J. Castañeda-Contreras

Photovoltaic study of dye sensitized solar cells based on TiO2, ZnO:Al3+ nanoparticles

A technique to fabricate dye (rhodamine B) sensitized solar cells based on Titanium Oxide (TiO2) and Zinc Oxide (ZnO) nanoparticles are reported. The TiO2 was synthesized using the sol-gel method and the ZnO was synthesized by hydrolysis method to obtain nanoparticles of ~ 5 nm and 150 nm respectively. ZnO was doped with Al3+ in order to enhance the photovoltaic efficiency to promote the electrons mobility. The photovoltaic conversion characterization of films of TiO2, ZnO and ZnO:Al3+ nanoparticles is also reported. The generated photocurrent was measured by two methods; one of those uses a three electrode electrochemical cell and the other use an electronic array where the cells were exposed to UV lamp and the sun light. The role of the TiO2, ZnO and Al3+ doped ZnO nanoparticles is discussed to obtain a better efficiency in the generation of photocurrent (PC). The results exhibited by the electrochemical cell method, efficiencies of 0.55 (PC=187 μA/cm2) and 0.22 (PC=149 μA/cm2) for TiO2 and undoped ZnO respectively. However, when ZnO is doped with Al3+ at the higher concentration the efficiency was 0.44. While using the electronic array the results exhibited efficiencies of 0.31 (PC=45 μA/cm2) and 0.09 (PC=16 μA/cm2) for TiO2 and undoped ZnO respectively. However, when ZnO is doped with Al3+ at the higher concentration the efficiency was 0.44 and 0.48 for electrochemical cell and electronic array respectively. This shows that Al3+ enhances the photogenerated charge carriers increasing the mobility of electrons.

Luminescence from ascorbate-stabilized Er2O3 nanoparticles

The paper presents the way that colour can serve solving the problem of calibration points indexing in a camera geometrical calibration process. We propose a technique in which indexes of calibration points in a black-and-white chessboard are represented as sets of colour regions in the neighbourhood of calibration points. We provide some general rules for designing a colour calibration chessboard and provide a method of calibration image analysis. We show that this approach leads to obtaining better results than in the case of widely used methods employing information about already indexed points to compute indexes. We also report constraints concerning the technique. Nowadays we are witnessing an increasing need for camera geometrical calibration systems. They are vital for such applications as 3D modelling, 3D reconstruction, assembly control systems, etc. Wherever possible, calibration objects placed in the scene are used in a camera geometrical calibration process. This approach significantly increases accuracy of calibration results and makes the calibration data extraction process easier and universal. There are many geometrical camera calibration techniques for a known calibration scene [1]. A great number of them use as an input calibration points which are localised and indexed in the scene. In this paper we propose the technique of calibration points indexing which uses a colour chessboard. The presented technique was developed by solving problems we encountered during experiments with our earlier methods of camera calibration scene analysis [2]-[3]. In particular, the proposed technique increases the number of indexed points points in case of local lack of calibration points detection. At the beginning of the paper we present a way of designing a chessboard pattern. Then we describe a calibration point indexing method, and finally we show experimental results. A black-and-white chessboard is widely used in order to obtain sub-pixel accuracy of calibration points localisation [1]. Calibration points are defined as corners of chessboard squares. Assuming the availability of rough localisation of these points, the points can be indexed. Noting that differences in distances between neighbouring points in calibration scene images differ slightly, one of the local searching methods can be employed (e.g. [2]). Methods of this type search for a calibration point to be indexed, using a window of a certain size. The position of the window is determined by a vector representing the distance between two previously indexed points in the same row or column. However, experiments show that this approach has its disadvantages, as described below. * E-mail: A.Nowakowski@ire.pw.edu.pl Firstly, there is a danger of omitting some points during indexing in case of local lack of calibration points detection in a neighbourhood (e.g. caused by the presence of non-homogeneous light in the calibration scene). A particularly unfavourable situation is when the local lack of detection effects in the appearance of separated regions of detected calibration points. It is worth saying that such situations are likely to happen for calibration points situated near image borders. Such points are very important for the analysis of optical nonlinearities, and a lack of them can significantly influence the accuracy of distortion modelling. Secondly, such methods may give wrong results in the case of optical distortion with strong nonlinearities when getting information about the neighbouring index is not an easy task. Beside this, the methods are very sensitive to a single false localisation of a calibration point. Such a single false localisation can even result in false indexing of a big set of calibration points. To avoid the above-mentioned problems, we propose using a black-and-white chessboard which contains the coded index of a calibration point in the form of colour squares situated in the nearest neighbourhood of each point. The index of a certain calibration point is determined by colours of four nearest neighbouring squares (Fig.1). An order of squares in such foursome is important. Because the size of a colour square is determined only by the possibility of correct colour detection, the size of a colour square can be smaller than the size of a black or white square. The larger size of a black or white square is determined by the requirements of the exact localisation step which follows the indexing of calibration points [3]. In this step, edge information is extracted from a blackand-white chessboard. This edge information needs larger Artur Nowakowski, Wladyslaw Skarbek Institute of Radioelectronics, Warsaw University of Technology, Nowowiejska 15/19, 00-665 Warszawa, A.Nowakowski@ire.pw.edu.pl Received February 10, 2009; accepted March 27, 2009; published March 31, 2009 http://www.photonics.pl/PLP

Structural and photoluminescence characterization of nanocrystalline YAG: Er3+ prepared with the addition of PVA and UREA

The Photoluminescence (PL), FFTIR, Raman characterization, XRD and TEM of Er doped nanocrystals (Y3Al5O12:Er) prepared by glycolate method modified with PVA and UREA is reported. Irregular morphology was observed but for some concentration of PVA and UREA nanorods was observed, being PVA dominant in final morphology. XRD patterns show the presence of hexagonal phase of YAG (YAH) when the UREA was used but pure YAG crystalline structure was obtained with only PVA. Raman spectroscopy confirms the crystalline phase and in combination with infrared spectroscopy the presence of oxygen deficiency was observed. Strong green emission was observed as a result of the upconversion mechanism due to the two photon process. Luminescence results show that both PVA and UREA do not modify the emission properties but control the morphology.

Determination Of Nanoporosity And Free Volume In A Polymer Blend System By Means Of Positronium Spectroscopy

A polymer system is studied (a PMMA + MMA + TEGDMA blend) whose free volume properties are determinant for the process of blending and packaging of polymer chains. In this case a possible influence of the Flory-Huggins interaction parameter on the free volume fraction of the blend is discussed. An exhaustive revision of the current nanoporosity models for the characterisation of materials is also presented as well as a graphical method to determine nanometer-sized spaces, which contributes to the achievement of numerical solutions to the stationary Schrodinger equation.

Erbium up conversion in SiO2-TiO2 sol gel powders

Erbium doped, SiO2 - TiO2 powders were fabricated using the sol gel technique. The Er3+ concentrations were 2%, 5% and 10% (mol), and 10%, 25%, 50%, 70% for the TiO2. A strong, green up-conversion luminescence was found in the samples when exciting at 1532 nm and 978 nm. The recorded spectra showed less intense emissions at 410 nm and 675 nm. The excitation and emission mechanisms proposed were supported on experimental results, such as the absorption and emission spectra, the decay times and the luminescence intensity versus pump power.