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David Hanifi1 Noah Bronstein2 Zach Nett3 Brent Koscher4 Joseph Swabeck4 Yoeri van de Burgt5 Koen Vandewal6 Alberto Salleo1 A Alivisatos4

1, Stanford, Stanford, California, United States
2, National Renewable Energy Laboratory (NREL), Golden, Colorado, United States
3, Lawrence Berkeley National Laboratory, Berkeley, California, United States
4, University of California, Berkeley, Berkeley, California, United States
5, Technische Universiteit Eindhoven, Eindhoven, , Netherlands
6, Technische Universität Dresden, Dresden, , Germany

Nanocrystals with controlled size, shape, and chemical composition can be readily synthesized and have demonstrated various new phenomena due to quantum confinement. Hierarchical assemblies of nanocrystals with different composition and sizes lead to new functionalities. With the increase in chemical precision, a need has developed for better techniques to measure photoluminescence quantum yield. Right now, the best photoluminescence measurement techniques utilize a photons-in-to-photons-out method, where the spectral sensitivity of the detector must be calibrated with a standard reference lamp, with an uncertainty budget between 2% to 10%. This makes it impossible to differentiate between a 95% quantum yield and a 100% quantum yield. Therefore, we have developed a technique called Photothermal Threshold Quantum Yield (PTQY) operates using the mirage effect, which measures the non-radiative heat produced per given photon absorbed of monochromatic light. Instead of measuring photons in and photons out, we measure heat out and photons out. The amount of heat emitted per luminesced photon can be used to determine the quantum yield without the use of any standard reference or calibrant. We will show samples of nanocrystals prepared with luminescence quantum yields well exceeding 95% measured by conventional integrating sphere techniques (2 to 10% uncertainty), compared to our PTQY measurements allowing for uncertainties less than 1%. We will also explore the meteorology and statistical analysis that allows us to approach theoretical limits of core shell nanocrystals, as well as what we can learn about crystalline defects that allow us to differentiate perfect emitters from one another.

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