Joanna Janek

Spectroscopic properties of Eu3+, Dy3+ and Tb3+ ions in lead silicate glasses obtained by the conventional high-temperature melt-quenching technique

The luminescence properties of selected rare-earth ions in lead silicate glasses have been studied. Europium, dysprosium and terbium ions were chosen as active dopants. Based on excitation and emission measurements as well as luminescence decay analysis, some spectroscopic parameters for these lanthanide ions were determined. In particular, the intensity ratios R/O (Eu3+), Y/B (Dy3+) and G/B (Tb3+) were calculated. Luminescence lifetimes for the 5D0 state of Eu3+ ions, the 4F9/2 state of Dy3+ ions and the 5D4 state of Tb3+ ions were also determined.

Polymorphs of oxindole as the core structures in bioactive compounds

A new polymorph of oxindole (termed as “δ-form”) has been found and characterized by single-crystal X-ray diffraction. Its structural properties were compared with those of the previously reported polymorphs (the α-, β- and γ-forms). This polymorphic form was crystallized for the first time but could not be reproduced. Thus, the δ-form can serve as an example of a “disappearing polymorph”. As a result, the three previously reported α-, β- and γ-forms have now been characterized by powder X-ray diffraction, vibrational spectroscopy (infrared and Raman) and calorimetry (differential scanning calorimetry). In the structures of the earlier known α- and β-forms, N–H⋯O hydrogen bonds connect the molecules into dimers, while the crystals of the γ- and δ-forms contain hydrogen-bonded chains of associated molecules. An analysis of the Hirshfeld surfaces and fingerprint plots has also been performed to study the intermolecular interactions in the crystal network of each polymorph. The spectroscopic and thermal investigations showed that the polymorphs convert into the α-form, which indicates that the α-form is the most stable at ambient temperature. Additionally, the α- and β-forms are enantiotropically-related phases, whereas the γ-form is monotropically related to the α-form. Unexpectedly, the β- and γ-forms were found to be unstable under Cu Kα radiation and both gradually transformed into the α-form with the γ-phase being more stable.

Green and red up-conversion luminescence of Er3+ in lead silicate glass under excitation of Yb3+

Lead silicate glasses co-doped with Yb3+/Er3+ have been investigated. Up-conversion luminescence spectra of Er3+ ions were registered under excitation of Yb3+ ions by 980 nm diode laser line. Green and red luminescence bands correspond to the 4S3/2 - 4I15/2 and 4F9/2 - 4I15/2 transitions of Er3+, respectively. The luminescent transitions of Er3+ ions have been also examined with temperature.

Energy transfer processes between rare earth ions and white light emission in inorganic glasses

In this paper, lead borate glasses singly, doubly and triply doped with rare earth ions were investigated using optical spectroscopy. Luminescence spectra of rare earths were detected under various excitation wavelengths. The main green luminescence band related to ⁵D₄ → ⁷F₅ transition of Tb³⁺ is observed under excitation of Dy³⁺. The main red emission band due to ⁵D₀ → ⁷F₂ transition of Eu³⁺ is well observed under direct excitation of Tb³⁺. In both cases, the energy transfer processes from Dy³⁺ to Tb³⁺ and from Tb³⁺ to Eu³⁺ in lead borate glasses occur. Lead borate glass triply doped with trivalent rare earths exhibits nearly white light emission originating from the simultaneous generation of several bands of Dy³⁺, Tb³⁺ and Eu³⁺ ions under selective UV-visible excitation.

Rare earth doped lead-free germanate glasses for modern photonics

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