PbS/CdS Quantum Dot Room-Temperature Single-Emitter Spectroscopy Reaches the Telecom O and S Bands via an Engineered Stability

Abstract

We synthesized PbS/CdS core/shell quantum dots (QDs) to have functional single-emitter properties for room-temperature, solid-state operation in the telecom O and S bands. Two shell-growth methodscation exchange and successive ionic layer adsorption and reaction (SILAR)were employed to prepare QD heterostructures with shells of 2−16 monolayers. PbS/CdS QDs were sufficiently bright and stable to resolve photoluminescence (PL) spectra representing both bands from single nanocrystals using standard detection methods, and for a QD emitting in the O-band a second-order correlation function showed strong photon antibunching, important steps toward demonstrating the utility of lead chalcogenide QDs as single-photon emitters (SPEs). Irrespective of type, few telecom-SPEs exist that are capable of such room-temperature operation. Access to single-QD spectra enabled a direct assessment of spectral line width, which was ∼70−90 meV compared to much broader ensemble spectra (∼300 meV). We show inhomogeneous broadening results from dispersity in PbS core sizes that increases dramatically with extended cation exchange. Quantum yields (QYs) are negatively impacted at thick shells (>6 monolayers) and, especially, by SILAR-growth conditions. Time-resolved PL measurements revealed that, with SILAR, initially single-exponential PL-decays transition to biexponential, with opening of nonradiative carrier-recombination channels. Radiative decay times are, overall, longer for core/shell QDs compared to PbS cores, which we demonstrate can be partially attributed to some core/shell sizes occupying a quasi-type II electron−hole localization regime. Finally, we demonstrate that shell engineering and the use of lower laser-excitation powers can afford significantly suppressed blinking and photobleaching. However, dependence on shell thickness comes at a cost of less-than-optimal brightness, with implications for both materials and experimental design.

Colloidal 2D PbSe nanoplatelets with efficient emission reaching the telecom O-, E- and S-band

“…13,14 Additionally, colloidal lead chalcogenides are highly interesting nanomaterials for deterministic single photon emission which is applied in photonic quantum technologies like quantum key distribution. [15][16][17][18] However, synthetic access, especially to NPLs exhibiting seamlessly tunable and efficient NIR to SWIR PL is scarce. For example, Tenney et al synthesized HgTe NPLs decorated with HgTe NCs that exhibited efficient PL with a quantum yield (QY) of >30% between 1000 and 1500 nm.…”

Photon correlations probe the quantized nature of light emission from optoelectronic materials

“…Single-photon generation is particularly interesting in the IR spectral region, within the windows of minimal absorption of glass fibers as used for optical communication. 215 Both colloidal and self-assembled vapor-phase-grown quantum dots have been demonstrated as single-photon sources in this spectral region, including PbS/CdS, 220 InP/ZnSe, 221 InAs, 222 InAs/InP, 223 and InAs/GaAs quantum dots, 224 with some of these even preserving photon antibunching up to room temperature. In InAs quantumdot structures, the measurement of 𝑔 Δ𝑡 could be used to track both the photon antibunching and photon bunching effects, which appear as intensity blinking in the time traces of the luminescence.…”

Site-Controlled Telecom Single-Photon Emitters in Atomically-thin MoTe2

“…For instance, the blinking and spectral diffusion behavior of PbS quantum dots (one material capable of quantum light emission at NIR range) is wellknown. 24 We monitored the time-dependent emission using both a single-photon detector (Figure 2b, inset) and an InGaAs spectrometer (Supplementary Section S3), nding no detectable photon bleaching, blinking, or spectral diffusion over the timescales presented. Some of our MoTe 2 quantum dots were measured continuously over 24 hours and no signs of degradation were detected.…”