Papers by Keyword: Photoluminescence (PL)

Abstract: We report the structural and optical properties of a-Al2O3 film grown on porous silicon substrate using sol-gel method. The results indicated that a-Al2O3 film were grown after it sintering at 1200 °C for 1 hour and the scanning electron microscopy image shows the a-Al2O3 film has a nanostructure. From the photoluminescence spectrum, it shows that a narrow purple emission peak. This proved porous silicon is a good substrate to grow a-Al2O3 film.

Abstract: PbWO4 crystals were synthesized by homogeneous precipitation in formamide (FA)/H2O solution, where the content of FA was found to play crucial role in the morphology of the final products. PbWO4 crystals with various morphologies, such as pagoda, tetra-bipyramid, and bundle of rods, were obtained with an increase of the content of FA. The products were characterized by XRD and photoluminescence measurements.

Abstract: Powders of tin dioxide (SnO2) have been prepared by two different modifications of wet chemical synthesis, i.e. (i) by conventional hydrolysis of tin chloride dissolved in aqueous ammonia solution and (ii) by precipitation from tin chloride dissolved in aqueous hydrazine monohydrate (N2H4*H2O) solution. The prepared gels were dried and then annealed at different temperatures varied from 300 to 700 oC in order to form nanocrystals. Structure and optical properties of the samples were investigated by using X-ray diffraction, transmission electron microscopy, thermoprogrammable hydrogen reduction, low temperature nitrogen adsorption method, photoluminescence, infra-red absorption, Raman spectroscopy, and X-ray photoelectron spectroscopy. The samples prepared by hydrazine-based method are characterized by surface area about 127-188 m2/g with high sintering resistance. The optical spectroscopy data revealed pure crystallinity and high defect concentration for the samples prepared by hydrazine-based method. The experimental results are discussed in view of different states of chemisorbed oxygen on SnO2 nanocrystal surfaces, which determine electronic and optical properties of the prepared samples.

Abstract: In the current study long afterglow phosphors in strontium aluminate system doped with Eu2+ and Dy3+ were synthesized at different firing temperatures for various time. Photoluminescency and crystallisation during sintering under reducing atmosphere were examined as functions of sintering time and temparature. XRD was employed to characterize the crystal phases of phosphors. Scanning electron microscopy (SEM) investigations were carried out to understand surface morphology and to confirm the XRD results. The optical properties of the phosphors were investigated by a phosphorescence spectrophotometer. The changes in emission and excitation spectrum were discussed accounting firing time and temperature.

Abstract: The detailed preparation process of Eu2+ and Dy3+ ion co-doped phosphor powders in Sr4Al14O25:Eu2+/Dy3+ phosphor system with bluish-green long afterglow produced by solid state reaction method under reducing atmosphere is here reported. X-ray diffraction (XRD), scanning electron microscopy (SEM), and particle size analysis were made to assign the effects of Eu and Dy ions on the luminescent properties of the synthesized phosphors, which were determined by measuring the photoluminescence spectra. The maximum emission intensity of these phosphors under excitation was investigated. As a result, the relevant values were obtained from the phosphorescent pigment with 0.21% and 0.05% molar percent of Eu2+ and Dy3+.

Abstract: We examined photoluminescent (PL) and afterglow properties in bazirite (BaZrSi3O9) phases with Sr2+-, Sn4+-, Ge4+-, and Ti4+-impurities, in order to elucidate effect of the impurity-addition on these properties. The bazirite phases studied showed blue PL and afterglow regardless of sort of the impurities. Origin of PL and afterglow emission in the bazirite phase is also discussed.

Abstract: Shrinking the size of a solid down to nanometer scale is indeed fascinating, which makes all the otherwise constant physical quantities to be tunable such as the Young’s modulus, dielectric constant, melting point, etc. The variation of size also generates novel properties that can hardly be seen in the bulk such as the conductor-insulator and nonmagnetic-magnetic transition of noble metals at the nanoscale. Although the physics of materials at the nanoscale has been extensively investigated, the laws governing the energetic and dynamic behavior of electrons at such a scale and their consequences on the tunable physical properties of nanostructures have not been well understood [C. Q. Sun, Prog Solid State Chem 35, 1-159 (2007); Prog Mater Sci 54, 179-307 (2009)]. The objective of the contribution is to update the recent progress in dealing with the coordination-resolved energetic and dynamic behavior of bonds in the low-dimensional systems with consideration of the joint effect of temperature and pressure. It is shown that the broken-bond-induced local strain and the associated charge and energy quantum trapping at the defect sites perturbs the atomic cohesive energy, electroaffinity, the Hamiltonian and the associated properties of entities ranging from point defects, surfaces, nanocavities and nanostructures. Application of the theories to observations has led to consistent understanding of the behavior of nanometer-sized materials and the interdependence of these entities as well as the means of determining the bond energy through the temperature-dependent measurements.

Abstract: Single crystal silicon (sc-Si) wafers are widely used as the precursors to prepare silicon nanowires (SiNWs) by employing a silver-assisted chemical etching process. In this work, we obtained SiNWs arrays using multicrystalline silicon (mc-Si) wafers. Firstly, silver nanoparticles were deposited on the textured solar-grade mc-Si wafer by a galvanic displacement process; secondly, the SiNWs arrays were formed by a silver-assisted chemical etching process conducted in a HF-H2O2 aqueous solution. The etching process indicated that the growth of SiNWs is independent on the orientation of the Si wafer. TEM images showed that the SiNWs have rough and nanoporous structures on the top side along axial directions. The photoluminescence (PL) spectrum of SiNWs showed a broad visible emission centred around 700 nm, which is attributed to the emission properties of silicon nanocrystallites in SiNWs. This work may contribute to the development of SiNWs in application including optoelectronic devices, solar energy conversion devices, chemical sensors, and lithium secondary batteries, etc.

Abstract: Magnetoplumbite-type (M-type) strontium ferrite particles with two stoichiometric ratios (SrFexO19; x = 9.2 and 11.6) have been synthesized via the sol-gel technique employing ethylene glycol as the gel precursor. The prepared samples were characterized using x-ray diffractometry (XRD), thermogravimetric analysis (TGA), photoluminescence (PL) spectrophotometry, field emission scanning electron microscopy (FESEM), energy dispersive x-ray spectrometry (EDS) and superconductivity quantum interference device magnetometry (SQUID). X-ray powder diffraction patterns showed that the samples were single-phase with the space group of P63/mmc and cell parameter values of a = 5.88 Ǻ and c = 23.03 – 23.04 Ǻ. EDS results confirmed the composition being mainly of M-type SrFe12O19. The photoluminescence property of strontium ferrite was examined at excitation wavelength of 260 - 290 nm and significant PL emission peaks centered at 334 nm were detected. Both as-prepared strontium ferrites exhibited significant oxygen vacancies which were detectable via TGA where the sample with the Sr/Fe ratio of 1:11.6 exhibited the highest oxygen vacancies in its structure.

Abstract: Bulk silicon is the material for microelectronics fabrication such as memory device. However, its optical properties are poor due to its indirect band gap. Since the photoluminescence from porous silicon at room temperature was first reported by Canham, silicon nanostructures have attracted considerable interest due to their potential applications in optoelectronic devices such as Si-based LEDs, solar cell. In the present study, the nanocrystalline silicons were synthesized by non-thermal plasma from gas phase. And Nitrogen plasma was applied to reduce the nonraidative recombination center which related to the emission efficiency. To confirm the effect of nitrogen plasma, the compositional, electrical and optical analysis of silicon nanocryatals layer were also investigated.