4 research outputs found
The Dominant Role of Exciton Quenching in PbS Quantum-Dot-Based Photovoltaic Devices
We
present a quantitative measurement of the number of trapped
carriers combined with a measurement of exciton quenching to assess
limiting mechanisms for current losses in PbS-quantum-dot-based photovoltaic
devices. We use photocurrent intensity dependence and short-wave infrared
transient photoluminescence and correlate these with device performance.
We find that the effective density of trapped carriers ranges from
1 in 10 to 1 in 10 000 quantum dots, depending on ligand treatment,
and that nonradiative exciton quenching, as opposed to recombination
with trapped carriers, is likely the limiting mechanism in these devices
Measurement of Emission Lifetime Dynamics and Biexciton Emission Quantum Yield of Individual InAs Colloidal Nanocrystals
The
understanding of the photophysics of visible-emitting colloidal
nanocrystals (NCs) has long been aided by single-molecule studies
of their emission. Until recently, no suitable detection technologies
have existed for corresponding studies of shortwave-infrared (SWIR)
emitters. Now, the use of superconducting nanowire single-photon detectors
(SNSPDs) enables the detailed study of SWIR NC emission dynamics at
the single-emitter level. Here, we report a detailed analysis of the
emission dynamics of individual InAs/CdZnS NCs emitting in the SWIR
region. We observe blinking akin to the type A and type B blinking
previously observed in visible-emitting CdSe NCs. We determine the
intrinsic radiative lifetime of several InAs/CdZnS NCs and find examples
ranging from 50–200 ns, indicative of a quasi-type-II electronic
structure. We also measure <i>g</i><sub>0</sub><sup>(2)</sup> for several of these NCs and
find that their biexciton emission quantum yields vary from <1%
up to 43%
Efficient Single Photon Detection from 500 nm to 5 μm Wavelength
We report on superconducting nanowire single photon detectors
(SNSPDs)
based on 30 nm wide nanowires with detection efficiency η ∼
2.6–5.5% in the wavelength range λ = 0.5–5 μm.
We compared the sensitivity of 30 nm wide SNSPDs with the sensitivity
of SNSPDs based on wider (85 and 50 nm wide) nanowires for λ
= 0.5–5 μm. The detection efficiency of the detectors
based on the wider nanowires became negligible at shorter wavelengths
than the 30 nm wide SNSPDs. Our 30 nm wide SNSPDs showed 2 orders
of magnitude higher detection efficiency (η ∼ 2%) up
to longer wavelength (λ = 5 μm) than previously reported.
On the basis of our simulations, we expect that by changing the optical
coupling scheme and by integrating the detectors in an optical cavity,
the detection efficiency of our detectors could be increased by a
factor of ∼6
Single Photon Counting from Individual Nanocrystals in the Infrared
Experimental restrictions imposed on the collection and
detection
of shortwave-infrared photons (SWIR) have impeded single molecule
work on a large class of materials whose optical activity lies in
the SWIR. Here we report the successful observation of room-temperature
single nanocrystal photoluminescence at SWIR wavelengths using a highly
efficient multielement superconducting nanowire single photon detector.
We confirm that the photoluminescence from single lead sulfide nanocrystals
is strongly antibunched, demonstrating the feasibility of performing
sophisticated photon correlation experiments on individual weak SWIR
emitters, and, more broadly, paving the way for sensitive measurements
of spectral observables on infrared quantum systems that are incompatible
with current detection techniques