lead-free double perovskites of Cs 2 M(I) M(III)X 6 have drawn extensive attention and are seen as a promising alternative for LHPs. [3] The double perovskites are characterized by a 3D framework of alternating and corner-shared M(I)X 6 and M(III)X 6 octahedra. Particularly, although a great variety of double perovskites have been reported, only a few of them, such as Cs 2 NaInCl 6 , Cs 2 KInCl 6 , Cs 2 AgSbCl 6 , and Cs 2 AgBiBr 6 , have fascinating photoelectric characteristics. [4] Nevertheless, the double perovskites generally exhibit an unsatisfying photoluminescence efficiency, which is caused by their indirect bandgap characteristics or parity-forbidden transition in the direct bandgap system. [5] Hence, it is a great challenge to obtain double perovskites with highly efficient emission.Metal ion doping has been demonstrated to be a robust strategy to regulate the optical properties of LHPs, and has also achieved impressive results in double perovskites. For example, Sb 3+ doped Cs 2 NaInCl 6 shows a blue emission with a PLQY of 75.89%, [6] Sb 3+ doped Cs 2 KInCl 6 emits a cyan emission with a PLQY of 99.2%, [7] Bi 3+ doped Cs 2 (Ag 0.6 Na 0.4 )InCl 6 shines white emission with a PLQY of 86%, [8] Mn 2+ doped Cs 2 Na 0.2 Ag 0.8 InCl 6 shows a red emission with a PLQY of 32%. [9] Although single-doping technology of double perovskites can achieve efficient emission in the visible light range and has made significant progress in solid-state lighting (SSL), its further development is undoubtedly limited by its un-tunable emission and single scope of application. Recent works have suggested that co-doping strategy can provide multiple emission centers in a single compound, which endows double perovskites to have abundant optical properties, and can further develop its applications in multifunctional materials. For instance, Bi 3+ /Sb 3+ co-doped Cs 2 Ag 0.1 Na 0.9 InCl 6 exhibits a distinct excitation-wavelength dependent emission characteristic, which makes it show great potential in optical anti-counterfeiting. [10] More particularly, ns 2 metal ions (M 3+ = Bi 3+ and Sb 3+ ) can work as a sensitizer of Ln 3+ (Ln = Yb, Er, Nd), and construct an appropriate energy-transfer channel from ns 2 electrons to Ln 3+ , thus ultimately boosting the nearinfrared emission (NIR) of Ln 3+ . [11] Typical examples are that the NIR emission intensity of Bi 3+ /Er 3+ and Bi 3+ /Yb 3+ co-doped Cs 2 AgInCl 6 is about 45 and 27 times higher than that of single Recently, ns 2 metal ions (such as Bi 3+ and Sb 3+ ) doped double perovskites have captured intense attention for their efficient emission, however, achieving efficient and tunable white light emission is always an enormous challenge. Herein, Sb 3+ /Ho 3+ co-doped Cs 2 KInCl 6 double perovskites are proposed, and the photoluminescence results show that there are two emission bands, one broad cyan emission band stems from self-trapped exciton (STE) in [SbCl 6 ] 3octahedron, while another red emission band derives from the f-f transitions of Ho 3+ . The emission processes ...

Long afterglow luminescent materials have captured intense attention for their unique applications in biological imaging, photodynamic therapy, and optical anti-counterfeiting. However, achieving highly efficient and tunable ultralong afterglow emission in all-inorganic metal halides is an open challenge. Herein, Sb 3+ -doped hexagonal CsCdCl 3 metal halide is reported via hydrothermal reaction. Upon photoabsorption, the as-synthesized compounds exhibit dual-emission bands with a photoluminescence quantum yield (PLQY) of 59.6%, which can be attributed to the self-trapped exciton emission out of the strong electron-phonon coupling. After ceasing excitation of 365 nm, bright afterglow emission with the longest duration lasting up to 5000 s is witnessed in Sb 3+ -doped CsCdCl 3 . More importantly, the color-tunable and time-dependent ultralong afterglow emission is realized via regulating the doping concentration of Sb 3+ , which should be due to the trap electrons increase gradually under high doping concentration. Given this unusual afterglow emission characteristics, the optical anti-counterfeiting and information encryption are constructed based on as-synthesized compounds. These findings not only help further understand the tunable afterglow emission mechanism in all-inorganic metal halides, but also provide a new strategy for designing novel ultralong afterglow luminescent materials.