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Excitation Laser (excitation + laser)
Selected AbstractsLaser-induced phase changes in olivine FePO4: a warning on characterizing LiFePO4 -based cathodes with Raman spectroscopyJOURNAL OF RAMAN SPECTROSCOPY, Issue 2 2009Christopher M. Burba Abstract Raman spectroscopy is an excellent technique for probing lithium intercalation reactions of many diverse lithium ion battery electrode materials. The technique is especially useful for probing LiFePO4 -based cathodes because the intramolecular vibrational modes of the PO43, anions yield intense bands in the Raman spectrum, which are sensitive to the presence of Li+ ions. However, the high power lasers typically used in Raman spectroscopy can induce phase transitions in solid-state materials. These phase transitions may appear as changes in the spectroscopic data and could lead to erroneous conclusions concerning the delithiation mechanism of LiFePO4. Therefore, we examine the effect of exposing olivine FePO4 to a range of power settings of a 532-nm laser. Laser power settings higher than 1.3 W/mm2 are sufficient to destroy the FePO4 crystal structure and result in the formation of disordered FePO4. After the laser is turned off, the amorphous FePO4 compound crystallizes in the electrochemically inactive ,-FePO4 phase. The present experimental results strongly suggest that the power setting of the excitation laser should be carefully controlled when using Raman spectroscopy to characterize fundamental lithium ion intercalation processes of olivine materials. In addition, Raman spectra of the amorphous intermediate might provide insight into the ,-FePO4 to olivine FePO4 phase transition that is known to occur at temperatures higher than 450 °C. Copyright © 2008 John Wiley & Sons, Ltd. [source] Local Heating from Silver Nanoparticles and Its Effect on the Er3+ Upconversion in Oxyfluoride GlassesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2010Chao Liu The effect of silver (Ag) nanoparticles on the upconversion emission properties of Er3+ ions in oxyfluoride glasses was investigated, and a mechanism of the energy transfer proposed. The integrated intensity ratios between 522 and 545 nm emission bands of Er3+ ions in glasses containing Ag nanoparticles were strongly dependent on the size of the Ag nanoparticles as well as on the intensity of the 800 nm excitation laser. When the absorption of Ag nanoparticles overlapped with the 2H11/2 and 4S3/2 energy levels in Er3+ ions, a strong energy transfer occurred from Er3+: 2H11/2, 4S3/2 levels to Ag nanoparticles. This energy was then converted to a temperature rise in the vicinity of Er3+ ions, eventually leading to the large increase in the integrated intensity ratios. The estimated effective temperature was approximately 200 K higher than the experimental temperature when the excitation power was 700 mW. [source] Submicron resolution carrier lifetime analysis in silicon with Fano resonancesPHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 7 2010Paul Gundel Abstract Defect rich regions in multicrystalline silicon are investigated by Raman spectroscopy at high and low injection levels. By analyzing the Fano type asymmetry and the spectral position of the first order Raman peak crucial properties such as recombination lifetime, doping density and stress can be extracted simultaneously. Due to the small wavelength of the excitation laser the spatial resolution of these measurements is significantly below 1 µm, which gives new insight into the impact of defects on the carrier recombination lifetime. The results are evaluated by comparing them to micro-photoluminescence and synchrotron X-ray fluorescence measurements. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Analysis of optical loss on blue-violet laser diodesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2006J. K. Son Abstract We measured optical loss of laser diodes by taking the intensity decay of edge emitting photoluminescence with respect to the distance from cleaved edges of wafers to the position where an excitation laser was focused. Measurements were performed on wafers with different thickness of InGaN p-waveguide. We found that optical loss of wafers was determined by absorption of Mg doped GaN for narrow InGaN waveguide and by absorption of InGaN for thick InGaN waveguide. From experimental data and fittings, we obtained 40 cm,1 for InGaN absorption at 405 nm. Therefore, we conclude that the optical losses still remain even though the Mg-doped GaN regions are far enough from QWs and that absorption loss of InGaN layers is relatively high comparing with undoped GaN. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||