Synthesis of a Bi³⁺-Doped Cs₂HfCl₆ Double Perovskite with Highly Efficient Blue Light Emission at Room Temperature

Lead-free perovskites have been widely studied due to their environmental friendliness and high stability. In this study, Bi³⁺-doped Cs₂HfCl₆ has been synthesized at room temperature. Different from the emission of the Cs₂HfCl₆ host (452 nm), Bi³⁺:Cs₂HfCl₆ can produce a bright blue emission at an excitation wavelength of 350 nm, which is derived from the ³P₁ → ¹S₀ transition of Bi ions and accompanied by the properties of self-trapped excitons. Moreover, 7%Bi³⁺:Cs₂HfCl₆ shows excellent stability with the photoluminescence quantum yield reaching up to 69.08%. Meanwhile, a light-emitting diode that is close to pure white light has been fabricated by using 7%Bi³⁺:Cs₂HfCl₆, which has a high color rendering index of 92.5. These results show that Bi³⁺:Cs₂HfCl₆ would be a potential candidate in the field of inorganic luminescent materials.