Tunning Multicolor Light Emission in Lead-free Materials

Abstract: Lead-based perovskites, a class of ceramic oxides with general molecular formula of ABX3, are becoming increasingly attractive recently due to various advantages such as abundant raw materials, easy synthesis, excellent photoelectric properties, and short production process. As one of the applications for lead-based perovskites, the perovskite solar cells have quickly improved their power conversion efficiency from 3.8% in 2009 to over 25% within a short period. However, the problems, such as instability of the ionic crystal nature and toxicity of lead, largely hinder the lead-based perovskites towards commercialization. Therefore, it is necessary to develop new lead-free materials as alternative to lead-based perovskites, where similar structures can be formed to inherit the excellent optoelectronic properties. Moreover, new properties can be achieved due to more abundant metal candidates in lead-free materials. Based on this, we develop different kinds of perovskite-structure-like lead-free materials such as organic inorganic hybrid materials, chiral materials and double perovskites. In addition to physical and chemical properties like photoluminescence, absorption, structure, etc., we further demonstrate their potential applications according to their unique properties such as multicolor light emission.We incorporate chiral MBABr (Bromide methylbenzylamine) into the inorganic frame to obtain chiral lead-free organic inorganic hybrid materials, where we observe significant crystallization difference between resulting racemic and chiral metal halide composites for the first time. Such difference is confirmed by both structural and spectroscopic measurements. In addition, we find that the structural transformation in chiral composites can also be induced by moisture, ascribed to the asymmetric hydrogen-bonding in chiral materials. Our results provide new insights for future synthesis of chiral materials and open up new possibilities to advance our materials functionalities.Then, we successfully achieve blue luminescence center in Mn-based organic and inorganic composites through selecting specific organic component methylbenzylamine (MBA). Our approach is fundamentally different from green and red emission in Mn-based composites, which result from Mn-halide frameworks. The coexistence of different luminescence centers in our Mn-based composites is confirmed by photoluminescence (PL) and PL excitation (PLE) results. As a result of different PLE responses of different emission centers, the resulting emission color can be tuned with selecting different excitation wavelengths. Specifically, a white light emission can be obtained with Commission Internationale de l'éclairage (CIE) coordinates of (0.33, 0.35) upon the 330 nm excitation. We further demonstrate the promise of our Mn-based composites in the anti-counterfeiting technology and multicolor lighting. Our results provide a novel strategy for full-spectral emission in Mn-based OIMHs and lay a solid foundation for a range of new applications.We finally obtained Sb3+/Cu+ co-doped Cs2NaInCl6 (CNIC) double perovskite by hydrothermal reaction which exhibits tunable dual emissions with PL quantum efficiency (PLQE) of 78%. Depending on different photoluminescence excitation (PLE) spectra between two emissions, multiple emission colors can be achieved by changing excitation wavelength. Interestingly, the emission color gamut can be further tuned through manipulating the feeding ratio of CuI dopant, where warm color and cool color can be achieved separately. We further demonstrate the promise of our co-doped materials in the anti-counterfeiting technology and multicolor lighting devices. Our results provide a novel strategy for wider spectral emission in double perovskites and lay a solid foundation for a range of new applications.