CAREER: Realizing next generation light-material interactions via directional, collective photoluminescence and energy transport of surface-sensitive nanocrystals

Nontechnical Description Electronic devices are everywhere, and drive increasing demands for energy. Energy-efficient devices will play an important role in addressing these needs through renewable energy generation and reduced energy consumption. One example of energy efficiency comes from light-emitting diodes (LEDs), widely used for displays and lighting. Light emitted in the forward direction escapes the device and is seen. Light emitted at a wide angle can be trapped inside the device and is wasted. Thus, controlling the direction of light emission can increase the efficiency of an LED. This CAREER project focuses on understanding the fundamental electronic and photonic processes of nanoscale materials that can exhibit highly directional light emission. Discoveries in this work could enable ultra-high efficiency lighting, displays, and solar cells. They also will provide the foundation for novel technologies such as optical computing and data storage. The investigator will also address the technological and social challenges in sustainability by training a wide range of students to be leaders in STEM. Planned activities include case study projects, undergraduate research opportunities, and a solar industry-focused Technical Academy. Technical Description The goal of this CAREER project is to understand the photophysics of cesium lead halide nanocrystals, a high-performance nanomaterial with extraordinary optical properties such as superfluorescence, single photon emission, and energy and spin funneling. The three research objectives are to correlate the tunable, directional photoluminescence to superfluorescence of these nanocrystals by studying angular lifetime; determine the limit of exciton and spin directionality in these materials; and quantify the effect of surface charge and applied voltage to the exciton transport and light emission pathways of individual nanocrystals. The research team will quantify how light and energy transport depends on the size, shape, composition, and local environment of individual nanocrystals and superlattices using an array of optical characterization techniques. Because extraordinary optical properties exhibit strong angle dependence, the research team will use time-resolved back focal plane imaging to quantify the temporal properties of light emission and energy transfer as a function of angle and momentum. The work operates at the intersection of chemical approaches to materials synthesis and surface chemistry and photonic design principles that dictate light propagation in materials, creating a perspective that will be necessary to understanding nanoscale light-matter interactions. This work will shed light on other nanomaterial systems and has the potential to enable novel quantum information technologies and optoelectronic technologies with efficiencies approaching thermodynamic limits. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.