| Summary: | Abstract Colloidal nanocrystals (NCs) can be used to prepare high-color-purity metal halide perovskites (MHPs) for light-emitting displays. However, the NCs have a finite particle-size distribution, which broadens the linewidth of photoluminescence spectra under strong quantum confinement, and thereby degrades the color purity of the MHPs. This paper presents a simple method to quantify this externally-introduced broadening of linewidth $${{{{{{\boldsymbol{\Gamma }}}}}}}_{{{{{{\bf{SD}}}}}}}$$ Γ SD by combining experimental size-distribution histogram with size-dependent photoluminescence-wavelength (PL- $${{{{{\boldsymbol{\lambda }}}}}}$$ λ ) curve. We develop a semi-empirical method to estimate the other three contributions to the experimentally-measured full-width at half-maximum, $${{{{{{\boldsymbol{\Gamma }}}}}}}_{{{{{{\bf{EXP}}}}}}}$$ Γ EXP . Namely: the intrinsic linewidth $${{{{{{\boldsymbol{\Gamma }}}}}}}_{{{{{{\bf{LO}}}}}}}$$ Γ LO caused by exciton-longitudinal optical (LO) phonon Fröhlich coupling; the inhomogeneous linewidth $${{{{{{\boldsymbol{\Gamma }}}}}}}_{{{{{{\bf{o}}}}}}}$$ Γ o caused by imperfections-related scattering, and the broadening $${{{{{{\boldsymbol{\Gamma }}}}}}}_{{{{{{\bf{QC}}}}}}}$$ Γ QC due to the quantum-confinement effect. We show that $${{{{{{\boldsymbol{\Gamma }}}}}}}_{{{{{{\bf{LO}}}}}}}$$ Γ LO of a nanocrystal decreases together with the particle size, disappearing at 1.6 nm radius. Finally, we show that $${{{{{{\boldsymbol{\Gamma }}}}}}}_{{{{{{\bf{LO}}}}}}}$$ Γ LO is correlated with the degree of Fröhlich-polaron formation, hence proportional to the long-range LO-phonon-electron coupling.
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