Tunable Broad Wavelength Emissions in Sn ²⁺ -Doped Zero-Dimensional All Inorganic K ₄ CdCl ₆ via Rb ⁺ Alloying

Tunable fluorescence emission endows luminescent materials with immense applications in optoelectronic devices and information security. Herein, broad-wavelength photoluminescence (PL) tuning from yellow to white to blue is realized in a zero-dimensional (0D) K 4 CdCl 6 halide via a facile Rb/Sn codoping strategy. Interestingly, K 4 CdCl 6 and isostructural Rb 4 CdCl 6 halides exhibit yellow and blue PL emissions via the homovalent doping of Sn 2+, respectively. The relative intensity ratio of yellow and blue emission bands can be effectively regulated in K 4 CdCl 6:Sn 2+ halides by Rb + alloying; accordingly, the continuous luminescence color tuning covering yellow, white, and blue spectral regions was successfully achieved. Density functional theory calculations further verify that the doping of Sn 2+ leads to the appearance of an impurity energy level within the band gap, accelerates electronic transitions, and ultimately enhances PL emission efficiency. On the basis of this rationally designed tunable luminescent system, the three-level color-coded intelligent password devices, combining multimode optical anticounterfeiting and digital information encryption, were developed. This work not only develops a reliable ion doping strategy for luminescence modulation in the metal halides but also expands their diversified application prospects in advanced optoelectronic fields.