Tunable Dual Emission in Bi³⁺/Te⁴⁺-Doped Cs₂HfCl₆ Double Perovskites for White Light-Emitting Diode Applications

Multicolor-emission-based single-phase white light derived from different luminescence centers is an effective way to manipulate the optical properties of halide perovskites. In this work, we developed a codoping strategy to incorporate Bi³⁺ and Te⁴⁺ emission centers into all-inorganic lead-free Cs₂HfCl₆ perovskite by a hydrothermal method. The as-prepared Bi³⁺/Te⁴⁺-doped Cs₂HfCl₆ microcrystals show bright blue (Bi³⁺), yellow (Te⁴⁺), and warm-white emissions (Bi³⁺/Te⁴⁺), respectively. The broad efficient dual emission in Bi³⁺/Te⁴⁺ co-doped Cs₂HfCl₆ is assigned to the typical ³P₁ → ¹S₀ transition emission from Bi³⁺ originating from [Bi_Hf + V_Cl] and self-trapped excitons (STEs) from Te⁴⁺. Moreover, the concentration-optimized Cs₂HfCl₆:Te⁴⁺ shows excellent antiwater stability and high photoluminescence quantum yield (PLQY) of ∼70%. Meanwhile, a white light-emitting diode (WLED) fabricated using Bi³⁺/Te⁴⁺ co-doped Cs₂HfCl₆ is close to warm white with a color rendering index (CRI) of 75.4, CIE color coordinate of (0.370, 0.393), and a correlated color temperature (CCT) of 4380 K. These results suggest that Bi³⁺/Te⁴⁺ co-doped all-inorganic lead-free Cs₂HfCl₆ is a potential single-phase white light-emitting phosphor candidate for solid-state lightings.