Mechanical on–off photoluminescence in hybrid metal halides - Dr. Yonggang Wang

DECEMBER 25, 2021

Stimulus-responsive photoluminescent materials have attracted extensive research attention in recent years owing to their potential application in information storage and switch devices. Most of the materials that exhibit such phenomena are small organics, organometallic materials, liquid crystals, or polymer networks. At present, materials with high pressure sensitivity and high contrast are still in short supply. Recently, new work from a research team co-led by Prof. Jing Zhao from University of Science and Technology Beijing (USTB) and Dr. Yonggang Wang from HPSTAR reported their discovery of hybrid metal halides exhibiting stimulus-responsive photoluminescence (PL) phenomenon. Their results were published online recently in Adv. Funct. Mater.

Organic-inorganic hybrid metal halides which are star materials in the photoelectric area for their applications in PL, solar cells, lasers, X-ray detectors, and light-emitting diodes. Some researchers have studied the effects in organic-inorganic hybrid metal halides by applying high-pressure, which can tailor their structure and band gap, and some compounds shown interesting pressure-induced emission owing to phase transition. Only countable PL 'on' and 'off' responsive materials have been reported, which were almost organic compounds.

The research team synthesized two new organic-inorganic hybrid metal halides (Bmpip)9Pb3Zn2Br19 and (Bmpip)9Pb3Cd2Br19, which exhibit reversible “PL-on” and “PL-off” states under grinding and pressure. Notably, the as-obtained compounds were non-emissive under UV light at ambient conditions but exhibited bright PL upon grinding or under hydrostatic pressure. Interestingly, the PL is quenchable by short-time annealing or storage in air for one week, and the process is repeatable. Moreover, pressure-induced PL and PL-enhancement phenomena were observed in both compounds, which were similar to but slightly different than the above-mentioned mechano-PL.

Comprehensive techniques were used to reveal the mechanism of the “on-off” phenomenon. Through a combination of structural and spectral analyses, the crucial role of the organic cations interacting with inorganic chromophores in the “on-off” PL behavior of the title compounds was revealed. To explore the possible applications of the compounds in handwriting tracking, damage detection, and stress recording, a composite film was prepared, which exhibiting excellent effection in certain scenes. 

“Our findings will have important implications to understand the stimulus-responsive PL mechanism and provide a good foundation for future practical applications,” said Dr. Wang.

Caption: (a) Compound 1 under daylight and 365 nm UV light. PL and PL excitation spectra of the single crystal (SC), fresh powder (fresh), PL quenched powder (Que.), and repeated powder (Rep.) of 1 (b) and 2 (c). PL decay lifetime of the fresh powder and repeated powder of 1 (d) and 2 (e) at RT.

近年来，刺激响应型有机光致发光材料在信息存储和开关器件等诸多领域展现出广泛的应用潜力。然而，此类材料中具有高的压力响应灵敏度和高发光对比度的比较稀缺。最近，北科大赵静课题组和北京高压科学研究中心王永刚课题组合作的最新研究发现了两种新的有机无机杂化材料具有优异的机械力响应发光性质。这两种本身不发光的化合物在研磨或静水压力下表现出明亮的紫外光致绿光发射，且能通过退火或放置实现可逆的发光和不发光现象。进一步的结构研究表明该类材料的研磨荧光“开-关”和高压荧光变化行为主要归因于有机阳离子的重新排布和无机八面体的变形。相关研究成果以“Reversible Mechanically Induced On-Off Photoluminescence in Hybrid Metal Halides”为题发表在《先进功能材料》上。