Colloidal lead halide perovskite nanocrystals (NCs) have high tunability in the visible light region and high photoluminescence quantum yields (PL QYs) for green and red emissions, but bright blue emission is still a challenge. Super small CsPbBr3 perovskite NCs emit blue light around 460 nm with a narrow peak width, and they do not have the problem of phase separation like their Cl–Br counterparts. However, the blue emission from super small CsPbBr3 NCs easily becomes green over time, and their PL QY is still low. The doping of Sb3+ ions successfully reduced the surface energy, improved the lattice energy, passivated the defect states below the band gap, eventually boosted the PL QY of blue emission to 73.8%, and resulted in better spectral stability even at elevated temperatures in solution (40–100 °C). Its CIE coordinates were (0.14, 0.06), which are close to the primary blue color (0.155, 0.070) according to the NTSC TV color standard.

Carbon quantum dots (C‐QDs) show potential to replace traditional semiconductive quantum dots as the next generation of fluorescent probes. We demonstrate here a new C‐QD production process using lignin, a high‐volume but low market‐value industrial waste and/or environmental hazards, as the starting carbon source. By adding a small amount of inorganic acid, the rich phenolic components in lignin were successfully converted to C‐QDs through a coking formation mechanism similar to what happens on solid acid catalysts in traditional fossil fuel cracking process. Their aqueous solution presence of the received lignin C‐QDs is beneficial for brain cell imaging applications, attributing to their fast internalization, low toxicity, tunable photoluminescence by appropriate acidity and reaction temperature during hydrothermal synthesis. This method not only provides a low‐cost C‐QDs production route, but also helps gain extra profit and/or improve environment for many small agricultural business and paper and pulp industry located in rural area.

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