Minimizing toxicity in bright green luminescent lead doped Mn-based microcrystals

Highlights

• Lead doped Mn-based microcrystals are prepared by mechanochemical method with a Photoluminescent Quantum Yield of 30%.

• Catalytic amount of PbBr₂ is used for crystal seeding and originate the green colored emission.

• Mn-based microcrystals show better stability in solid phase over solution phase.

Abstract

The perovskite nanoparticles got much attention in research due to their interesting optoelectronic properties. The true potential application of lead-based perovskite nanoparticle has been hampered due to its toxicity and stability. This paper demonstrated a green approach for toxicity removal of lead halide perovskites to resolve their toxicological aspects using manganese-based metal halide microcrystals. Pb doped Mn-based: CH₃NH₃Mn_1-x Pb_xBr_3-yCl_y microcrystals show better stability in solid-phase over solution phase with an absolute photoluminescent quantum yield [PLQY] of 30%. All characterization has been done using ultraviolet, photoluminescence, infrared spectra, X-ray photoelectron spectroscopy, X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and thermogravimetric analysis.

Introduction

Lead halide perovskites have attracted great attention as functional materials for the high-efficiency solar cells [[1], [2], [3], [4]] color-tunable light-emitting diodes [[5], [6], [7]] photodetector [8,9] and lasers [10,11]. Recently, halide nanomaterials have been considered to exhibit narrow high efficient [12] and tunable photoluminescence [[13], [14], [15], [16], [17]] over entire visible range controlled by the composition of the nanoparticles[18]. The commercial application has been hampered due to its stability [19,20], and toxicity [21]. Doping is an effective approach to improve perovskite nanocrystals' electronic and photophysical properties [22,23]. To regulate the optical properties of lead halide perovskites, many heterovalent or isovalent metal ion such as Zn²⁺ [24], Sn²⁺[24], Cd²⁺ [24], Bi³⁺ [25], and Al³⁺ [26] were incorporated. For hybrid or inorganic perovskite substitution of lead with other transition metal have been reported [[27], [28], [29]]. Lanthanide ions are also incorporated into the lattices of CsPbCl₃ perovskite NCs through a modified hot-injection method by Xue Bai et al. [30]. Further efforts are made to prepare Mn-doped lead-based perovskite nanocrystals. David Parobek et al. also reported the one-pot synthesis of colloidal Mn-doped cesium lead halide perovskite NCs indicating that Mn could be a good choice of the substituted metal ion[31]. In this context, Liu et al. used a very high Mn: Pb ratio of precursor and shows the Mn substitution ratio was up to 46% [32]. Owing to nontoxicity, simple synthetic process, stability, and excellent luminescent property, Lead-free perovskite, is also introduced as an alternative to lead-based perovskites [33,34]. Karunadasa et al. synthesized highly moisture and thermally stable Cs₂AgBiBr₆ with a photoluminescence (PL) lifetime of 600 ns [35]. Locardi et al. Reported the first colloidal synthesis of Cs₂AgInCl₆ and Mn-doped Cs₂AgInCl₆ double perovskite nanocrytsals [36]. Recently, highly stable Manganese-doped, lead-free double halide perovskite with an excellent photoluminescent quantum efficiency (PLQE) of 44.6% has been reported by Han et al. [37]. The mechanochemical approach for the synthesis of lead doped Mn-based lead halide perovskite provides a better understanding and shows another line of hope.

In this spotlight, we have demonstrated the preparation of a high photoluminescent solid solution of Mn-based halide nanocrystals with a very trace amount of Pb dopant ratio. Besides the minimization of lead content, the as-prepared nanocrystals maintain the strong PL emission. According to the previous report [14], the PL intensity and the peak position of CH₃NH₃Mn_1-x Pb_xBr_3-yCl_y exhibit similar to MAPbBr₃ perovskites synthesized at room temperature. Lead-doped Mn-based microcrystals (d-PMC) are prepared following a similarly modified version of the previously reported synthesis of lead halide microcrystals. As described in greater detail below, molar amounts of MABr, MnCl₂, and PbBr₂ grounded in a mortar-pestle in the presence of passivating ligands like oleylamine and oleic acid at room temperature for 4 min with a rotation speed of 130–140 rotation per minutes in a 3-inch mortar. PbBr₂ is added to this solid solution to a molar ratio of 400:1, as shown in Scheme 1.