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Enhancement of Charge Transfer and Quenching of Photoluminescence of Capped CdS Quantum Dots.

Mehata MS - Sci Rep (2015)

Bottom Line: An external electric field of variable strength of 0.2-1.0 MV cm(-1) was applied to the sample of capped CdS Q-dots doped in a poly(methyl methacrylate) (PMMA) films.PL of capped CdS Q-dots is significantly quenched in presence of external electric field.Thus, understanding the CT character and field-induced PL quenching of CdS Q-dots is important for photovoltaic, LEDs and biological applications.

View Article: PubMed Central - PubMed

Affiliation: Laser-Spectroscopy Laboratory, Department of Applied Physics, Delhi Technological University, Bawana Road, Delhi 110042, INDIA.

ABSTRACT
Quantum dots (Q-dots) of cadmium sulfide (CdS) with three different capping ligands, 1-butanethiol (BT), 2-mercaptoethanol (ME) and benzyl mercaptan (BM) have been investigated. An external electric field of variable strength of 0.2-1.0 MV cm(-1) was applied to the sample of capped CdS Q-dots doped in a poly(methyl methacrylate) (PMMA) films. Field-induced changes in optical absorption of capped CdS Q-dots were observed in terms of purely the second-derivative of the absorption spectrum (the Stark shift), indicating an enhancement in electric dipole moment following transition to the first exciton state. The enhancement depends on the shape and size of the Q-dots prepared using different capping ligands. Field induced-change in photoluminescence (PL) reveals similar changes, an enhancement in charge-transfer (CT) character in exciton state. PL of capped CdS Q-dots is significantly quenched in presence of external electric field. The strong field-induced quenching occurs as a result of the increased charge separation resulting exciton dissociation. Thus, understanding the CT character and field-induced PL quenching of CdS Q-dots is important for photovoltaic, LEDs and biological applications.

No MeSH data available.


Related in: MedlinePlus

(a) Absorption spectrum with a Gaussian functions and the second derivative spectrum of G1 Gaussian function, (b) electroabsorption (E-A) spectra of BT-capped CdS Q-dots embedded in a PMMA film observed at two different angles of χ (=90° and 54.7°) at field strength of 0.7 MV cm−1 at 295 K. (c) E-A spectrum with the simulated spectrum.
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f1: (a) Absorption spectrum with a Gaussian functions and the second derivative spectrum of G1 Gaussian function, (b) electroabsorption (E-A) spectra of BT-capped CdS Q-dots embedded in a PMMA film observed at two different angles of χ (=90° and 54.7°) at field strength of 0.7 MV cm−1 at 295 K. (c) E-A spectrum with the simulated spectrum.

Mentions: Figures 1, 2, 3 show the electroabsorption (E-A) and absorption spectra of capped CdS Q-dots doped in a PMMA film. These spectra were recorded in a range of 15000–30000 cm−1 for BT capped and 16500–32500 cm−1 for ME and 17500–34000 cm−1 for BM capped CdS Q-dots. The average size of the Q-dots estimated from the absorption spectra is 3.8, 4.0 and 2.1 nm for BT, ME and BM capped CdS Q-dots, respectively. The absorption spectrum of BT and BM capped Q-dots was reproduced by using Gaussian functions, which are used in the simulation of the E-A spectra, except for ME capped Q-dots. In each case, the lowest energy absorption band is corresponding to the transitions to the first exciton state, which represents to the direct band gap of CdS Q-dots. The energy band gap of the capped CdS Q-dots varies with the particle size. A single absorption maximum is observed at 442 and 444 nm respectively for BT and ME capped Q-dots, whereas for BM capped Q-dots the absorption shows two band maxima at around two Gaussian functions (Fig. 3)7. The higher energy absorption band at 372 nm (G2) is assigned to the strongly quantized CdS clusters whereas the lower energy absorption band is at 427 nm (G1) might be corresponding to the aggregation. The first-derivative of the absorption spectrum or the Gaussian functions is also shown in Figs 1, 2, 3a. The absorption spectra of capped CdS Q-dots doped in a PMMA film are nearly the same as obtained in solution8.


