Absolute Photoluminescence Quantum Yields of IR-26 Dye, PbS, and

pubs.acs.org/JPCL

Absolute Photoluminescence Quantum Yields of IR-26 Dye, PbS, and PbSe Quantum Dots Octavi E. Semonin,† Justin C. Johnson, Joseph M. Luther, Aaron G. Midgett,‡ Arthur J. Nozik,*,‡ and Matthew C. Beard* National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, Colorado 80401

ABSTRACT In this study, we have directly measured the photoluminescence quantum yield (ΦPL) of IR-26 at a range of concentrations and the ΦPL of PbS and PbSe QDs for a range of sizes. We find that the ΦPL of IR-26 has a weak concentration dependence due to reabsorption, with a ΦPL of 0.048 ( 0.002% for low concentrations, lower than previous reports by a full order of magnitude. We also find that there is a dramatic size dependence for both PbS and PbSe QDs, with the smallest dots exhibiting a ΦPL in excess of 60%, while larger dots fall below 3%. A model, including nonradiative transition between electronic states and energy transfer to ligand vibrations, appears to explain this size dependence. These findings provide both a better characterization of photoluminescence for nearinfrared emitters and some insight into how improved QDs can be developed. SECTION Nanoparticles and Nanostructures

for comparison measurements of the ΦPL of newly developed emitters. Many reports suggest that near-unity ΦPL values are not only possible but are easily produced in NIR emitting PbSe QDs,6 yet few direct measurements of ΦPL have been undertaken because the comparative measurement requires less instrumentation and is easier to perform. Because PbS QDs are subject to the stochastic blinking phenomena8 seen in visible emitting QDs,9 it is actually surprising that unity quantum yields are considered commonplace, further motivating our investigation of ΦPL with direct methods. Besides the fundamental scientific importance, our interest in measuring ΦPL of PbSe and PbS QDs is also motivated by our desire to use ΦPL as a tool to monitor sample quality through a variety of syntheses and treatments throughout the processing of these materials for use in photovoltaic devices.10 In this Letter, we report the ΦPL of IR-26 to be 0.05%, and we find a size-dependent ΦPL for PbSe and PbS QDs that is 60% for the smallest sizes and