Highly Luminescent and Multifunctional Zero‐Dimensional Cesium Lanthanide Chloride (Cs₃LnCl₆) Colloidal Nanocrystals

Abstract

all-inorganic ternary perovskite nanocrystals (NCs) are widely studied for their promising characteristics as semiconducting materials for optoelectronic applications owing to their high photoluminescence (PL) quantum yields (PLQYs) and narrow emission bandwidths. [3] The optical properties of perovskite NCs can be tuned by tailoring their sizes, compositions, and confined dimensions. [4][5][6][7] In addition to size confinement on the nanoscale, the dimensionality of ternary metal halides can be defined based on the arrangement of the [BX 6 ] octahedral units in the crystal structure. [8,9] Lattice distortion occurs within the metal halide structure depending on the size of the elements or the coordination number of the A cations. This induces either a two-or 1D arrangement, wherein the [BX 6 ] octahedra are linked in two directions or one direction, respectively, or complete isolation of the octahedral units (0D). [10][11][12] Among these, 0D materials have recently attracted considerable attention because their unique optical and electronic properties are distinct from those of 3D metal halide perovskite structures. [13] Specifically, 0D metal halide materials have electronically separated polyhedra or clusters resulting in a large bandgap, low conductivity, and low mobility. [8,14,15] In addition, these materials show enhanced radiative recombination owing to the self-trapping of excitons [16,17] or defects [18,19] in the spatially isolated octahedrons and broadband PL properties attributed to strong exciton-phonon coupling.Several studies have synthesized 0D metal halide structures with isolated metal halide octahedral building blocks, and their intrinsic properties have been investigated by tailoring the composition. For example, 0D Cs 4 PbBr 6 perovskites have been extensively studied because of their unique optical properties such as high PLQY, as well as high thermal, chemical, and photostabilities; however, the origin of the green emission of Cs 4 PbBr 6 is still under debate. [20][21][22][23] Lead-free 0D metal halides have also been reported, containing either main group elements, such as tin, [24,25] bismuth, [26] indium, [27] and antimony, [28] or transition metals, such as copper, [29] manganese, [30] and zinc. [31] These metal halides can be utilized as Herein, the synthesis of novel, highly luminescent, and nearly monodisperse zero-dimensional (0D) cesium lanthanide chloride (Cs 3 LnCl 6 ; Ln = Y, Ce, Gd, Er, Tm, Yb) colloidal nanocrystals (NCs) is reported for the first time. The Cs 3 LnCl 6 NCs are synthesized using a heating-up method and exhibit highly uniform size and shape. The monoclinic-phase Cs 3 LnCl 6 NCs contain completely isolated [LnCl 6 ] 3− octahedral units, resulting in 0D ternary metal halide structures. Therefore, these NCs exhibit deep-blue photoluminescence under ultraviolet excitation, and this photoluminescence can be tuned by changing the lanthanide cations within the [LnCl 6 ] 3− octahedral units. High photoluminescence quantum yields of up to 60% and 90% are observed for...

Dynamically tunable multicolor emissions from zero-dimensional Cs3LnCl6 (Ln: europium and terbium) nanocrystals with wide color gamut

“…Blue PL of 0D Cs 3 LnCl 6 (Ln: lanthanide) NCs under UV excitation have been previously reported by our group. 35 The 0D host emission from Cs 3 LnCl 6 NCs exhibit a broadband, asymmetric emission profile. In contrast, Cs 3 EuCl 6 NCs exhibit highly symmetric and very narrow PL spectra, which is inconsistent with the PL characteristic of 0D Cs 3 LnCl 6 NCs.…”

“…Colloidal Cs 3 EuCl 6 and Cs 3 TbCl 6 NCs were synthesized by the previously reported heating-up method. 35,45 The reaction was performed at 260 °C for 1 h. The reaction solution was transparent yellow before heating and turned opaque brown with europium and opaque white with terbium during the reaction, indicating the formation of NCs. As-synthesized NCs exhibit high colloidal stability in nonpolar solvents.…”

“…On the other hand, under broad band excitation from 300 to 410 nm (band 2), blue PL was observed at 430 nm PL maxima, which is similar to the PL properties of the 0D Cs 3 LnCl 6 NCs. 35 However, the characteristic green atomic emissions from f-orbitals in Tb 3+ ions coexisted. Low-temperature PL measurements showed that both blue and green PL intensity of Cs 3 TbCl 6 NCs continuously increased with decreasing temperatures (Fig.…”

“…Among the various types of metal halide NCs, lanthanide-based metal halide NCs exhibit characteristic luminescence and multifunctional properties owing to the presence of the f-block lanthanide elements. 35–38 Lanthanide elements have partially filled 4f shells, which are responsible for their characteristic optical and magnetic properties. 39,40 The sharp atomic transition between f-orbitals enables the characteristic absorption and emission bands depending on the type of lanthanide elements.…”

Deep-blue narrow-band emissive cesium europium bromide perovskite nanocrystals with record high emission efficiency for wide-color-gamut backlight displays

“…16,17 A small percentage of lead-free perovskite NCs have been found to exhibit narrow-band blue light emission. 18–22 For example, Cs 3 Sb 2 Br 9 NCs obtained through ligand-assisted reprecipitation synthesis, display a narrow full width at half maximum (FWHM) (41 nm) in the blue region. 23 Han et al reported that Cs 3 Bi 2 Br 9 NCs exhibit blue emission at 468 nm with a FWHM of 40 nm.…”