Enhancement of Charge Transfer and Quenching of Photoluminescence of Capped CdS Quantum Dots.

Mehata MS - Sci Rep (2015)

(a) Absorption spectrum with a Gaussian functions and the second derivative spectrum of G1 Gaussian function, (b) electroabsorption (E-A) spectra of BT-capped CdS Q-dots embedded in a PMMA film observed at two different angles of χ (=90° and 54.7°) at field strength of 0.7 MV cm−1 at 295 K. (c) E-A spectrum with the simulated spectrum.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4499802&req=5

f1: (a) Absorption spectrum with a Gaussian functions and the second derivative spectrum of G1 Gaussian function, (b) electroabsorption (E-A) spectra of BT-capped CdS Q-dots embedded in a PMMA film observed at two different angles of χ (=90° and 54.7°) at field strength of 0.7 MV cm−1 at 295 K. (c) E-A spectrum with the simulated spectrum.
Mentions: Figures 1, 2, 3 show the electroabsorption (E-A) and absorption spectra of capped CdS Q-dots doped in a PMMA film. These spectra were recorded in a range of 15000–30000 cm−1 for BT capped and 16500–32500 cm−1 for ME and 17500–34000 cm−1 for BM capped CdS Q-dots. The average size of the Q-dots estimated from the absorption spectra is 3.8, 4.0 and 2.1 nm for BT, ME and BM capped CdS Q-dots, respectively. The absorption spectrum of BT and BM capped Q-dots was reproduced by using Gaussian functions, which are used in the simulation of the E-A spectra, except for ME capped Q-dots. In each case, the lowest energy absorption band is corresponding to the transitions to the first exciton state, which represents to the direct band gap of CdS Q-dots. The energy band gap of the capped CdS Q-dots varies with the particle size. A single absorption maximum is observed at 442 and 444 nm respectively for BT and ME capped Q-dots, whereas for BM capped Q-dots the absorption shows two band maxima at around two Gaussian functions (Fig. 3)7. The higher energy absorption band at 372 nm (G2) is assigned to the strongly quantized CdS clusters whereas the lower energy absorption band is at 427 nm (G1) might be corresponding to the aggregation. The first-derivative of the absorption spectrum or the Gaussian functions is also shown in Figs 1, 2, 3a. The absorption spectra of capped CdS Q-dots doped in a PMMA film are nearly the same as obtained in solution8.

Bottom Line: An external electric field of variable strength of 0.2-1.0 MV cm(-1) was applied to the sample of capped CdS Q-dots doped in a poly(methyl methacrylate) (PMMA) films.PL of capped CdS Q-dots is significantly quenched in presence of external electric field.Thus, understanding the CT character and field-induced PL quenching of CdS Q-dots is important for photovoltaic, LEDs and biological applications.

View Article: PubMed Central - PubMed

Affiliation: Laser-Spectroscopy Laboratory, Department of Applied Physics, Delhi Technological University, Bawana Road, Delhi 110042, INDIA.

ABSTRACT
Quantum dots (Q-dots) of cadmium sulfide (CdS) with three different capping ligands, 1-butanethiol (BT), 2-mercaptoethanol (ME) and benzyl mercaptan (BM) have been investigated. An external electric field of variable strength of 0.2-1.0 MV cm(-1) was applied to the sample of capped CdS Q-dots doped in a poly(methyl methacrylate) (PMMA) films. Field-induced changes in optical absorption of capped CdS Q-dots were observed in terms of purely the second-derivative of the absorption spectrum (the Stark shift), indicating an enhancement in electric dipole moment following transition to the first exciton state. The enhancement depends on the shape and size of the Q-dots prepared using different capping ligands. Field induced-change in photoluminescence (PL) reveals similar changes, an enhancement in charge-transfer (CT) character in exciton state. PL of capped CdS Q-dots is significantly quenched in presence of external electric field. The strong field-induced quenching occurs as a result of the increased charge separation resulting exciton dissociation. Thus, understanding the CT character and field-induced PL quenching of CdS Q-dots is important for photovoltaic, LEDs and biological applications.

No MeSH data available.


Related in: MedlinePlus