In 2014 we observed white-light emission from the inorganic sheets of layered lead-halide perovskites (1). Upon UV excitation, these bulk crystalline solids emit light that spans the entire visible spectrum, similar to sunlight. These hybrid phosphors have high color rendering indices and easily tunable chromaticity coordinates. They are promising as phosphors for solid-state lighting, especially as neat large-area coatings. Recently, a number of other white-light-emitting perovskites and closely related materials have been reported, making this a burgeoning field of study (2). However, the vast majority of layered perovskites display a narrow blue/green emission, and white-light emission remains rare, leading to the question: "what is special about the white-light emitters"?
Over the past several years, we have investigated the generality of obtaining broad photoluminescence from low-dimensional metal-halide lattices. We attributed the white-light emission mechanism to exciton self-trapping, or the trapping of photogenerated electron-hole pairs in transient lattice deformations (1,3), and showed that it is common to all Pb-Br perovskites, although it is highly temperature dependent (4). I will describe our most recent work that provides a more complete picture of the emission mechanism and highlights the generality of exciton self-trapping. Our studies provide design rules for obtaining both the broad white-light emission as well as the narrow blue/green-light emission from these materials. The understanding we have developed of perovskite white-light emitters can be applied to many other low-dimensional systems.
(1) Dohner, Hoke, Karunadasa J. Am. Chem. Soc. 2014, 136, 1718 and Dohner, Jaffe, Bradshaw, Karunadasa J. Am. Chem. Soc. 2014, 136, 13154
(2) Smith, Karunadasa Acc. Chem. Res., 2018, 51, 619
(3) Hu, Smith, Dohner, Sher, Wu, Trinh, Fisher, Corbett, Zhu, Karunadasa, Lindenberg J. Phys. Chem. Lett. 2016, 7, 2258
(4) Smith, Jaffe, Dohner, Lindenberg, Karunadasa Chem. Sci. 2017, 8, 4497