Ultrafast Charge Carrier Dynamics of SnO₂ Nanoclusters:  A Refined Interpretation of the Electron−Hole Kinetics in Metal Oxides

Abstract

Femtosecond experiments on 15 nm diameter SnO2 nanoclusters measure the elementary charge carrier reactions of electron trapping and electron−hole recombination. From the early time transient absorption data, an electron-trapping time of 200 ± 20 fs is determined. In addition, an experimental scheme to determine the effect of electron thermalization on the relaxation of photoexcited electrons is presented. Excess excitation energy above the conduction band increases the decay time to 500 ± 50 fs indicating that thermalization plays an important role in the electron-trapping kinetics. The dynamics of charge carrier recombination are investigated by an ultraviolet pump intensity study. A second-order rate constant of (1.0 ± 0.3) × 10-10 cm3/s is found to fit all of the decays. The early time decay kinetics in metal oxide nanoclusters do not agree with a recently proposed fractal kinetic study but are consistent with trapped electron/free hole recombination. The assignment of the early time transient absorption at 620 nm to trapped electrons is supported by comparing the transient absorption kinetics to ground state recovery results in both SnO2 and TiO2 nanoclusters.

Ultrafast Carrier Dynamics in Exfoliated and Functionalized Calcium Niobate Nanosheets in Water and Methanol

“…Approximately 10 8 photons were absorbed per sheet in the highest fluence experiment due to the large particle size. Considering that the average nanosheet contained on the order of 10 7 NbO 6 octahedra, the exciton density was comparable to studies of metal oxide nanoparticles conducted under similar experimental conditions [39][40][41] and within the range where intensity-dependent kinetics would be expected. 36 3.3.…”

Strong Transient Absorption of Trapped Holes in Anatase and Rutile TiO2 at High Laser Intensities

“…Comparable values have been reported for the recombination rate constant by other research groups. 40,41 The absorption coefficient ratio of the transients obtained at low and high excitation conditions was 1:9, respectively, thus correlating very well with the factor used in eq 4.…”

Intraband spectroscopy and photophysics inGaSenanoparticles

“…Electron intraband transitions have been extensively studied in CdSe, [1][2][3][4][5][6] and to a lesser extent, InP nanoparticles. [7][8][9][10] The corresponding dynamics have been studied in several different types of semiconductor nanoparticles, including CdS, [11][12][13][14] PbSe, 15 SnO, 16 and several others. [17][18][19] Due to well developed synthetic methods, the most thoroughly studied type of nanoparticle is CdSe.…”