K. Kurt

Influence of phase transitions of ice on near-surface cathodoluminescence

Luminescence signals respond to phase transitions both of the host material and of impurities on the nanoparticle-size scale. During cathodoluminescence spectral measurements of many insulators, strong intensity changes (up to 100 times) have been recorded at ~170 K, which are here ascribed to the phase transitions of water that has diffused into the near-surface regions, or is trapped within the bulk material in nanoparticle quantities. The intensity step correlates with the ice transition between the cubic and hexagonal phases. In many materials there are also weaker features near 230 K which match the low-pressure ice-to-vapour transition. Some signals are apparent in radioluminescence data when the water is within the bulk material. The impurity phase changes can modify the emission spectra of the host. Examples are given for several insulators (Nd:YAG, zircon, MgO:Cr, PbWO4, strontium barium niobate) and a superconductor. The data have implications for quantitative luminescence analyses and underline the significant and influential presence of water contaminants. In many surface layers, such as surface optical waveguides or those of superconductors, the ice may significantly influence the behaviour of the host material.

Luminescence characterisation of defects in pld alumina and copper implanted silica

Abstract Luminescence is reported for alumina and Al 2 O 3 :Cu films grown by pulsed laser deposition and is contrasted with luminescence from Cu ion implanted silica. The implanted samples display numerous emission bands with at least two associated to charge states or the Cu ions. The relative band intensities are altered by thermal treatments. In the case of the thin films the signals are sensitive to the growth conditions and show evidence for trapped Ar nanoparticles, from argon used as a background gas during film growth. Thus in both thin film and ion implanted material the luminescence offers a route to monitor the state of the defects and the copper impurity ions.

A novel and simple expression to accurately calculate the resonant frequency of annular-ring microstrip antennas

This paper proposes a novel and simple expression for effective radius of annular-ring microstrip antennas (ARMAs) obtained using a recently emerged optimization algorithm of artificial bee colony (ABC) in calculating the resonant frequency at dominant mode (TM 11 ). A total of 80 ARMAs having different parameters related to antenna dimensions and dielectric constants was simulated in terms of the resonant frequency with the help of an electromagnetic simulation software called IE3D™ based on method of moment. The effective radius expression was constructed and the unknown coefficients belonging to the expression were then optimally determined with the use of ABC algorithm. The proposed expression was verified through comparisons with the methods of resonant frequency calculation reported elsewhere. Also, it was further validated on an ARMA fabricated in this study. The superiority of the presented approach over the other methods proposed in the literature is that it does not need any sophisticated computations while achieving the most accurate results in the resonant frequency calculation of ARMAs.

Detection of phase transitions in RbTiOPO4 and KTiOPO4 by luminescence

Luminescence signals have been recorded at low temperature during thermal cycling of crystals of RbTiOPO4 (RTP) and KTiOPO4 (KTP) excited by x-rays. In both crystals there are well resolved intense intensity spikes and changes in emission spectra consistent with first-order phase transitions. The transitions are not reversible, except by high temperature annealing. The observations imply that new phases of RTP and KTP can be formed, and in some cases these may relate to nanoparticle-size inclusions. Crystal quality assessment from the luminescence behaviour may have value for non-linear optics. Cathodoluminescence of the RTP surface reveals different emission spectra from the bulk material with consequent implications for usage in surface waveguide devices.

ANFIS model for determining resonant frequency of rectangular ring compact microstrip antennas

In this work, a model constructed with the adaptive neuro - fuzzy inference system (ANFIS) for estimating the resonant frequency of rectangular ring compact microstrip antennas (RRCMAs) in UHF band is proposed. A total of 108 RRCMAs having different parameters related to the antenna dimensions and dielectric substrate were simulated with the help of electromagnetic packaged software IE3D TM based on method of moment (MoM) to generate the data pool for training and test processes of the ANFIS model. While 96 RRCMAs were employed for training, the remainders were used for test the ANFIS model. The resonant frequencies were computed with the average percentage errors (APE) as 0.014% and 0.666% for training and test, respectively. The accuracy of proposed model was successfully demonstrated by comparing with the results of a method over the simulated data previously published in the literature. Further to inspect the validity of the ANFIS model, a RRCMA operating at 2.44 GHz was designed and fabricated for this work, and the accurate results concerning the resonant frequency were achieved.