All-inorganic lead-free luminescent metal halides doped with ns²-metal ions have shown great promise in next-generation solid-state lighting because of their superior optical properties and easy solution processibility.  

However, the photoluminescence (PL) origin of ns²-metal iondoped metal halides is not well understood and has been ascribed to the misconceived self-trapped exciton (STE) emission in many recent studies. Moreover, it remains challenging to achieve efficient and tunable white-light emission in metal halides due to the lack of suitable luminescent centers that allow for efficient energy transfer (ET) with minimal energy loss. 

In a study published in Angewandte Chemie International Edition, the research group led by Prof. CHEN Xueyuan from Fujian Institute of Research on the Structure of Matter of the Chinese Academy of Sciences developed a new class of highly efficient and dual-band-tunable white-light emitters based on Bi³⁺/Te⁴⁺co-doped perovskite derivative Cs₂SnCl₆ microcrystals (MCs). 

Owing to the strong electron–phonon coupling in the spatially confined 0D structure of Cs₂SnCl₆, the Bi³⁺ and Te⁴⁺ ions in the singly-doped MCs exhibited intense blue and yellow PL originating from the inter-configurational ³P_0,1→¹S₀ transitions at 456 and 565 nm with broad emission bands, large Stokes shifts, and high PL quantum yields (QYs) of 60.6% and 84.6%, respectively. 

Specifically, the researchers observed a remarkable transition in the PL lifetime from 1.20 ms at 10 K to 1.49 μs at 300 K in Cs₂SnCl₆: 1.1% Bi³⁺, due to the strong temperature dependence of the spin-forbidden ³P₀→¹S₀ and spin-orbital allowed ³P₁→¹S₀ transitions of Bi³⁺, as solid evidence for the isolated Bi³⁺ emission. 

Besides, through efficient ET from Bi³⁺ to Te⁴⁺, they realized dual-band-tunable white-light emissions in Cs₂SnCl₆: Bi³⁺/Te⁴⁺ MCs with excellent air-, structure-, photo-, and anti-water stability and a PLQY of up to 68.3%. 

This study provides new insights into both excited-state dynamics of Bi³⁺ and Te⁴⁺ in Cs₂SnCl₆ and a general approach to achieve single-composition white-light emitters based on lead-free metal halides through ns²-metal ion co-doping.