Up until now, the applications of lanthanide ion-doped lead-free double perovskite Cs2AgInCl6 nanocrystals (NCs) have been rarely reported, especially in fluorescence anticounterfeiting and coding. Here, we successfully incorporated Tb3+/Ho3+ ions into Cs2AgInCl6 NCs by the hot-injection method. Benefiting from the energy transfer process, Tb3+- and Ho3+-codoped Cs2AgInCl6 NCs showed tunable emission color in a green-blue-orange triangle region. Combining our NCs with transparent ink for printing, we put forward the applications of color bar codes and color QR codes (3D codes) as well as information encryption. Compared with traditional codes, color bar codes and 3D codes conquer the shortcomings of low information density, weak information security, and poor aesthetics. Furthermore, through double-mode excitation, we list an encoding table corresponding to 26 letters and 10 numbers. The encoding table embodies the application value of information encryption and coding.
In this study, a facile approach is used to enhance the broad orange emission efficiency and stability as well as monodispersity of Cs2AgInCl6 nanocrystals (NCs) via doping Bi3+ and surface passivation with potassium bromide. While the pristine Cs2AgInCl6 NCs show an excitonic absorption peak at 280 nm, the doped NCs have an additional absorption peak at 365 nm, which is attributed to direct bismuth s–p transition. Compared to the low photoluminescence (PL) quantum yield (QY) of 0.04% for the pristine Cs2AgInCl6 NCs due to parity forbidden transition, the doped NCs show a PLQY of 5.82%, a significant improvement due to breaking of the parity forbidden transition. The PLQY can be further increased to 8.59% for Cs2AgIn0.9Bi0.1Cl6 when passivated with KBr. This work demonstrates that the combination of doping and surface passivation can substantially improve the PL of the Cs2AgInCl6 double perovskite. A model is proposed to explain the observed enhancement in PL and stability.
Shixun Wang,Jinsong Qi,Stephen V. Kershaw,Andrey L. Rogach
Lead-free double cation metal halide perovskites have recently attracted considerable attention, with continuing research efforts focusing on the improvement of their stability and photoluminescence quantum yield (PL QY). In this study, Ce3+ has been co-doped together with Bi3+ into lead-free double perovskite Cs2AgInCl6 nanocrystals (NCs) in order to improve their crystallinity and PL QY. Both uncoordinated chloride ions and silver vacancies could be eliminated using this co-doping strategy, and the resulting Ce3+,Bi3+-co-doped Cs2AgInCl6 NCs showed adjustable PL emission peaks in the range of 589 to 577 nm by varying the doping amount of Ce3+ with a fixed feeding ratio of bismuth precursor set at 1%. Cs2AgInCl6 NCs doped with 1% Bi alone reached a PL QY of 10% for the PL peak centered at 591 nm, while those co-doped with 1% Bi and 2% Ce together achieved the highest PL QY of 26% for the PL peak centered at 580 nm. The use of Ce3+ as a dopant promoted the localization of self-trapped excitons to prevent PL quenching, although the ion’s 5d excited state may potentially provide an energetically favorable indirect route for the radiative relaxation process. This also resulted in a blue shift of the PL maximum and increased the exciton binding energy, thus promoting the radiative recombination of self-trapped excitons.
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