Quantum Yield Bias in Materials With Lower Absorptance
Photoluminescence (PL) quantum yield (QY), which is defined as the ratio of emitted to absorbed photons, is the central quantity that characterizes light-emitting materials. It is an important parameter to assess the light efficiency of new materials, as well as identify novel photophysical mechanisms. While QY measurements are performed as standard in research and industry, accurate measurements are challenging. Here, we show that, besides known inaccuracies, PL QY measurements exhibit a surprising systematic bias. QY values are underestimated by a factor of two or more for samples with lower absorption, which can even lead to misinterpretation of results. We combine PL QY measurements of diluted Rhodamine 6G and two different semiconductor quantum dot solutions, via the standard integrating sphere method, with analytical modeling and ray-tracing simulations and find that, independent of the setup and luminescence mechanism, all measurements suffer from the same systematic underestimation of the QY. Through statistical analysis of the measured emitted and absorbed photon numbers, we uncover the origin of this underestimation in the asymmetry of the ratio distribution for low absorption, together with setup-specific features, such as signal offsets and nonlinearities. We suggest a robust calibration procedure to correct for this bias for precise evaluation of the QY in materials used for bioimaging, biosensing, and optoelectronic or photovoltaic devices.
Bart van Dam, Benjamin Bruhn, Ivo Kondapaneni, Gejza Dohnal, Alexander Wilkie, Jaroslav Křivánek, Jan Valenta, Yvo D. Mudde, Peter Schall, and Kateřina Dohnalová.
Quantum Yield Bias in Materials With Lower Absorptance. Phys. Rev. Applied, 12(2), 2019
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The authors acknowledge Dutch STW funding (B.v.D, K.D.), FOM Projectruimte No. 15PR3230 (K.D.), Mac- Gillavry Fellowship (K.D.); projects No. 16-22092S (J.V.), No. 18-12533S (A.W.), and No. 16-18964S (I.K., J.K.) of the Czech Science Foundation; and support from the ESIF, EU Operational Programme Research, Development and Education, and from the Center of Advanced Aerospace Technology (Grant No. CZ.02.1.01/0.0/0.0/16 019/0000826), Faculty of Mechanical Engineering, Czech Technical University in Prague (G.D.). The authors would like to thank Professor T. Gregorkiewicz (University of Amsterdam) for facilitating parts of this project, S. Regli and J. Veinot (University of Alberta, Canada) for providing the high-efficiency Si QD samples, I. Sychugov (KTHRoyal Institute of Technology) for an independent control measurement, and M. Hink (University of Amsterdam) for assistance with the time-resolved measurements. Finally, access to computing and storage facilities owned by parties and projects contributing to the National Grid Infrastructure MetaCentrum provided under the program “Projects of Large Research, Development, and Innovations Infrastructures” (Grant No. CESNET LM2015042) is greatly appreciated.
B.v.D. carried out experimental measurements and analyzed the data. B.v.D., B.B., G.D., and K.D. performed simulations with the analytical model. I.K., A.W., and J.K. performed ray-tracing simulations. K.D., with Y.D.M., initiated this research and did preliminary experimental measurements. J.V. provided the independent experimental setup and analysis and initiated the use of the ray-tracing approach. P.S. and all the other authors have contributed to the final version of the manuscript.