Prof. Luis F. Fonseca Profile

Prof. Luis F. Fonseca

at Univ de Puerto Rico

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Author

Publications (5)

Proceedings Article | 18 August 2005 Paper

Cathodoluminescence of modified Porous Silicon for Field Emission Displays applications

Azlin Biaggi-Labiosa, Luis Fonseca, Oscar Resto

Proceedings Volume 5929, 592916 (2005) https://doi.org/10.1117/12.615403

KEYWORDS: Silicon, Nanoparticles, Field emission displays, Electron beams, Semiconducting wafers, Raman spectroscopy, Silicon films, Ions, Nanostructures, Luminescence

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Proceedings Article | 16 July 2003 Paper

Photoluminescence and NLO study of porous silicon and nanoparticle silicon in SIO2 matrix

Huimin Liu, L. Fonseca, A. Mahfoud, O. Resto, S. Weisz

Proceedings Volume 5061, (2003) https://doi.org/10.1117/12.517341

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Optical quality porous silicon (PSi) and nanoparticle crystalline-Si (c-Si) enriched SiO₂ materials were studied by absorption; luminescence; time-resolved emission measurements. Using tunable ultrafast laser as a light source, the excited state dynamics was also investigated. In a nonlinear optical (NLO) spectroscopic study the pulsed degenerate-four-wave-mixing (DFWM) technique was employed. In absorption measurement all samples show a broad and intense UV absorption with a cut-off edge at ~400 nm. In photoluminescence (PL) measurement, red emission can generally be observed in both Psi and c-Si samples. At 8 K the broadband PL of PSi is peaked at ~670 nm, with the PL lifetime in microseconds regime. The band maximum shifts toward low energy side while excitation wavelength increases. The particle size distribution was estimated using the optical transmission data according to the size- energy gap relationship. DFWM measurement reveals a long lived, slowly decaying signal which emerges from the coherent response. It indicates that the excitation was highly localized. For c-Si sample, the luminescence maximum was found at higher energy side around 590 nm, but the emission lifetime is much shortened to as ~10ns. In order to understand the nature of nanocomposite, Eu dopant was introduced into the sample. The investigation of luminescence and time-resolved emission of Eu³⁺shows that the c-Si nanoparticles are distributed in SiO₂ matrix with an average size of the nanoparticles being around 2.2 nm. The valence band (VB) to conduction band (CB) energy gap is about 2.7 ev. By ultrashort (femtoseconds and picoseconds) laser pulse excitation the charge carriers produced in CB of c-Si nanoparticles contributes to the observed optical responses. The excited state dynamical process associated with the movement of charge carriers is characterized by an instantaneous response signal, followed by buildup of the slowly decaying signal within 500ps. The analysis of the charge creation, trapping and reactivation is discussed.

Proceedings Article | 29 April 2003 Paper

Comparative study of the growth curves of B. Subtilis, K. Pneumoniae, C. Xerosis, and E. Coli bacteria using nanometric silicon particles as a bacteriological sensor

Lilyanna Perez, Marjorie Flores, Javier Avalos, L. San Miguel, O. Resto, L. Fonseca

Proceedings Volume 5118, (2003) https://doi.org/10.1117/12.498129

KEYWORDS: Silicon, Bacteria, Particles, Nanoparticles, Sensors, Silicon films, Semiconducting wafers, Atmospheric particles, Biosensors, Luminescence

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Proceedings Article | 14 February 2003 Paper

Two-photon-excitation-induced transient valence switching in Eu-doped Si/SiO2 nanocomposites

Huimin Liu, V. Vikhnin, L. Fonseca, A. Mahfoud, G. Nery, O. Resto, Z. Weisz

Proceedings Volume 4797, (2003) https://doi.org/10.1117/12.453276

KEYWORDS: Europium, Silicon, Ions, Nanoparticles, Luminescence, Erbium, Switching, Annealing, Nanocomposites, Absorption

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Proceedings Article | 16 July 1999 Paper

Registration and fusion of multispectral images using a new control point assessment method derived from optical flow ideas

L. Fonseca, Gary Hewer, Charles Kenney, B. Manjunath

Proceedings Volume 3717, (1999) https://doi.org/10.1117/12.353029

KEYWORDS: Image fusion, Optical flow, Image registration, Multispectral imaging, Condition numbers, Reliability, Satellite imaging, Earth observing sensors, Satellites, Motion estimation

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