Papers by Gerard O'Connor
Near-infrared (785 nm) excitation was used to obtain Raman spectra from a series of 33 solid mixt... more Near-infrared (785 nm) excitation was used to obtain Raman spectra from a series of 33 solid mixtures containing cocaine, caffeine and glucose (9.8-80.6% by weight cocaine), which were then analysed using chemometric methods. Principal component analysis of the data was employed to ascertain what factors influenced the spectral variation across the concentration range. It was found that 98% of the spectral variation was accounted for by three principal components. Analysis of the score and loadings plots for these components showed that the samples can be clearly classified on the basis of cocaine concentration. Discrimination on the basis of caffeine and glucose concentrations was also possible. Quantitative calibration models were generated using partial least-squares algorithms which predicted the concentration of cocaine in the solid mixtures containing caffeine and glucose from the Raman spectrum with a root mean standard error of prediction (RMSEP) of 4.1%. Caffeine and glucose concentrations were estimated with RMSEPs of 5.2 and 6.6%, respectively. These measurements demonstrate the feasibility of using near-IR Raman spectroscopy for rapid quantitative characterization of illegal narcotics.
IEEE Journal of Quantum Electronics, 1997
A comparative luminescence study of two Ga 0:52 In 0:48 P-(Al 0:5 Ga 0:5 ) 0:52 In 0:48 P single-... more A comparative luminescence study of two Ga 0:52 In 0:48 P-(Al 0:5 Ga 0:5 ) 0:52 In 0:48 P single-quantum-well (SQW) samples with bulk and multiquantum barrier (MQB) barriers is presented. When excess carriers are only created in the quantum wells (QW's) of the samples by resonant excitation using a dye laser, the luminescence efficiency of both samples as a function of temperature is found to be essentially identical. We find, therefore, no evidence for any enhancement in the confining potential of the MQB sample over the bulk barrier sample. From Arrhenius plots of the integrated luminescence intensity, it is found that carrier loss from the QW is dominated by a nonradiative loss mechanism with an activation energy considerably smaller than that expected from direct thermal loss of electrons and holes into the barriers. We suggest that the improved device characteristics reported for lasers containing MQB's is due to effects other than the quantum interference of electrons.
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Papers by Gerard O'Connor