Origin of Analyte-Induced Porous Silicon Photoluminescence Quenching.

We report on gaseous analyte-induced photoluminescence (PL) quenching of porous silicon, as-prepared (ap-pSi) and oxidized (ox-pSi). By using steady-state and emission wavelength-dependent time-resolved intensity luminescence measurements in concert with a global analysis scheme, we find that the analyte-induced quenching is best described by a three-component static quenching model. In the model, there are blue, green, and red emitters (associated with the nanocrystallite core and surface trap states) that each exhibit unique analyte-emitter association constants and these association constants are a consequence of differences in the pSi surface chemistries.

Instrumentation for Reliably Determining Porous Silicon Photoluminescence Responses to Gaseous Analyte Vapors.

We report new instrumentation for rapidly and reliably measuring the temperature-dependent photoluminescence response from porous silicon as a function of analyte vapor concentration. The new system maintains the porous silicon under inert conditions and it allows on-the-fly steady-state and time-resolved photoluminescence intensity and hyper-spectral measurements between 293 K and 450 K. The new system yields reliable data at least 100-fold faster in comparison to previous instrument platforms.

Pd-porphyrin-cross-linked implantable hydrogels with oxygen-responsive phosphorescence.

Development of long-term implantable luminescent biosensors for subcutaneous oxygen has proved challenging due to difficulties in immobilizing a biocompatible matrix that prevents sensor aggregation yet maintains sufficient concentration for transdermal optical detection. Here, Pd-porphyrins can be used as PEG cross-linkers to generate a polyamide hydrogel with extreme porphyrin density (≈5 × 10(-3) m). Dye aggregation is avoided due to the spatially constraining 3D mesh formed by the porphyrins themselves.

An in-depth study linking the infrared spectroscopy and photoluminescence of porous silicon during ambient hydrogen peroxide oxidation.

We carefully tailored a porous silicon (pSi) surface by oxidation with hydrogen peroxide (H2O2) to determine the time-dependent changes in nanocrystallite surface chemistries (e.g., Si-O-Si, SiH(x) [x = 1, 2], OySiH [y = 2, 3], and SiOH/H2O) and their influence on the pSi photoluminescence (PL).

Hidden Properties of Carbon Dots Revealed After HPLC Fractionation.

Carbon dots (C-dots) are often synthesized, modified, and studied as a mixture. Unfortunately, the spectroscopic and biological properties measured for such C-dots assume that there is a high degree of homogeneity in the produced sample. By means of high-resolution separation techniques, we show that "as-synthesized" C-dots exist as a relatively complex mixture and that an unprecedented reduction in such complexity can reveal fractions of C-dots with unique luminescence properties.

Link between O2SiH infrared band amplitude and porous silicon photoluminescence during ambient O3 oxidation.

We carefully evaluate how porous silicon (pSi) surface oxidation by ozone (O(3)) and the resulting changes in nanocrystallite surface chemistries (e.g., SiOSi, SiH(x) (x = 1-3), O(y)SiH (y = 1-2), and SiOH) influence the pSi photoluminescence (PL).