Zero-dimensional (0D) metal halides are in a blossoming status for their fascinating optoelectronic properties. Herein, an antimony-based metal halide of (C16H28N)2SbCl5 (C16H28N+ = benzyltripropylammonium cations), where the isolated [SbCl5]2− clusters are surrounded by C16H28N+ to form a 0D square-pyramidal structure, was synthesized and investigated. The (C16H28N)2SbCl5 exhibited a broadband orange emission at 633 nm upon the low-energy irradiation (400 nm) with a near-unity photoluminescence quantum efficiency (97.8%). Interestingly, (C16H28N)2SbCl5 showed an additional emission peak at 477 nm upon the higher-energy irradiation (300 nm), which is attributed to the transformation of the doublet of spin-orbit couplings into two independent self-trapped excitons (STEs). Temperature-dependent Raman spectra clearly revealed the characteristics of multi-phonon coupling, demonstrating a strong anharmonic electron-phonon interaction in (C16H28N)2SbCl5. Temperature-dependent emission spectra and density functional theory results illustrated that the observed dual-band emission originated from singlet and triplet STEs in [SbCl5]2− units. Combined with the efficient emission and excellent stability of (C16H28N)2SbCl5, a stable white-light-emitting diode with an ultra-high color rendering index of 96.6 was fabricated. 

https://link.springer.com/content/pdf/10.1007/s40843-021-1937-y.pdf

(C16H28N)2SbCl5: A new lead-free zero-dimensional metal-halide hybrid with bright orange emission

Controlling the structure of halide perovskites through component engineering, and thus revealing the changes in luminescence properties caused by the conversion of crystal structure, is of great significance. Herein, we report a controllable synthetic strategy of three-dimensional (3D) Cs2KInCl6 and zero-dimensional (0D) (Cs/K)2InCl5(H2O) halide perovskites by changing the Cs/K feed ratio. 3D Cs2KInCl6 double perovskites are obtained at the Cs/K feed ratio of 1:1, while 0D (Cs/K)2InCl5(H2O) perovskites are formed at the Cs/K feed ratio of 2:1. Further, a reversible crystal structure transformation between 3D Cs2KInCl6 double perovskites and 0D (Cs/K)2InCl5(H2O) perovskites can be achieved by subsequent addition of metal-salt precursors. In addition, the emission efficiency of two perovskite structures can be greatly boosted by breaking the forbidden transition through Sb doping, and as a result, a novel green/yellow reversible emission switch is generated. Meanwhile, the relationship between perovskite structure and luminescence mechanism has been systematically revealed. These environmentally stable halide perovskites have great potential to be applied in optoelectronic devices.

Component Engineering to Tailor the Structure and Optical Properties of Sb-Doped Indium-Based Halides.

Hybrid metal halides are an emerging class of highly efficient photoluminescent (PL) materials. However, very few of them show reversible on–off PL switching under external stimuli and have the potential to perform as next-generation intelligent materials with applications in cutting-edge photoelectric devices. Herein, we report single crystal-to-single crystal (SC–SC) structural and PL transitions among three 0D hybrid antimony halides, namely, nonemissive α-[DHEP]SbCl5 (1), yellow-emissive β-[DHEP]SbCl5·2H2O (2), and red-emissive β-[DHEP]SbCl5 (3), by a dynamic phonon-engineering strategy. The reversible SC–SC transformation between 1 and 2 is triggered by acetone or methanol, affording the reversible PL on–off switching. The transition between yellow-emissive and red-emissive solids is achieved by the reversible SC–SC transformation between 2 and 3 through the process of removal/adsorption of guest water molecules. Meanwhile, the 3 to 1 transition is performed by the introduction of methanol, which is accompanied by the quenching of red emission. Therefore, a triple-mode reversible PL off–onI–onII–off switching is realized in metal halide hybrids for the first time, including the off–onI (yellow), color-tunable onI–onII (yellow-red), and onII–off (red) modes. More importantly, the reversible PL switching in 0D hybrid antimony halides make them suitable for successful applications in the protection and anti-counterfeiting of confidential information as well as in optical logic gates. 

Reversible Triple-Mode Switching in Photoluminescence from 0D Hybrid Antimony Halides

0D Mn 2+ -based bromides with [MnBr 4 ] 2− tetrahedral and [Mn 3 Br 12 ] 6− octahedral units are designed, which aims at clarifying the relationship between the coordination units of Mn 2+ and tunable emissions. 

