Biomedical subjects

T Gregorkiewicz

Publications and source records attributed to T Gregorkiewicz.

At least 19 recordsLinked to original sources

PubMed2006

Nanosecond dynamics of the near-infrared photoluminescence of Er-doped SiO2 sensitized with Si nanocrystals.

We report on an observation of a fast 1.5 microm photoluminescence band from Er3+ ions embedded in an SiO2 matrix doped with Si nanocrystals, which appears and decays within the first microsecond after the laser excitation pulse. We argue that the fast excitation and quenching are facilitated by Auger processes related to transitions of confined electrons or holes between the space-quantized levels of Si nanocrystals dispersed in SiO2. We show that a great part--about 50%--of all Er dopants is involved in these fast processes and contributes to the submicrosecond emission.

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PubMed2006

Isotope dependence of the lifetime of the vibration of oxygen in silicon.

By simply changing the isotopes of the Si atoms that neighbor an oxygen Oi atom in crystalline silicon, the measured decay rate tau of the asymmetric-stretch vibration (nu3=1136 cm-1) of oxygen (Oi) in silicon changes by a factor of approximately 2.5. These data establish that nu3 decays by creating one nu1 symmetric-stretch, local-vibrational mode of the Si-Oi-Si structure. If the residual energy (nu3-nu1) is less than the maximum frequency num of the host lattice, as for 28Si-16O-28Si in natural silicon, then it is emitted as one lattice mode, and tau depends on the density of one-phonon states at nu3-nu1. If (nu3-nu1)>num, as for 16O in single-isotope 30Si silicon, two lattice modes are created in addition to nu1, increasing tau. Prediction of tau for a particular defect clearly requires a detailed knowledge of that defect.

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PubMed2003

Microscopic structure of Er-related optically active centers in crystalline silicon.

A successful observation and analysis of the Zeeman effect on the lambda approximately 1.54 microm photoluminescence band in Er-doped crystalline MBE-grown silicon are presented. The symmetry of the dominant optically active centers is conclusively established as orthorhombic I(C(2v)) with g axially approximately 18.39 and g radially approximately 0. In this way the long standing puzzle as regards the paramagnetism of optically active Er-related centers in silicon is settled. Preferential generation of a single type of an optically active Er-related center confirmed in this study is essential for photonic applications of Si:Er.

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PubMed2002

Optically induced deexcitation of rare-Earth ions in a semiconductor matrix.

We report on verification of the proposed energy transfer mechanism responsible for photoluminescence of rare earth (RE) ions in semiconductors. Using two-color spectroscopy in the visible and the midinfrared regions (with a free-electron laser) we demonstrate reversal of the most important step in the excitation process. In that way, formation of the intermediate state bridging atomic states of the RE ion core and extended orbitals of a semiconducting host is explicitly confirmed and its characteristic energy spectroscopically determined. The study is performed for InP:Yb. It is argued, however, that the conclusions are valid for all semiconductor:RE systems, including the notorious Si:Er.

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PubMed1996