Cation engineering in low-dimensional organic-inorganic copper halides for high color rendering index WLEDs

Searching for single-component white-light emitting materials with excellent color rendering index (CRI) is significant to the development of white-light emitting diodes (WLEDs). Herein, we introduce three different cations with increasing steric hindrance to develop novel luminescent low-dimensional organic copper halides: one-dimensional (1D) ETMACu2I3 (ETMA: ethyltrimethylammonium), 1D TEACu2I3 (TEA: tetraethylammonium), and zero-dimensional (0D) TBMACuI2 (TBMA: tributylmethylammonium). The dimensionality of the prepared copper halides decreases with the increase of the steric hindrance of the organic cations. Meanwhile, the photoluminescence spectra become broader. The two 1D compounds exhibit weak single broad emission originating from self-trapped excitons (STEs) and defects. Interestingly, 0D TBMACuI2 emits bright warm white light with dual emission bands. The mechanism of the unique dual emission is unveiled by systematic spectroscopic study including temperature-dependent and femtosecond transient absorption spectroscopies. Two spin-triplet STE states contribute to the intriguing dual emission. A WLED based on TBMACuI2 can exhibit an ultra-high CRI of 95.7, which is promising for single-component white-light emitting applications.