Thermally stimulated exciton emission in Si nanocrystals

Single-atom infrared emission in doped silicon nanocrystals

Silicon luminescence, due to silicon being abundant, non-toxic and harmless, is a topic of pivotal importance in optoelectronics and biological imaging. However, a major challenge in developing high-efficiency silicon light sources is the relatively weak allowable transitions. This study focuses on single atom-doped silicon nanocrystals (Si NCs) and theoretically investigates the emission behavior of single atoms within a tetrahedral coordination field. Doping a single atom in Si NCs can result in a ∼102 times improvement at least in the squared transition dipole moment (TDM2), and induce a spectral shift towards near- and mid-infrared wavelengths. These findings offer a strong foundation for designing Si NCs for on-chip optical communication and single photon emitters.

Low temperature radical initiated hydrosilylation of silicon quantum dots

The photophysics of silicon quantum dots (QDs) is not well understood despite their potential for many optoelectronic applications. One of the barriers to the study and widespread adoption of Si QDs is the difficulty in functionalizing their surface, to make, for example, a solution-processable electronically-active colloid. While thermal hydrosilylation of Si QDs is widely used, the high temperature typically needed may trigger undesirable side-effects, like uncontrolled polymerization of the terminal alkene. In this contribution, we show that this high-temperature method for installing aromatic and aliphatic ligands on non-thermal plasma-synthesized Si QDs can be replaced with a low-temperature, radical-initiated hydrosilylation method. Materials prepared via this low-temperature route perform similarly to those created via high-temperature thermal hydrosilylation when used in triplet fusion photon upconversion systems, suggesting the utility of low-temperature, radical-initiated methods for creating Si QDs with a range of functional behavior.

Power-dependent photoluminescence decay kinetics of silicon nanocrystals under continuous and pulsed excitation

Power-dependent photoluminescence (PL) decay kinetics of silicon nanocrystals (Si NCs) in solid and liquid samples were studied under cw and pulsed excitation. The lifetime distribution and, consequently the measured PL kinetics are shown to depend on the excitation pulse duration until it is not sufficiently short (pulsed limit) or long (cw limit). These two excitation limits, however, are proven to excite different distributions of lifetime components and cannot be directly compared. We derive and experimentally confirm the equality of lifetimes averaged over amplitude and intensity for cw and pulsed excitation, accordingly. The absorption cross section (ACS) of Si NCs in solid and liquid samples is assessed and compared by two approaches under cw-excitation based on the treatment of power-modulated PL kinetics or PL amplitude saturation curves under low and moderate excitation powers, respectively. The discrepancy in extracted ACS values as well as the long-debated phenomena of incomplete PL saturation of matrix-embedded Si NCs is explained by a proposed model that is based on saturation of various components in an ensemble distribution at different excitation powers. The model finally allows us to explain the mystery of average decay lifetime dependence on excitation power in the non-linear power regime. By varying the excitation from cw to pulsed, we showed the reduction of average decay lifetime in the later case and attribute this to the increased relative PL contribution of fast lifetime components that results in at least one order of magnitude lower ACS values. Finally, exciting the solid sample with very high excitation powers, we detected a PL intensity decrease region that allowed us to extract the Auger lifetime which is about 170 ns.

Measurement of thermal effect in laser pumped silicon employing infrared digital holographic interferometry

We present a short-coherence infrared digital holographic interferometry (IRDHI) to quantitatively measure the weak thermal effect in silicon wafer under visible laser pumping. In IRDHI, a superluminescent diode and a narrow-band filter are introduced to eliminate the self-interference fringes and suppress the noise. The effect of coherence length of the detection light source is analyzed and the optimal coherence length range in the proposed configuration is given. Meanwhile, we measure the weak thermal effect in silicon pumped by two different approaches of a continuous visible laser with different powers. The proposed configuration, which shows high stability and sensitivity, can be easily adapted and improved to measure the variation of thermal effect or refractive index in other near infrared transparent materials.