Transcript SPECTROSCOPIC INVESTIGATION OF THE UP

THE SPECTROSCOPIC INVESTIGATION OF THE
UP-CONVERSION NANOPARTICLES FOR
BIOMEDICAL APPLICATIONS
D.V. Pominova, A.V. Ryabova, S.V. Kuznetsov, A.A. Luginina
Laser Biospectroscopy Lab.,
A.M. Prokhorov General Physics Institute,
Russian Academy of Sciences,
Moscow, Russia
E-mail: [email protected] Web: www.nsc.gpi.ru/lbs.html, www.biospec.ru
Introduction
The problem of screening and application of luminescent agents currently remains
one of the most vital in biology and medicine. There is great interest in the study of
diagnostic and therapeutic properties of the phosphors as which can be used different
nanoscale structures and particles. Some nanomaterials such as gold nanoparticles,
quantum dots and polymers are already widely used. However, growing interest to the
so-called up-conversion nanoparticles, which can absorb some NIR photons and then
can emit luminescence in the visible region of the spectrum.
Compared with organic phosphors and semiconductor nanocrystals, nanoparticles,
with the possibility of the up-conversion mechanism luminescence excitation (up-NP)
have a number of advantages, namely: providing a high photochemical stability,
narrow emission band and large distances (up to 500 nm) between the individual
luminescence peaks and excitation wavelength in the infrared range that allows them
to be easily separated. Along with the increased penetration depth of light and lack of
stray fluorescence from biomolecules under IR - excitation, such up-NP are perfect for
use as fluorescent probes in biological studies and for fluorescence diagnostic. Also,
the photobleaching and phototoxicity are reduced under IR irradiation.
Purpose of investigation:
• to research spectral-luminescence and upconversion properties of nanoparticles with the host
SrF2 doped with rare earth ions Yb3+- Er3+, Yb3+- Er3+Tm3+, depending on the concentration and doping
composition.
Sample
F490
F517
F519
F521
F530
F588
Composition
SrF2:15%YbF3/2%ErF3
SrF2:15%YbF3/3%ErF3
SrF2:15%YbF3/5%ErF3
SrF2:15%YbF3/7,5%ErF3
SrF2:10%YbF3/1%ErF3
SrF2:10%YbF3/1%ErF3/0.5%TmF3
Concentration
Composition
Equipment
• For the synthesis was used co-precipitation from water
solutions method.
• Hydrodynamic sizes of nanoparticles in liquids were
estimated by multi-angle spectrometer of dynamic light
scattering Photocor Complex (Russia).
• Fluorescent studies were performed using the laserinduced fluorescence spectroscopy, including the optical
fiber spectrum analyzer LESA-01-Biospec, modified with
integrating sphere Avantes, laser 974 nm.
• Kinetic characteristics of up-conversion luminescence in
blue, green and red range were prepared using non
descanned regime on microscope Carl Zeiss LSM-710-NLO
with femtosecond laser excitation.
The experimental setup for up-conversion
efficiency measurements
QY 
 P
P
i 1, 2, 3
Sample
i
i _ emitted
Sample
974 _ absorbed

i 1, 2,3

i
Re ference
P
974 _ scattered
Sample
P
P
i _ emitted
Sample
974 _ scattered
PSample974_absorbed – absorbed by the sample
exiting laser power;
Psamplei_emitted – emitted up-conversion
light (power integrated over the
380-780 nm or 420-870 nm ranges,
depending on the used dopants);
PReference974_scattered – scattered by the
undoped sample power, which emulates
the sample scattering;
PSample974_scattered – the power scattered by
doped sample.
Typical luminescence spectra of Yb3+ , Er3+ doped phosphors at
room temperature under IR excitation and simplified energy
level diagram of Er3+ and Yb3+
GSA – ground state absorbtion;
ESA – exited state absorbtion;
ETU – energy transfer up-conversion
BET – back energy transfer
Up-conversion luminescence spectra for
selected samples under 974 nm excitation
2000
Sample
15%YbF3 2%ErF3
1800
1600
15%YbF3 3%ErF3
1400
15%YbF3 5%ErF3
1200
I, a. u. 1000
15%YbF3 7.5%ErF3
800
600
400
200
0
450
500
550 λ, nm
600
650
700
750
4000
10%YbF3 1%ErF3
3500
10%YbF3 0.5%ErF3 0.5%TmF3
3000
2500
I, a. u. 2000
1500
1000
500
0
450
500
550
λ, nm
600
650
700
750
SrF2 15%YbF3
2%ErF3
SrF2 15%YbF3
3%ErF3
SrF2 15%YbF3
5%ErF3
SrF2 15%YbF3
7.5%ErF3
SrF2 10%YbF3
1%ErF3
SrF2 10%YbF3
0.5%ErF3 0.5%TmF3
NP
radius, QY, %
nm
20
0.10
20
0.11
50
0.05
40
0.03
10
0.42
15
0.03
Kinetic characteristics of up-conversion luminescence
In this paper was proposed and tested a new
method for visualizing and studying the kinetics of
up-conversion luminescence. Luminescence lifetime
measurement was performed using a confocal
microscope Carl Zeiss LSM 710 NLO. The
luminescence was excited by a femtosecond pulsed
tunable laser Chameleon Coherent (780-1080 nm)
with a wavelength 974 nm. The measurements
were prepared using non descanned regime. Laser
scanned over the sample surface at a rate of about
1.3 microseconds per pixel. Detector fixed
luminescence intensity corresponding to each pixel
of the scan.
Since the decay time of the samples is much
larger than the scanning speed of one pixel, it were
obtained glowing strips, the so-called fluorescent
tracks .
With further software processing and
approximation were obtained the times of the
luminescence decay.
The experimental values ​of the up-conversion
luminescence decay time
t

