Colloidal CsPbX3 (X?=?Br, Cl, and I) perovskite nanocrystals exhibit tunable bandgaps over the entire visible spectrum and high photoluminescence quantum yields in the green and red regions. However, the lack of highly efficient blue‐emitting perovskite nanocrystals limits their development for optoelectronic applications. Herein, neodymium (III) (Nd3+) doped CsPbBr3 nanocrystals are prepared through the ligand‐assisted reprecipitation method at room temperature with tunable photoemission from green to deep blue. A blue‐emitting nanocrystal with a central wavelength at 459?nm, an exceptionally high photoluminescence quantum yield of 90%, and a spectral width of 19?nm is achieved. First principles calculations reveal that the increase in photoluminescence quantum yield upon doping is driven by an enhancement of the exciton binding energy due to increased electron and hole effective masses and an increase in oscillator strength due to shortening of the Pb?Br bond. Putting these results together, an all‐perovskite white light‐emitting diode is successfully fabricated, demonstrating that B‐site composition engineering is a reliable strategy to further exploit the perovskite family for wider optoelectronic applications.
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