Eu²⁺: A suitable substituent for Pb²⁺ in CsPbX₃ perovskite nanocrystals?

Eu²⁺ is used to replace toxic Pb²⁺ in metal halide perovskite nanocrystals (NCs). The synthesis implies injection of cesium oleate into a solution of europium (ii) bromide at an experimentally determined optimum temperature of 130 °C and a reaction time of 60 s. Structural analysis indicates the formation of spherical CsEuBr₃ nanoparticles with a mean size of 43 ± 7 nm. Using EuI₂ instead of EuBr₂ leads to the formation of 18-nm CsI nanoparticles, while EuCl₂ does not show any reaction with cesium oleate forming 80-nm EuCl₂ nanoparticles. The obtained CsEuBr₃ NCs exhibit bright blue emission at 413 nm (FWHM 30 nm) with a room temperature photoluminescence quantum yield of 39%. The emission originates from the Laporte-allowed 4f⁷-4f⁶5d¹ transition of Eu²⁺ and shows a PL decay time of 263 ns. The long-term stability of the optical properties is observed, making inorganic lead-free CsEuBr₃ NCs promising deep blue emitters for optoelectronics.