Real Time Spectroscopic Monitoring of the Synthesis of
Core/Shell 𝛽-NaYF4 Nanocrystals
Lance Kotter, Md Yeathad Hossan, P. Stanley May
Department of Chemistry, University of South Dakota, Vermillion, SD 57069
The inert shell was added to core NaYF4:17% Yb, 3% Er UCNP in order to
increase the green luminescence of the nanocrystals by reducing surface
quenching. Surface quenching is the quenching of excited lanthanide ions by
surface defects, ligands, or solvents.
Real-time luminescence monitoring (RTM) data
Inert Shell Addition to NaYF4:17% Yb,
3% Er
Core Synthesis NaYF4:17% Yb, 3% Er
70
Figure 9. A.) image of
the synthesis of core
NaYF4:17% Yb, 3% Er.
B.) Image after the
addition of inert shell
NaYF4 to core. Both
images were taken at
300 ℃.
200
60
180
Upconversion Intensity
Upconversion Intensity
Upconversion nanocrystals (UCNC’s) are unique in that the emission
wavelength is shorter, (higher energy) than that of the excitation
wavelength. Lanthanide-doped NaYF4 nanocrystals are the most
efficient upconverters and have various applications such as security
printing. Real-time spectroscopic monitoring of luminescence is
applied to study the reaction mechanism of the synthesis of core 𝛽NaYF4:17% Yb, 3% Er nanocrystals and also the shell addition to that
core.
A.)
B.)
Discussion
Results
Introduction
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Reaction Time / mins
350
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15
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Figure 5. active shell
NaYF4:10% Yb, 10% Nd
addition to core NaYF4:17% Yb,
3% Er. The red represents the
temperature of the reaction and
the blue represents the
upconversion intensity using
808 nm excitation.
Reaction time / mins
SEM Image
TEM Images
Figure 6. Core
NaYF4:17% Yb, 3% Er.
Figure 7. Inert shell
NaYF4 addition to core
NaYF4:17% Yb, 3% Er.
Approx. 4 nm
43 nm
Figure 8. Active shell
NaYF4:10% Yb, 10%
Nd addition to core
NaYF4:17% Yb, 3% Er.
4I
13/2
4I
9/2
2F
Nd3+
4I
15/2
7/2
Yb3+
Er3+
12
nm
Core / inert shell dimensions.
Light blue= core; dark blue= shell
Acknowledgements
This work was made possible by the National Science Foundation REU Security Printing
and anti-counterfeiting site EEC-1560323. A Special thanks to Dr. May at USD for being a
great mentor. Md Yeathad Hossan for allowing me to work with him on this project. I
would also like to thank everyone in the SPACT program and the chemistry department at
USD.
References
Approx. 3 nm
43 nm
26 nm
Figure 2.
Real-time
spectroscopic
monitoring
set-up.
Figure 10. Energy level
diagram showing the energy
transfer from Nd3+ ion to Yb3+
ion to the Er3+ ion.
4I
11/2
5/2
Through the addition of an active shell NaYF4:10% Yb, 10% Nd, the
nanocrystals were excited with 808 nm light. This was the first time an active
Nd3+ doped shell was used and it produced encouraging results.
26 nm
For the core/active
shell the solution is
excited by 808 nm
light as the Nd3+ is
the sensitizer ion.
3/2
It has been shown through real-time luminescence monitoring that the inert
shell addition to the core increases the luminescent properties up to ten times
that of the core through reduced surface quenching.
Real time monitoring set-up
For the core, core/inert shell the solution is excited by 980 nm light as
the Yb3+ ion is the sensitizer ion.
5/2
Conclusions
Shell addition
• Sacrificial 𝛼-NaYF4 or 𝛼-NaYF4:10% Yb, 10% Nd nanoparticles
(4-8 nm) are added to the core 𝛽-NaYF4:17% Yb, 3% Er
nanoparticles in solution.
• The solution is then heated to 300℃ and monitored by real-time
spectroscopy. Sacrificial nanoparticles deposit on core
nanoparticles, forming an active (10%Yb, 10% Nd) or inert (100%
Y) shell.
4F
2F
40
50
The active shell NaYF4:10% Yb, 10% Nd was a success because energy
transfer was observed from the sensitizer ion Nd3+ to the Yb3+ ion to the visible
activator Er3+ ion. This shell addition was excited with 808 nm light and
monitored in the visible spectrum. There is clear evidence that the
upconversion luminescence increased during the reaction.
4F
35
Y, Yb, and Er acetates are dissolved in oleic acid / octadecene.
Solution is heated to 110 ℃ to convert acetates to oleates.
NaOH and NH4F is then added.
Temperature increased to 300 ℃ and reaction monitored by realtime spectroscopy.
60
45
300
Temperature / ℃
•
•
•
•
50
Active Shell addition to core NaYF4:17% Yb,
3% Er
upconversion nanocrystals. A.) Sample in ambient light. B.) sample under 980
nm excitation. (Jeevan et al., 2012)
Procedures
Core Synthesis
40
Figure 4. RTM of inert shell NaYF4
addition to core NaYF4:17% Yb, 3% Er.
Upconversion Intensity
Figure 1. QR code printed using security ink based on NaYF4:17% Yb, 3% Er
30
Reaction Time / mins
Figure 3. RTM of synthesis of core
NaYF4:17% Yb, 3% Er.
B.)
A.)
6
nm
Core / active shell dimensions.
Light blue= core; dark blue= shell
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printing of covert quick response codes using upconverting nanoparticle inks. Nanotechnology,
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Suter, J. D., Pekas, N. J., Berry, M. T., & May, P. S. (2014). Real-Time-Monitoring of the Synthesis of
β-NaYF4:17% Yb,3% Er Nanocrystals Using NIR-to-Visible Upconversion Luminescence. The
Journal of Physical Chemistry C, 118(24), 13238-13247. doi: 10.1021/jp502971j
May, P. B., Suter, J. D., May, P. S., & Berry, M. T. (2016). The Dynamics of Nanoparticle Growth and
Phase Change During Synthesis of β-NaYF4. The Journal of Physical Chemistry C, 120(17), 94829489. doi: 10.1021/acs.jpcc.6b01365