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Lead-free double perovskite phosphors are promising alternatives to lead halide perovskites for wide uses in optoelectronic applications, but suffer from a low quantum efficiency. Here, we propose to enhance the quantum efficiency of orange-emitting Cs 2 Ag 0.4 Na 0.6 InCl 6 :Bi via a codoping strategy. The internal quantum efficiency of Cs 2 Ag 0.4 Na 0.6 InCl 6 :1% Bi phosphor was increased from 89.9% to the record 98.4 and 98.6% by codoping with 1% Ni and 1% Ce, respectively. High-level density functional theory calculations have revealed that the enhanced efficiency is ascribed to the formation of shallow trap states by codoping with Ce, while codoping with Mn can create delocalized deep traps that decrease the quantum efficiency. By applying the (Bi,Ce)-codoped sample together with a blue BaMgAl 10 O 17 :Eu 2+ phosphor, a white light-emitting diode with an excellent color rendering index of 95.7 and a correlated color temperature of 4430 K has been demonstrated. The developed Cs 2 Ag 0.4 Na 0.6 InCl 6 :Bi,Ce phosphor shows a great potential as downconversion luminescent material in solid-state lighting for general illumination.

We report the synthesis, characterization, and optical properties of three 1,3,4-oxadiazolecontaining polymers with different solubility and conjugation length (repeating units of phenylene and oxadiazole). Among them, the polymer with the shortest conjugation length (2 phenylene and one oxadiazole rings) has the widest n-n" bandgap and is not fluorescent.As a n electron-injection material, it has been successfully used to improve the quantum efficiency of polymer light-emitting diodes (LEDs) using dialkoxy derivatives of poly( 1,4-phenylenevinylene) as the electroluminescent layer and aluminum as the cathode. The second polymer, with an additional oxadiazole ring in the conjugated segment, is also an electron-injection polymer. This extra oxadiazole ring further enhances the electron transport property and has lowered the LED operating voltage more than the first polymer. The third 1,3,4-oxadiazole-containing polymer, with an even longer conjugation length, has strong blue fluorescence. Blue LEDs have been fabricated using this polymer as the electroluminescent layer, conducting polyaniline as the hole-injection layer, calcium as the cathode, and the first 1,3,4-oxadiazole-containing polymer as the electron-injection layer. These devices emitted a bright blue light, with 4.5 V of turn-on voltage and 0.1% of external quantum I -efficiency.

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