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Defect-Mediated CdS Nanobelt Photoluminescence Up-Conversion

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journal contribution
posted on 12.07.2017, 00:00 by Yurii V. Morozov, Sergiu Draguta, Shubin Zhang, Alejandro Cadranel, Yuanxing Wang, Boldizsar Janko, Masaru Kuno
Laser cooling in semiconductors has recently been demonstrated in cadmium sulfide nanobelts (NBs) as well as in organic–inorganic lead halide perovskites. Cooling by as much as 40 K has been shown in CdS nanobelts and by as much as 58 K in hybrid perovskite films. This suggests that further progress in semiconductor-based optical refrigeration can ultimately lead to solid state cryocoolers capable of achieving sub 10 K temperatures. In CdS, highly efficient photoluminescence (PL) up-conversion has been attributed to efficient exciton–longitudinal optical (LO) phonon coupling. However, the nature of its efficient anti-Stokes emission has not been established. Consequently, developing a detailed understanding about the mechanism leading to efficient PL up-conversion in CdS NBs is essential to furthering the nascent field of semiconductor laser cooling. In this study, we describe a detailed investigation of anti-Stokes photoluminescence (ASPL) in CdS nanobelts. Temperature- and frequency-dependent band edge emission and ASPL spectroscopies conducted on individual belts as well as ensembles suggest that CdS ASPL is defect-mediated via the involvement of donor–acceptor states.