Tunable Near-Infrared Optical Gain and Amplified Spontaneous Emission Using PbSe Nanocrystals

Abstract

Here, for the first time, we demonstrate amplified spontaneous emission (ASE) from PbSe nanocrystals (NCs) with emission energies tunable in the near-infrared (IR). We show that despite complications associated with a high, 8-fold degeneracy of the lowest quantized states and fast, nonradiative Auger recombination, optical gain parameters of PbSe NCs are comparable to those of CdSe NCs used for light amplification in the visible. These results indicate that previous unsuccessful attempts to realize the lasing regime in NCs of lead salts were not due to intrinsic physical reasons but likely resulted from material quality issues. By using a novel sol-gel procedure that provides both good quality surface passivation and high NC filling factors (>15%), we fabricate PbSe NC/sol-gel nanocomposites that produce ASE, which is tunable via NC size, in the near-IR. This finding indicates the feasibility of NC-based amplifiers and lasers tunable in the near-IR range and, in particular, in the range of telecommunication windows.Chemically synthesized nanocrystals (NCs) exhibit widerange size-controlled tunability of the emission color and high photoluminescence (PL) quantum yields (QYs). These characteristics make NCs attractive materials for light-emitting applications ranging from bio-labeling 1 and solid-state lighting 2 to optical amplification and lasing. 3,4 Similar to such "soft" light emitters as organic dyes and conjugated polymers, colloidal NCs offer chemical flexibility and processibility and can be easily incorporated into photonic structures or optical waveguides. 5,6 However, while organic molecules are poor infrared (IR) light emitters, III-V 7 and IV-VI 8 NCs show efficient IR emission with high, up to near-unity QYs. 9 Here, we analyze the fundamental physics of light amplification in PbSe NCs with emission energies in the near-IR. We experimentally verify that the lowest quantized states of PbSe NCs exhibit a high, 8-fold degeneracy. We find that despite this high degeneracy and fast, nonradiative Auger recombination, 10,11 PbSe NCs exhibit optical gain parameters that are similar to those of CdSe NCs, which have been shown to produce light amplification at visible wavelengths. 3 Using a novel sol-gel procedure that maintains good surface passivation and high NC filling factors, we demonstrate size-tunable ASE from PbSe NC/sol-gel nanocomposites prepared in the form of "active" planar waveguides.To date, light amplification and lasing have only been demonstrated for II-VI CdSe NCs. 3-6 However, because of the large energy gap (>1.75 eV), these NCs cannot be used for light amplification in the IR spectral range. On the other hand, tunable NC-based media capable of producing emission (see Figure 1a) and optical gain at a specific near-or mid-IR wavelength (within, e.g., telecommunication and atmospheric transparency windows) are highly desirable for a number of applications ranging from optical communications and remote sensing to a recent proposal of coherent plasmon generation. 12 Lead salts such as PbSe ha...

Active photonic devices based on colloidal semiconductor nanocrystals and organometallic halide perovskites

“…Chan et al implemented an amplifier with CdS/ZnS QDs embedded in a sol gel SiO 2 matrix pumped above 0.2 mJ/cm 2 under femtosecond excitation [57]. In addition, ASE at infrared wavelengths was achieved by incorporating PbSe QDs into a TiO 2 matrix optically pumped above 0.2 mW under picosecond excitation [58].…”

Detailed-balance power conversion limits of nanocrystal-quantum-dot solar cells in the presence of carrier multiplication

“…We approximate it by a linear growth with a slope of 1.14/ E g above the 2.85E g CM threshold and saturation at 8, 7 which corresponds to the occupancy limit of the eightfold degenerate 1S states in PbSe NQDs. 12,13 The CM phenomenon affects primarily through the short-circuit current ͑and hence, 0 ͒, but it also has a weak effect on the open-circuit voltage. The latter is influenced by CM because of the effective increase in the carrier generation rate and the potential effect of the Auger recombination, which adds a new recombination term proportional to f 1C ͑1− f 1V ͓͒f 1C + ͑1− f 1V ͔͒.…”

Carrier Multiplication in InAs Nanocrystal Quantum Dots with an Onset Defined by the Energy Conservation Limit

“…For N eh > 1, -∆R/R 0 begins to saturate at a value of ∼0.5. Saturation is typical of other NQD materials and is attributed to filling of the 1S electron state, 23,25,28 which is characterized by 2-fold degeneracy for InAs NQDs. The saturation value of |∆R/R 0 | is theoretically expected to approach 1, but often does not, possibly as a result of photoinduced absorption.…”