Cs₄PbX₆ (X = Cl, Br, I) Nanocrystals: Preparation, Water-Triggered Transformation Behavior, and Anti-Counterfeiting Application

Abstract

As a promising material, CsPbX (X = Cl, Br, I) nanocrystals (NCs) have attracted much attention. However, their luminescent property is still under debate. In this work, we first systematically studied the colloidal preparation of CsPbX NCs. It is found that the critical parameter for the formation of CsPbX NCs is the ratio between Cs and Pb. Pure CsPbX NCs are nonluminescent. The luminescence property of previous reported CsPbX NCs may come from the impurity of luminescent CsPbX NCs. No coexistence of both CsPbX and CsPbX phase has been found in one single nanoparticle. The water-triggered transformation from nonluminescent CsPbX NCs to luminescent CsPbX NCs has been quantitatively studied. The potential application of CsPbX NCs in humidity sensor and anticounterfeiting have been demonstrated. This work is important because it not only confirmed the nonluminescent nature of CsPbX NCs but also demonstrated the potential application of such NCs.

Low‐Dimensional‐Networked Cesium Lead Halide Perovskites: Properties, Fabrication, and Applications

“…For example, a hot-injection approach that employed OA and OAm as the capping ligands, and set a Cs-rich environment have been successfully used to synthesize Cs 4 PbBr 6 NCs. [22,26,[104][105][106][107] Compared to the preparation of CsPbX 3 NCs, [2] Cs 4 PbX 6 always required an excess of Cs precursor and a lower reaction temperature. Synthesis of Cs 4 PbBr 6 involved the dissolution of PbX 2 in octadecene (ODE), OA and OAm in a vial at ≈150 °C.…”

Hydrochromic CsPbBr3 Nanocrystals for Anti‐Counterfeiting

“…[17] As ar esult, they have been demonstrated to be widely used as humidity sensor,water-jetbased rewritable printing on paper,a nd anti-counterfeiting material. [17,18] One typical example is polydiacetylene (PDA) [14,16] that has been used for hydrochromic imaging. Theinkjet-printed images formed by PDAs underwent ablueto-red color transition when exposed to water, because the pconjugated PDAw as locally distorted during the process.…”

“…[24,26,27] Since metal halide perovskite materials are low-cost and of excellent luminescent properties,a ny new understanding or new findings on their smart luminescent properties may have significant influence in this field and may further lead to an innovation in their application. [18,28] Among various metal lead halide materials,a ll-inorganic CsPbX 3 has been regarded as one of the best choices for practical applications because of their higher stability than that of organic-inorganic counterparts. [29] Phase change or composition change,and as aresult, the luminescent properties change of CsPbX 3 upon different external stimuli, including water, [30,31] PbX 2 , [27,32] amines, [33][34][35] and thermal annealing, [36,37] has been demonstrated in previous reported works.H owever,i ti ss till very difficult to achieve reversible on/off of their luminescent properties.…”

Hydrochromic CsPbBr3 Nanocrystals for Anti‐Counterfeiting

“…Among various smart materials, hydrochromic ones that are responsive to water or moisture have drawn special interest because of their characteristic advantages, such as low cost, simple operation and fast response . As a result, they have been demonstrated to be widely used as humidity sensor, water‐jet‐based rewritable printing on paper, and anti‐counterfeiting material . One typical example is polydiacetylene (PDA) that has been used for hydrochromic imaging.…”

“…However, the reports on their hydrochromic property are still limited, which may be attributed to the poor stability of such perovskite materials against water, leading to the irreversibility in color or PL emission . Since metal halide perovskite materials are low‐cost and of excellent luminescent properties, any new understanding or new findings on their smart luminescent properties may have significant influence in this field and may further lead to an innovation in their application …”