紫外凝胶中掺杂的PbSe量子点的近红外吸收发射截面
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Near-infrared absorption–emission cross-sections of PbSe quantum
dots doped in UV gel
$
Cheng Cheng
a,
n
, Yinhui Xu
a
, Xiaoyu Cheng
b
a
Department of Applied Physics, Zhejiang University of Technology, Hangzhou 310023, China
b
School of Chemistry, University of New South Wales, Sydney, NSW 2033, Australia
article info
Article history:
Received 23 December 2014
Received in revised form
2 February 2015
Accepted 17 February 2015
Available online 20 February 2015
Keywords:
PbSe quantum dot
Absorption cross-section
Emission cross-section
Doping concentration
Wavelength dependence
abstract
We measure near-infrared absorption spectra of PbSe quantum dots (QDs) with three sizes (4.5, 5.0, and
5.6 nm) doped in UV gel with the concentration of 0.25–1.50 mg mL
1
by using an absorption-spectrum
method. An empirical formula is proposed to describe the correlation of the first–second absorption-
peak wavelengths and QD size. The peak-absorption cross-section is measured as 2.76–3.69 10
16
cm
2
for 5.6-nm QD, and the absorption coefficient ranges in 0.19–0.59 cm
1
, both associated with the doping
concentration and the QD size. Furthermore, the emission cross-sections are determined by measuring
the photoluminescence spectra of QDs and using the McCumber relationship, which depend weakly on
both the doping concentration and the QD size. For 5.6-nm QD, the measured peak-emission cross-
section is 3.36–4.48 10
16
cm
2
within the range of experimental doping concentration.
& 2015 Elsevier B.V. All rights reserved.
1. Introduction
Nanocrystal quantum dots (QDs) have drawn considerable re-
search interests in recent years [1]. A series of special optical
features are observed in QDs due to the confinement of charge
carriers within the physical dimension defined by particle size. IV–
VI QDs, such as PbSe, PbS, PbTe etc. emit in the near infrared re-
gion as favored in a number of applications. Among them, PbSe
QDs with relatively simple electronic structural and high quantum
yield have attracted much attention in recent years [2].
Absorption–emission cross-sections are important photo-phy-
sical parameters of QDs. For CdSe QDs, the cross sections were
measured by the absorption-spectrum method (e.g., [3]). For PbSe
QDs, Du et al. [4] measured the absorption and emission spectra of
PbSe QD within the range of 1000 –1850 nm, and determined the
absorption-peak wavelength in 1120–1880 nm for PbSe QD with
3–8 nm diameter. The emission-peak wavelength was in 1210–
1450 nm for PbSe QD of 3–4.5 nm, and the photoluminescence
(PL) lifetime was 300 ns. Using the absorption-spectrum method,
Brumer et al. [5] measured the cross-sections of PbSe (core), PbSe/
PbS (core/shell), PbSe/PbSe
x
S
1 x
(core/shell), which were prepared
by organic thermal synthesis. The absorption–emission-peak
cross-sections of PbSe QD with 5.4-nm diameter were determined
as 1.25 10
16
cm
2
and 0.55 10
16
cm
2
, respectively. Cheng
et al. [6] measured the absorption and emission spectra of PbSe QD
dispersed in n-hexane, and obtained absorption-peak cross-sec-
tion of 3.54 10
16
cm
2
.
In the above work, the reported cross-sections were either only
for single size of QD, or only for monodisperse QD, where the
doping concentrations were not given, i.e., effect of doping con-
centration was not considered. This gave an incomplete model as
doping concentration inevitably affects the cross sections due to
surface effect and fluorescence quenching. In particular, the sur-
face effect arises from difference in dielectric-constant between
QD and the media, enhancing the resonance capturing and redu-
cing defect states, which in turnleads to varied cross-sections
throughout the media. Therefore, it is considerable to study the
cross-sections of QDs with different diameters and doping con-
centrations in the given media, which has been seldom reported.
Recent studies showed that ultraviolet (UV) gel was an ideal
background material for QDs doped fiber laser due to its good
transparency in the near infrared region, low reduction of volume
during drying and desirable refraction index (n¼ 1.464) that is
slightly higher than the SiO
2
fiber claddings [7]. QD doped fibers
with designed concentration can be obtained if colloidal PbSe QDs
are mixed into UV gel and injected into hollow optical fibers to
configure the gain fiber, even to constitute QD doped fiber am-
plifiers and lasers [6,7]. Therefore, we focus on the UV–gel matrix
in this paper.
We measured the absorption spectra of PbSe QDs with three
sizes which were doped in UV gel, proposing an empirical formula
Contents lists available at ScienceDirect
journal homepage: www.elsevier.com/locate/optcom
Optics Communications
http://dx.doi.org/10.1016/j.optcom.2015.02.034
0030-4018/& 2015 Elsevier B.V. All rights reserved.
☆
This work is supported by the National Natural Science Foundation of China
under Grant 61274124 and Grant 61474100.
n
Corresponding author.
E-mail address: chengch@zjut.edu.cn (C. Cheng).
Optics Communications 347 (2015) 108–112
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