Pressure induced phase transitions of bulk CsGeCl and ultrafast laser pulse induced excited-state properties of CsGeCl quantum dots.

First-principles calculations are carried out to investigate the structural, electronic, and optical properties of CsGeCl. The results indicate that CsGeCl undergoes three structural phase transitions from or 3 to 3̄ at 8.5 GPa, from 3̄ to ppPv- at 9.4 GPa, and from ppPv- to 4 at 64 GPa, respectively. Meanwhile, the relation between the band gap and pressure implies that the band gap value of ppPv- is 1.56 eV at 40 GPa, making it a potential photovoltaic material. Based on pressure-induced stable structures, the CsGeCl quantum dots (QDs) have been fabricated to investigate the excited-state properties by tuning ultrafast laser pulses based on time-dependent density functional theory (TDDFT). The excited-state properties show that CsGeCl QDs have a wider absorption range compared with their bulk materials and their optical responses can be regulated by changing the laser intensity and wavelength. Our results further reveal that the 3-QDs exhibit excellent optical performance and have potential applications in optoelectronic devices.