Developing rare-earth element (REE) free yellow phosphors that can be excited by 455 nm blue light will help to decrease the environmental impact of manufacturing energy efficient white light-emitting diodes (WLEDs), decrease their cost of production, and accelerate their adoption across the globe. Luminescent metal-organic frameworks (LMOFs) demonstrate strong potential for use as phosphor materials and have been investigated intensively in recent years. However, the majority are not suitable for the current WLED technology due to their lack of blue excitability. Therefore, designing highly efficient blue-excitable, yellow-emitting, REE free LMOFs is much needed. With an internal quantum yield of 76% at 455 nm excitation, LMOF-231 is the most efficient blue-excitable yellow-emitting LMOF phosphor reported to date. Spectroscopic studies suggest that this quantum yield could be further improved by narrowing the material's bandgap. Based on this information and guided by DFT calculations, we apply a ligand substitution strategy to produce a semi-fluorinated analogue of LMOF-231, LMOF-305. With an internal quantum yield of 88% (λ _em = 550 nm) under 455 nm excitation, this LMOF sets a new record for luminescent efficiency in yellow-emitting, blue-excitable, REE free LMOF phosphors. Temperature-dependent and polarized photoluminescence (PL) studies have provided insight on the mechanism of emission and origin of the significant PL enhancement.

The authors have designed and synthesized a family of high-performance inorganic–organic hybrid phosphor materials composed of extended and robust networks of one, two, and three dimensions. Following a bottom-up solution-based synthetic approach, these structures are constructed by connecting highly emissive Cu4I4 cubic clusters via carefully selected ligands that form strong CuN bonds. They emit intensive yellow-orange light with high luminescence quantum efficiency, coupled with large Stokes shift, which greatly reduces self-absorption. They also demonstrate exceptionally high framework- and photostability, comparable to those of commercial phosphors. The high stabilities are the result of significantly enhanced CuN bonds, as confirmed by the density functional theory (DFT) binding energy and electron density calculations. Possible emission mechanisms are analyzed based on the results of theoretical calculations and optical experiments. Two-component white phosphors obtained by blending blue and yellow emitters reach an internal quantum yield as high as 82% and correlated color temperature as low as 2534 K. The performance level of this subfamily exceeds all other types of Cu–I based hybrid systems. The combined advantages make them excellent candidates as alternative rare-earth element-free phosphors for possible use in energy-efficient lighting devices.

Inorganic semiconductor materials are best known for their superior physical properties, as well as their structural rigidity and stability. However, the poor solubility and solution-processability of these covalently bonded network structures has long been a serious drawback that limits their use in many important applications. Here, we present a unique and general approach to synthesize robust, solution-processable, and highly luminescent hybrid materials built on periodic and infinite inorganic modules. Structure analysis confirms that all compounds are composed of one-dimensional anionic chains of copper iodide (Cu_mI_m+2^2-) coordinated to cationic organic ligands via Cu-N bonds. The choice of ligands plays an important role in the coordination mode (μ¹-MC or μ²-DC) and Cu-N bond strength. Greatly suppressed nonradiative decay is achieved for the μ²-DC structures. Record high quantum yields of 85% (λ_ex = 360 nm) and 76% (λ_ex = 450 nm) are obtained for an orange-emitting 1D-Cu₄I₆(L₆). Temperature dependent PL measurements suggest that both phosphorescence and thermally activated delayed fluorescence contribute to the emission of these 1D-AIO compounds, and that the extent of nonradiative decay of the μ²-DC structures is much less than that of the μ¹-DC structures. More significantly, all compounds are remarkably soluble in polar aprotic solvents, distinctly different from previously reported CuI based hybrid materials made of charge-neutral Cu_mX_m (X = Cl, Br, I), which are totally insoluble in all common solvents. The greatly enhanced solubility is a result of incorporation of ionic bonds into extended covalent/coordinate network structures, making it possible to fabricate large scale thin films by solution processes.