A research group led by Professor WU Kaifeng of the Dalian Institute of Chemical Physics (DICP) of the Chinese University of Science (CAS), in collaboration with Dr Peter C. Sercel of the Center for Hybrid Organic Inorganic Semiconductors for Energy recently reported the use of lattice distortion in lead halide perovskite quantum dots (QDs) to control their precise exciton structure.
The study was published in Biological Sciences on September 1. 8.
It is well known that the crystal shape or anisotropy in QDs, which are small semiconductor nanoparticles, results in the splitting energy of their bright excitons (electron-hole pair bonds), which is called the fine splitting structure. . (FSS). These excitons provide an important playground for quantum information science. For example, the FSS of excitons can be used for edge control of quantum states for quantum computers, or for photon pairs combining polarization in quantum optics, although the latter is necessary to limit the separation.
Traditionally, studying FSS usually requires one or a few QDs at the temperature of liquid helium, due to its influence on the size and shape of the QDs. Measuring FSS at a fixed level, let alone controlling it, seems impossible if all the points are nearly identical.
In this study, using ensemble-level femtosecond polarized absorption transients, the researchers observed clear exciton fluorescence FSS in treated CsPbI3 perovskite QDs, which manifested as quantum exciton beats ( time oscillations of kinetic traces).
“Even more surprisingly, the frequency of beating, as determined by the FSS power, of a given sample can be continuously controlled by changing the temperature. This is an unprecedented result, which means that scientists can now control the FSS through heat,” said the WU professor.
The researchers also found that temperature-dependent FSS is associated with an interesting and highly sensitive network of lead halide perovskites. Lowering the temperature led to an octahedral lead-iodide layer again.
Calculations showed that because these orthorhombic-phase QDs are actually members of the pseudocubic family whose crystal planes are still limited, the lattice distortion takes place first and avoids crossing the positive space between the bright spots. This difference is for the observed FSS, it can be detected despite the differences in the size of the QD and its shape in the aggregate form.
“Lattice distortion in CsPbI3 perovskites is well known in the photovoltaic community, as it relates to the question of the stability of perovskite solar cells, but no one has previously linked it experimentally to the true structure of the ‘exciton,’ Professor WU said.. “Our study shows that this property can actually be used to control the separation of bright excitons in quantum dots for quantum information technology.”
