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Measurement of Two‐Photon Absorption of Silicon Nanocrystals in Colloidal Suspension for Bio‐Imaging Applications
Author(s) -
Furey Brandon J.,
Silbaugh Dorothy A.,
Yu Yixuan,
Guillaussier Adrien C.,
Estrada Arnold D.,
Stevens Christopher,
Maynard Jennifer A.,
Korgel Brian A.,
Downer Michael C.
Publication year - 2018
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.201700501
Subject(s) - absorption (acoustics) , two photon excitation microscopy , chemistry , wavelength , two photon absorption , rhodamine b , excitation , suspension (topology) , fluorescence , optoelectronics , materials science , analytical chemistry (journal) , optics , laser , physics , biochemistry , mathematics , chromatography , photocatalysis , quantum mechanics , homotopy , pure mathematics , composite material , catalysis
Two‐photon absorption (2PA) of ligand‐passivated silicon nanocrystals (ncSi) in liquid suspensions is difficult to measure directly because of their low 2PA cross section and competing nonlinear optical processes in the suspension medium at high light intensity. Here we overcome these difficulties for small (diameter d < 5 nm) ncSi by measuring background‐free, 2PA‐induced photoluminescence (PL) at intensities below the threshold for high‐order processes, and at wavelengths shorter than the excitation wavelength λ (2) = 810 nm. We calibrate the instrument response by measuring PL induced by one‐photon absorption, and confirm previously reported 2PA cross sections σ (2) for a control rhodamine B dye solution. We find σ (2) = (0.28 ± 0.05, 1.25 ± 0.17, and 18 ± 3) × 10 −50 cm 4 s/photon, respectively, for d = 2.0, 2.6, and 5.1 nm diameter ncSi suspended in toluene. For d = 5.1 nm ncSi, the PL spectrum overlaps λ (2) , and PL scales sub‐quadratically with intensity at lower intensities in our range, indicating one‐photon excitation of the upper PL level. Thus the indirect method reported here appears best suited for ncSi with d < 5 nm. 2PA confocal microscopy of mouse cells incubated with d = 2.7 nm ncSi is demonstrated.