I(t) А  1 - е  r


  t
е d
 
 
  t
I(t ) А   е dec


Sample








Composition
F490 SrF2:15%YbF3/2%ErF3
F517 SrF2:15%YbF3/3%ErF3
F519 SrF2:15%YbF3/5%ErF3
F521 SrF2:15%YbF3/7,5%ErF3
F530 SrF2:10%YbF3/1%ErF3
F588 SrF2:10%YbF3/1%ErF3/0.5%TmF3
The Er3+ (4S3/2,2H11/2) → 4I15/2 transition has
an instantaneous rise during the excitation pulse
in addition to a delayed rise after the end of the
excitation pulse, showing that both excited state
absorption (ESA) and energy-transfer upconversion (ETU) processes are involved in the
Er3+ (4S3/2,2H11/2) green level population.
The lifetimes associated with the green light
emitting level become shorter with increasing
Lifetime, concentration of dopant ions.This confirms the
predominance of back energy transfer in the
mks
depopulation mechanism of the up-conversion
15±2
emitting levels.
15±2
With increasing concentration of dopant
10±2
ions, the distance between donor and acceptor is
5±2
decreased and at high concentrations begins the
concentration quenching.
25±2
10±2
Results
•
•
•
During the energy transfer from donor to acceptor the population of the level 4S3/2 is
increases from which green emission occurs and thus the intensity of the luminescence
of the acceptor increases . However, apart from the direct transfer of energy, there is a
possibility of reverse energy transfer from donor to acceptor, at which the state 4S3/2
relaxates to the state 4I13/2 and the excess energy transfers back to the donor. The back
energy transfer increases with the concentration of dopant ions, since the distance
between the donor and acceptor ions reduced. At very high dopant ions
concentrations, the excitation is also beginning to migrate by donors, which is a
negative thing, because it leads to a decrease the acceptor ion pumping, a substantial
decrease in the lifetime of the luminescence level and thus worsening the energy
characteristics of up-conversion.
According to our experimental results, the dopant concentration 10%YbF3 1%ErF3 is
optimal and the quantum yield for this sample is maximum. When the concentration
of dopant is higher, this leads to decrease the distance between the donor and
acceptor and reduction the lifetime and the intensity of the up-conversion
luminescence.
Adding an Tm3+ ions can change the color of up-conversion emission, and obtain white
luminescence. However, the investigated sample has low irradiation intensity and it
requires more carefully optimization of the dopants concentrations ratio.
Conclusion
• A system for the acquisition of up-conversion luminescence kinetic
characteristics using non descanned regime of microscope Carl Zeiss LSM
710 NLO was developed.
• We have established correlation between the dopant composition and upconversion luminescence lifetime as well as up-conversion luminescence
intensity from levels of Tm3+ 1G4 → 3H6, ~470 nm (blue),
Er3+ (2H11/2, 4S3/2) → 4I15/2 ~ 530 nm (green), and 4F9/2 → 4I15/2, ~ 650 nm (red).
Based on these results, were made assumptions for the mechanism of
radiative levels of Er3+, Tm3+ population.
• The optimal concentration of up-converting doping ions for convert infrared
radiation into a visible for ghost matrices SrF2 is 10%YbF3/1%ErF3. The
quantum yield in visible range for this sample was 0.42%.
This work was supported by grants from the
President of the Russian Federation (MK №
4408.2011.2) and MES (activity 1.2.2,
research groups led by candidates: №
14.740.12.1343 from 10.03.2011)
Thank you for your
attention!