Coordination units of Mn<sup>2+</sup> modulation toward tunable emission in zero-dimensional bromides for white light-emitting diodes

Metal halide perovskites have flexible crystal and electronic structures and adjustable emission characteristics, which have very broad applications in the optoelectronic field. Among them, all-inorganic perovskites have attracted more attention than others in recent years because of their characteristics of large diffusion length, high luminescence efficiency, and good stability. In this work, Sb3+-doped RbCdCl3 crystalline powder was synthesized by a simple hydrothermal method, and its luminescence properties were studied, which showed a broad emission band with a large Stokes shift and efficient yellow light emission at about 596 nm at room temperature with a photoluminescence quantum yield of 91.7%. The emission came from the transition of the self-trapped exciton 1 (STE1) out of 3Pn (n = 0, 1, and 2) to S0 due to strong electron-phonon coupling, which scaled with increasing temperature. Moreover, its emission color became white at low temperatures due to the occurrence of transition of other self-trapped exciton 0 (STE0) state emission out of the 1S states of Sb ions to S0 in the lattice. These emission color changes may be used for temperature sensing, and this Sb3+-doped RbCdCl3 material expands the knowledge of the efficient luminescent inorganic material family for further applications of all-inorganic perovskites.

Efficient Yellow Self-Trapped Exciton Emission in Sb3+-Doped RbCdCl3 Metal Halides.

Lead-free lower-dimensional organic-inorganic metal halide materials have recently triggered intense research because of their excellent photophysical properties and chemical stability. Herein, we report a novel zero-dimensional (0D) organic-inorganic hybrid single crystal (TMA)2SbCl5·DMF (TMA = N(CH3)3, DMF= HCON(CH3)2), which exhibits typical self-trapped exciton (STE) emission with an efficient yellow emission at 630 nm and high photoluminescence quantum yield (PLQY) of 67.2%. The dual STE emission is attributed to the singlet and triplet STEs in inorganic [SbCl5]2-, respectively. Further, an ab initio molecular dynamics simulation was performed to estimate the stability of crystal structure at room temperature. The calculated excited-state structure indicates that the deformation parameter (Δd) of the excited-state structure is larger than that of the ground state, illustrating the origin of a large Stokes shift. These results indicate that these new 0D lead-free organic-inorganic hybrid metal halides are promising luminescent materials for optoelectronic applications.

Self-Trapped Exciton Emission in a Zero-Dimensional (TMA)2SbCl5·DMF Single Crystal and Molecular Dynamics Simulation of Structural Stability.

Environmentally friendly metal hybrid halides show great promise for white light emitting diode (WLED) applications due to their unique optical properties. Herein, a lead-free blue-light excited red-emitting Mn2+-based hybrid halide (CH6N3)2MnCl4 was obtained via a facile mechanochemical method. (CH6N3)2MnCl4 with octahedrally coordinated Mn2+ ions exhibits intense red emission at 650 nm with a high photoluminescence quantum yield (PLQY) of 55.9% benefiting from its unique crystal structure of ferromagnetic (FM) coupled trimeric [Mn3Cl12]6− linear chains. Besides, (CH6N3)2MnCl4 also possesses excellent thermal stability on account of the relatively weak electron–phonon coupling effect. Moreover, the luminescence intensity of (CH6N3)2MnCl4 can be significantly improved by 8% Zn2+ alloying. The WLEDs with different correlated color temperatures (CCT) fabricated using (CH6N3)2MnCl4:8%Zn2+ and the yellow phosphor Y3Al5O12:Ce3+ (YAG:Ce3+) using a blue LED chip exhibit much better overall electroluminescence performance than those based on (CH6N3)2MnCl4. A warm WLED with a CCT of 3984 K, a high luminous efficacy of 90.41 lm W−1 and a color rendering index (CRI) of 93.7 was obtained based on the modified (CH6N3)2MnCl4:8% Zn2+ halide, indicating its high potential as a red-emitting component for WLED applications.

Xinxin Han

Papers

Self-Trapped Exciton Emission in a Zero-Dimensional (TMA)2SbCl5·DMF Single Crystal and Molecular Dynamics Simulation of Structural Stability.

Lead-free MnII-based red-emitting hybrid halide (CH6N3)2MnCl4 toward high performance warm WLEDs