Here, a new type of Sb 3+ /Sm 3+ ions heavy concentration doped Cs 2 NaBiCl 6 double perovskites was successfully synthesized by solvothermal route. The downshifting photoluminescence properties of all samples are analyzed in detail, and the luminescence mechanism is further elucidated by fluorescence decay lifetime. Upon excitation at 354 nm, a strong blue emission band(400–500 nm) is observed for Cs 2 NaBiCl 6 :Sb 3+ , which comes from self-trapping exciton(STE) recombination of distorted [SbCl 6 ] 3– . Benefiting from Sb 3+ -induced local structural modification and narrow optical band gap, both STE broadband and Sm 3+ ions visible luminescence emissions are significantly boosted through free exciton(FE) sensitization in Cs 2 NaBiCl 6 :Sb 3+ /Sm 3+ sample. In addition, the luminescence thermal performances of Cs 2 NaBiCl 6 :Sb 3+ /Sm 3+ sample are investigated from 93 to 293 K. The luminescence thermal enhancement phenomenon is obtained at lower temperature range. The optical temperature sensing performance is discussed with luminescence intensity ratio technique, with maximum relative sensitivity of 5.676 % K −1 at 213 K. Finally, the anti-counterfeiting application of Cs 2 NaBiCl 6 :Sb 3+ /Sm 3+ sample is elaborated due to their bright multi-color emission under different excitation and temperature.
Tongxuan Mi,Yuhong Zhang,Luo Su,Jingyi Zhang,Jingliang Zhang,AoTian Zhang,Hang Liu
In this paper, a series of Sm 3+ single-doped and Sm 3+ /Er 3+ co-doped lead-free double perovskite cesium sodium bismuthate hexachloride(Cs 2 NaBiCl 6 ) fluorescent materials are successfully synthesized by solvothermal method, and their multimode luminescence properties and temperature sensing properties are systematically studied. The yellow, orange and green tunable luminescence of Cs 2 NaBiCl 6 :Sm 3+ /Er 3+ phosphor are achieved by adjusting the excitation wavelength(380, 410, 980 nm). The material exhibits multi-color luminescence characteristics under different excitation. Moreover, the anti-counterfeit design exhibits robust security and resistance to duplication. Based on the luminescence intensity ratio(LIR) technology, the relative sensitivity(S R ) of Cs 2 NaBiCl 6 :15 %Sm 3+ /20 %Er 3+ reaches 3.06 %K −1 (313 K) under 410 nm excitation. The study provides a new idea for the development of multi-functional lead-free perovskite materials in the field of optical anti-counterfeiting and precision temperature measurement.
Self-trapped excitons are prevalent in metal halide perovskites (MHPs) characterized by soft lattices and strong exciton-phonon coupling, emitting photons with broadband emission and large Stokes shifts, rendering them particularly well-suited for applications in light-emitting diodes. But their photoluminescence quantum yields (PLQY) are limited by both high exciton binding energy and halogen-vacancy-associated non-radiative recombination. Here, we show that PLQY could be enhanced by a factor of 5.6 from 16% to 89% through doping trace Ag into Cs 2 NaBiCl 6 double perovskites, superior to those of previous Cs 2 NaBiCl 6 -based emitters. Experimental and theoretical studies reveal that trace Ag-initiated covalent interactions could reduce the exciton binding energy by 0.12 eV due to local symmetry breaking, thus improving the photoexcitation process. Also, this covalent interaction could passivate Cl vacancy defects, suppressing non-radiative recombination. Therefore, Cs 2 NaBiCl 6 : 0.7% Ag + could accumulate active self-trapped excitons to obtain high PLQY. Assembly of near-infrared light-emitting diodes using Cs 2 NaBiCl 6 : 0.7% Ag + illustrates their valuable applications in nondestructive spectral analysis and night vision illumination. This work shows an effective strategy of improving photoemission of MHPs with high PLQY for advanced optoelectronic applications.
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