APPLIED PHYSICS LETTERS 100, 013109 (2012)
Marius Hossu, Zhongxin Liu, Mingzhen Yao, Lun Ma, and Wei Chena)
Department of Physics, The University of Texas at Arlington, Arlington, Texas 76019-0059, USA
(Received 3 November 2011; accepted 12 December 2011; published online 5 January 2012)
CdTe quantum dots have intense photoluminescence but exhibit almost no x-ray luminescence.
However, intense x-ray luminescence from CdTe quantum dots is observed in LaF3:Ce/CdTe
nanocomposites. This enhancement in the x-ray luminescence of CdTe quantum dots is attributed to
the energy transfer from LaF3:Ce to CdTe quantum dots in the nanocomposites. The combination of
LaF3:Ce nanoparticles and CdTe quantum dots makes LaF3:Ce/CdTe nanocomposites promising
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scintillators for radiation detection. 2012 American Institute of Physics. [doi:10.1063/1.3674313]
For radiation detection, the sensitivity, response time, and
energy resolution are important.1,2 To meet these require-
ments, a scintillator must have a high luminescence quantum
efficiency, a short luminescence lifetime, high stopping power,
as well as high carrier mobility-lifetime products.2 Ce3þ is a
great activator exhibiting a very fast response in radiation
detectors of medical imaging systems employed in diagnostic
radiology.3–6 Currently, Ce3þ doped scintillators meet most of
the requirements and have become popular scintillators for
radiation detection and dosimetry.3–6 However, Ce3þ doped
scintillators have their own shortcomings. For example, some
Ce3þ doped scintillators such as LaBr3:Ce3þ have very high
quantum efficiency and energy resolution, but they are hygro-
scopic, making them impractical for many applications. In
addition, most Ce3þ doped scintillators have emission in the
ultraviolet (UV) range. For practical applications, this is
potentially an issue. For example, when the nanoparticles are
embedded into polymers for radiation detection, the sensitivity
might be reduced because the UV emission cannot penetrate
most polymers. Quantum dots such as CdTe and CdSe can
have very high quantum efficiencies as a consequence of
quantum size confinement,7–9 up to 98% (Ref. 10) and short
luminescence lifetimes in the nanosecond range.11–13 There-
fore, in principle, semiconductor quantum dots could be prom-
ising for radiation detection because of their short lifetimes
and high sensitivities. However, the stopping power of most
II-VI quantum dots is low and their scintillation luminescence
is very weak.14 The combination of high stopping power and
sensitivity of LaF3:Ce nanoparticles with the high emitting
rate as well as the emission tenability of CdTe quantum dots
may overcome the shortcomings of Ce3þ doped scintillators
and semiconductor quantum dots; therefore, they can provide
improved properties for radiation detection. The possible
energy transfer from Ce3þ doped scintillation nanoparticles to
semiconductor quantum dots is the key for the design of these
new materials and the energy transfer rate could be very high
because the absorption maximum of the quantum dots can be
tuned by size to have a large overlap with the emission peak
of LaF3:Ce nanoparticles. These energy transfer based nano-
composites may be promising for radiation detection. In this
communication, we report the observation of x-ray lumines-
cence from CdTe quantum dots in LaF3:Ce/CdTe nanocompo-
sites and investigate their potential application as a new kind
of scintillators for radiation detection.
CdTe/LaF3:Ce nanocomposites were prepared by a wet-
chemistry method in two steps. In the first step, CdTe quan-
tum dots coated with thioglycolic acid (TGA) surfactant
were synthesized. In the second step, LaF3:Ce nanoparticles
were attached to CdTe quantum dots to form LaF3:Ce/CdTe
nanocomposites. To synthesize CdTe quantum dots, Cd2þ
-
containing solution was prepared by dissolving 0.7311 g of
Cd(ClO4)2ꢀH2O in 125 ml of water. Then, TGA (0.396 mole)
was added to the solution, and the pH value was adjusted to
ꢁ11 by the addition of 0.1 M NaOH. The solution was then
purged with nitrogen for at least 30 min. H2Te gas was gen-
erated by the chemical reaction of excess aluminum telluride
with 0.5 M sulfuric acid in an inert atmosphere (nitrogen)
and was combined with the above solution containing Cd2þ
ions using the setup as described.15 After the completion of
the reaction a yellow solution of CdTe nanocrystal nuclei
was obtained. This solution was then refluxed at 100 ꢂC to
promote crystal growth with the particle size controlled by
the reaction time.
To form LaF3:Ce/CdTe nanocomposites, 6.3 mmol of
La(NO3)3 and 0.7 mmol of Ce(NO3)3ꢀ6H2O were first dis-
solved in 15 ml of deionized water and then mixed with
10 ml of the CdTe nanoparticle solution prepared in step-1.
1 ml diethylene glycol (DEG) was added to the mixture solu-
tion as a surfactant. Ce(NO3)3 was used at a concentration of
0.1 M to provide the Ce3þ dopant. The chemicals were
mixed thoroughly, and then 20.1 mmol of NH4F water solu-
tion with a volume of 5 ml added drop wise to the mixture
solution under stirring at room temperature. The reaction so-
lution was stirred at room temperature for 0.5 h and subse-
quently was heated to 50 ꢂC for different reaction times up to
3.5 h under protection of nitrogen. The product was centri-
fuged, washed with de-ionized water three times, and dried
at 40 ꢂC in a vacuum atmosphere.
The identity, crystalline structure, size, and shape of the
nanoparticles were observed by high-resolution transmission
electron microscopy (HRTEM). The HRTEM images of the
particles were obtained with a JEOL JEM-2100 electron
microscope with accelerating voltage of 200 kV. X-ray lumi-
nescence was measured in a light-proof x-ray cabinet
equipped with optic fiber connection to an outside detector.
X-ray irradiation (60 kV and 5 mA) was performed using a
Faxitron RX-650 X-ray cabinet (Faxitron X-Ray Corp., IL,
a)Author to whom correspondence should be addressed. Electronic mail:
weichen@uta.edu. Telephone: 817-272-1064. Fax: 817-272-3637.
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0003-6951/2012/100(1)/013109/3/$30.00
100, 013109-1
2012 American Institute of Physics
132.203.227.61 On: Tue, 15 Jul 2014 19:30:27
Hossu, Marius
