Unusual size dependence of the optical emission gap in small hydrogenated silicon nanoparticles

Abstract

It is well known that the electronic and optical absorption gaps of hydrogenated silicon nanoparticles are inversely proportional to the particle size. Here, the authors show that their optical emission gaps are remarkably different and dully dependent on the size for those smaller than 1.5nm, based on their excited-state calculations of a series of nanoparticles from Si5H12 to Si199H140 using a time-dependent tight-binding density-functional method. It is revealed that this unusual size dependence is due to the strong excited-state structure relaxation in the particle core region that becomes significant when the size decreases.

Efficient Calculation of Electronic Absorption Spectra by Means of Intensity-Selected Time-Dependent Density Functional Tight Binding

“…Such studies have of course been performed 16,17,21,22 and while the approximations made in TD-DFTB seem drastic at first sight, the overall accuracy of the method has been found to be promising and TD-DFTB has since seen a wide variety of applications. [23][24][25][26][27][28][29][30][31][32] In summary, TD-DFTB is a computationally rather simple approximation to TD-DFT where the computational bottleneck is the size of the response matrix Ω and the calculation of its eigenvectors. In the next section we will present computational methods to solve the TD-DFTB equations efficiently.…”

Ultrafast photoluminescence dynamics of blue‐emitting silicon nanostructures

“…This approach has been recently supported by both theoretical calculations [25] and experimental results [3] which suggest a recombination in reconstructed core states of small Si NCs (< 2 nm) to be responsible for the F-band emission. Reconstruction of the core states can significantly alter the energy states structure and thus presents itself as a possible interpretation of the reported ultrafast PL dynamics.…”

Intrinsic photoluminescence of adamantane in the ultraviolet spectral region

“…Experimental results on the size dependence and magnitude of the shift due to such relaxation in Si NCs are controversial, with the maximum shift ranging from a few hundred meV to several eV. [18][19][20] Different surface structures and passivants have been predicted to exert strong influence on the Stokes shift in Si NCs. 18 For small hydrogenated Si NCs, a shift on the order of ϳ1 eV is expected due to structural relaxation of the excited state.…”

“…18 For small hydrogenated Si NCs, a shift on the order of ϳ1 eV is expected due to structural relaxation of the excited state. 18,19 Nonetheless, one has to consider that diamond nanoparticles possess a more rigid framework than their Si analogs. This rigidity should lead to less structural relaxation upon excitation and thus result in a smaller Stokes shift.…”