Self-Assembly of Broadband White-Light Emitters

We use organic cations to template the solution-state assembly of corrugated lead halide layers in bulk crystalline materials. These layered hybrids emit radiation across the entire visible spectrum upon ultraviolet excitation. They are promising as single-source white-light phosphors for use with ultraviolet light-emitting diodes in solid-state lighting devices. The broadband emission provides high color rendition and the chromaticity coordinates of the emission can be tuned through halide substitution. We have isolated materials that emit the “warm” white light sought for many indoor lighting applications as well as “cold” white light that approximates the visible region of the solar spectrum. Material syntheses are inexpensive and scalable and binding agents are not required for film deposition, eliminating problems of binder photodegradation. These well-defined and tunable structures provide a flexible platform for studying the rare phenomenon of intrinsic broadband emission from bulk materials

Intrinsic White-Light Emission from Layered Hybrid Perovskites

We report on the second family of layered perovskite white-light emitters with improved photoluminescence quantum efficiencies (PLQEs). Upon near-ultraviolet excitation, two new Pb–Cl and Pb–Br perovskites emit broadband “cold” and “warm” white light, respectively, with high color rendition. Emission from large, single crystals indicates an origin from the bulk material and not surface defect sites. The Pb–Br perovskite has a PLQE of 9%, which is undiminished after 3 months of continuous irradiation. Our mechanistic studies indicate that the emission has contributions from strong electron–phonon coupling in a deformable lattice and from a distribution of intrinsic trap states. These hybrids provide a tunable platform for combining the facile processability of organic materials with the structural definition of crystalline, inorganic solids

Mechanism for Broadband White-Light Emission from Two-Dimensional (110) Hybrid Perovskites

The recently discovered phenomenon of broadband white-light emission at room temperature in the (110) two-dimensional organic–inorganic perovskite (<i>N</i>-MEDA)­[PbBr₄] (<i>N</i>-MEDA = <i>N</i>¹-methylethane-1,2-diammonium) is promising for applications in solid-state lighting. However, the spectral broadening mechanism and, in particular, the processes and dynamics associated with the emissive species are still unclear. Herein, we apply a suite of ultrafast spectroscopic probes to measure the primary events directly following photoexcitation, which allows us to resolve the evolution of light-induced emissive states associated with white-light emission at femtosecond resolution. Terahertz spectra show fast free carrier trapping and transient absorption spectra show the formation of self-trapped excitons on femtosecond time-scales. Emission-wavelength-dependent dynamics of the self-trapped exciton luminescence are observed, indicative of an energy distribution of photogenerated emissive states in the perovskite. Our results are consistent with photogenerated carriers self-trapped in a deformable lattice due to strong electron–phonon coupling, where permanent lattice defects and correlated self-trapped states lend further inhomogeneity to the excited-state potential energy surface