence intensity located at 460 nm excited by 359 nm near-ultraviolet (NUV) light. In addition, the concentration of Tm³⁺ was adjusted in order to obtain the optimum emission intensity. When the Tm³⁺ concentration in NaBaBO₃ is 6.0 mol% the maximum intensity can be obtained. The concentration quenching occurs when Tm³⁺ concentration is beyond 6.0 mol% and the concentration quenching mechanism can be explained by the dipole–dipole interaction. The measured chromaticity coordinate for the NaBaBO₃:Tm³⁺phosphor under 359 nm excitation is determined to be (0.1470, 0.1090). The present work suggests that the NaBaBO₃:Tm³⁺,K⁺ phosphor is a promising blue-emitting material for NUV white light-emitting diodes.

Abstract: Finely-dispersed phosphors of Y₂O₃:Eu and Y₃Al₅O₁₂:Eu have been synthesized with the help of Pechini method and the method of self-propagating high-temperature synthesis (SHS). During the synthesis of phosphors on the basis of Y₂O₃ carried out with Pechini method the size of crystallites increases with the enlargement of concentration of yttrium, but it decreases when the method of SHS is applied. The structure of phosphors on the basis of Y₃Al₅O₁₂ (YAG) is strongly amorphized. This fact agrees with the data of XRD and with the prevalence of the band with λ_max = 613 nm in the spectra of this phosphor. The enlargement of yttrium concentration in it promotes the amorphisation of yttrium aluminum garnet and the decrease of a crystal phase content. The sample of Y₃Al₅O₁₂:Eu synthesized with Pechini method has the maximum intensity, while in conditions of excitement with “high-level” X-ray radiation which corresponds to the radiation of industrial medical X-ray apparatus, the phosphor of Y₂O₃:Eu synthesized with the help of SHS showed the largest intensity. Colloid solutions prepared with the use of the samples synthesized by SHS method revealed a higher steadiness and a lower disposition to the sedimentation process. The samples of Y₂O₃:Eu phosphor possessing the smallest size of particles and the highest intensity of X-ray luminescence are the most suitable for the creation of pharmacological drugs used for photodynamic therapy.

Abstract: CdSiO₃: Ce³⁺ (1-11mol %) nanophosphors were prepared by low temperature solution combustion method using Oxalyl di-hydrazine (ODH) as fuel. The final products were well characterized by PXRD and SEM. The optical properties of the nanophosphors were investigated by Photoluminescence studies. PXRD results evident that CdSiO₃ phosphor shows pure single monoclinic structure. The average crystallite size was calculated using Debye – Scherer’s formula and was found to be in the range of 30-40 nm. The SEM micrographs show phosphors with high porosity and irregular shaped particles. Photoluminescence peaks observed at 454, 563 and 679 nm under 397 nm excitation was due to transition from 5d state to the ²F_5/2 and ²F_7/2 components of the ground state of Ce³⁺ in CdSiO₃ host material. CdSiO₃:Ce³⁺ nanophosphors show an intense yellow emission with CIE coordinates (0.47, 0.50) with average correlated color temperature value 3284 was within the range of vertical day light. The present study successfully demonstrates solution combustion synthesis of nanophosphors for display applications.

Abstract: Porous silicon (p-Si) was fabricated by single-groove electrochemical anodic etching method; the influence of large etching current density on the surface morphology was observed. And the surface microstructure and photoluminescence (PL) of p-Si were shown by scanning electron microscope (SEM) and PL spectra, respectively. The SEM image showed that a new microstructure was formed at the large current density etching area, which resembled a crater structure; and the area away from the crater appeared the porous structure. The comparison results of the PL spectra for the different areas indicated that PL of the crater area has a shorter wavelength.

Abstract: A strong, simple and rapid method for determination enzyme (papain) conjugated quantum dots (QDs) by dynamic light scattering (DLS) is proposed in this report. Yellow CdSe QDs are synthesized with changing the precursor ratio and confirmed by absorption and emission spectra. Shape and size of synthesized QDs are checked by transmission electron microscope (TEM). Both absorption and emission spectra reveal very strong quantum confinement effect as expected; yellow excitonic emission is observed at room temperature for photoluminescence spectra (PL). The peak maxima are appreciably red-shifted when QDs are conjugated with positively charged papain enzyme. The details possible mechanism is described here, which is very interesting and scarcely addressed before.

Abstract: In the hydrothermal system, In (OH)₃ nanobelts were obtained. After heat-treatment at 300 °C, In₂O₃ single crystals nanobelts were produced, which can keep the morphologies and sizes of precursors. The room temperature PL spectra of as-prepared In₂O₃ nanobelts are also detected. PL peaks of In₂O₃ nanobelts mainly focused at 458 nm (blue).

Abstract: The optical and chemical properties of gallium arsenide (GaAs) surfaces treated by ammonium sulfide ((NH₄)₂S) treatments were studied via low-temperature photoluminescence (PL). From the PL mapping and Atomic Force Microscope (AFM) results, the treatment process by (NH₄)₂S is quite effective to remove the oxide layer of GaAs.The PL intensity of (NH₄)₂S-passivated sample was higher than the untreated sample, and the homogeneity of passivated surface was much better. This strategy provides superior promising passivation method for III-V compound semiconductor material in high-speed and optoelectronic device applications.

Abstract: SnO₂ nanocrystalline thin films (NCTFs) with high quality and low infrared emissivity were synthesized through a simple hydrothermal process designed by orthogonal design theory. The microstructure, morphology, photoluminescence (PL) property and the infrared emissivity (IRE) property of as-prepared products were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), fluorescence spectrophotometer, and infrared spectroradio meter (ISM) respectively. The results show that two emission peaks are observed in PL spectra, which can be deconvoluted by Gaussian profile fitting into four emission peaks centered at about 380, 420, 460 and 520 nm respectively. The influences of crystallinity, concentration of particles and resistivity on IRE were systematically investigated, revealing that the better crystallinity, higher particle density and better conductivity are favorable for lowering IRE.