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Dos Santos CHD, Ferreira DL, Zucolotto Cocca LH, Mourão RS, Schiavon MA, Mendonça CR, De Boni L, Vivas MG. Size-dependent photoinduced transparency in colloidal CdTe quantum dots in the strong confinement regime: an inverse linear relationship. Phys Chem Chem Phys 2022; 25:359-365. [PMID: 36477139 DOI: 10.1039/d2cp05006d] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022]
Abstract
Nanomaterials have been investigated as saturable absorbers for ultrafast lasers because of their large photoinduced transparency related to ground-state bleaching. However, the quantum dot size effect on the photoinduced transparency in the strong confinement regime has not been explored due to the challenge of accurately measuring the ground state and the excited-state absorption cross-sections. At the same time, these optical properties are essential to calculate several chemical and physical quantities at the nanoscale. In this context, we have employed the photoluminescence saturation method to determine the ground-state absorption cross-section and the femtosecond open-aperture Z-scan technique to investigate the size-dependent ground-state bleaching of glutathione-capped CdTe QDs synthesized in an aqueous medium. The results were modeled using rate equations within the three-energy levels approach. Our results pointed out that the photoinduced transparency rate at the 1S3/2(h) → 1S(e) transition peak presents an inverse linear relationship with the QD diameter (from 2.2 nm up to 3 nm). Otherwise, the larger QDs have a higher ground-state cross-section, which is directly proportional to the ground-state bleaching. To explain this apparent contradiction, we calculate the effective absorption coefficient αeff = σ/V (σ is the absorption cross section and V is the QD volume) for the QDs and observed that the smaller QDs have a higher absorption from the ground to the first excited state, corroborating our results. Finally, our results showed that the saturable absorption effect in CdTe-QDs is slightly higher than that obtained for graphene and other 2D materials and smaller than the black phosphorus in the visible region.
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Affiliation(s)
- Carlos H D Dos Santos
- Laboratório de Espectroscopia Óptica e Fotônica, Universidade Federal de Alfenas, Poços de Caldas, MG, Brazil. .,Instituto de Física de São Carlos, Universidade de São Paulo, Caixa Postal 369, 13560-970 São Carlos, SP, Brazil.
| | - Diego L Ferreira
- Laboratório de Espectroscopia Óptica e Fotônica, Universidade Federal de Alfenas, Poços de Caldas, MG, Brazil.
| | - Leandro H Zucolotto Cocca
- Instituto de Física de São Carlos, Universidade de São Paulo, Caixa Postal 369, 13560-970 São Carlos, SP, Brazil.
| | - Rafael S Mourão
- Grupo de Pesquisa em Química de Materiais, Universidade Federal de São João del-Rei, São João del-Rei, MG, Brazil
| | - Marco A Schiavon
- Grupo de Pesquisa em Química de Materiais, Universidade Federal de São João del-Rei, São João del-Rei, MG, Brazil
| | - Cleber R Mendonça
- Instituto de Física de São Carlos, Universidade de São Paulo, Caixa Postal 369, 13560-970 São Carlos, SP, Brazil.
| | - Leonardo De Boni
- Instituto de Física de São Carlos, Universidade de São Paulo, Caixa Postal 369, 13560-970 São Carlos, SP, Brazil.
| | - Marcelo G Vivas
- Laboratório de Espectroscopia Óptica e Fotônica, Universidade Federal de Alfenas, Poços de Caldas, MG, Brazil.
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