Enhanced quantum yield of photoluminescent porous silicon prepared by supercritical drying

Abstract

The effect of supercritical drying (SCD) on the preparation of porous silicon (pSi) powders has been investigated in terms of photoluminescence (PL) efficiency. Since the pSi contains closely spaced and possibly interconnected Si nanocrystals (<5 nm), pore collapse and morphological changes within the nanocrystalline structure after common drying processes can affect PL efficiency. We report the highly beneficial effects of using SCD for preparation of photoluminescent pSi powders. Significantly higher surface areas and pore volumes have been realized by utilizing SCD (with CO2 solvent) instead of air-drying. Correspondingly, the pSi powders better retain the porous structure and the nano-sized silicon grains, thus minimizing the formation of non-radiative defects during liquid evaporation (air drying). The SCD process also minimizes capillary-stress induced contact of neighboring nanocrystals, resulting in lower exciton migration levels within the network. A significant enhancement of the PL quantum yield (>32% at room temperature) has been achieved, prompting the need for further detailed studies to establish the dominant causes of such an improvement.

Si/SiO2 Core/Shell Luminescent Silicon Nanocrystals and Porous Silicon Powders With High Quantum Yield, Long Lifetime, and Good Stability

“…The peak intensity was similar to that of HWA-SiNCs, but The FWHM was much smaller. The value, 137 nm, falls within the lower end of the typical values found for PSi layers [12,14,23,40].…”

“…The method is conventional and was also used by others. For instance, Jurbergs et al [2] used a LED-380 with a USB2000 spectrometer and Joo et al [14] used a LLS-365 with a QEPro spectrometer. In our case, the spectrometer's spectral response was calibrated with calibration lamp (Ocean Optics HL-2000-CAL-INT) in the 350-1,100 nm spectral range.…”

“…Luminescent Si nanocrystals (SiNCs) are intensively studied for their potential applications in diverse fields, such as optoelectronics, sensing, and medicine [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Some particularly important characteristics of such SiNCs include absolute quantum yield (AQY), stability, luminescence lifetime, surface chemistry, and synthesis route.…”

“…AQY of 23% was reported with PSi layers treated by high-pressure water vapor annealing (HWA) [26,27] and with PSi powders modified by solution-based chemical oxidation [28]. Recently, ∼32% was reported [14], for most likely hydrogen-terminated PSi dried using a supercritical process. Hydrogen-terminated PSi is generally unstable due to the high reactivity of H-Si bonds.…”

Tracking the Fate of Porous Silicon Nanoparticles Delivering a Peptide Payload by Intrinsic Photoluminescence Lifetime

“…A spectrometer fitted with an intensified charge‐coupled device (CCD) detector was used to capture PL spectra in 10 µs increments after a pulse of incident UV excitation (Figure d,e and Figure S1, Supporting Information). Consistent with previous results, the emission decays of the PSiNPs were slower at the longer wavelengths . The time‐resolved emission spectrum can yield the excited state lifetime for emission, τ, which is inversely proportional to the sum of the radiative and nonradiative decay constants (see Supplemental Discussion S1 in the Supporting Information) .…”