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Ultrafast Dynamics of CdTe Nanoparticles in Water Solution
M. Sanz, A. Douhal*
Departamento de Química física, Sección de Químicas, Fac. de Ciencias del Medio Ambiente,
Universidad de Castilla-La Mancha, Avda. Carlos III, S.N. 45071 Toledo (Spain)[email protected]
Miguel , M.A. Correa-Duarte, L. M. Liz-MarzánDepartamento de Química Física, Universidade de
Vigo, 36310 Vigo (Spain).
Trans HYZTrans AZO
Cis HYZ
< 30 fs < 1 ps
1 ps (solvent)2 – 15 ps (cavity)
4 ps (solvent)15 – 200 ps (cavity)
S1
So
PNAS, Dec. 2006
Femtochemistry in Nanocavities
Size-dependent luminescence of as-prepared CdTe NCs(concentration of CdTe disperse solution was 0.4 mM, calculated by added amount of NaHTe). The emission color of TGA-stabilized CdTe NCs can be adjusted by their sizeto be cyan, green, yellow, orange, red, and dark red underthe radiation of the UV lamp (left). The colors of the samples were also observed in sunlight (right).
Jia Guo, Wuli Yang, and Changchun Wang*J. Phys. Chem. B, 109 (37), 17467 -17473, 2005.
Living breast cancer cells adherentat the bottom of the flow channelwhich are located (A) 11 mm away, (B) 5 mm away, and (C) just abovethe edge of the permanent magnet. Capsules taken up by the cells are recognizable by their luminescence. All pictures were obtained by overlay of phase contrast andluminescence images; the luminescence of capsules isdetermined by CdTe nanocrystalsand is shown in pseudocolored red.From: W. J. Parak et al., Langmuir, 21 (10), 4262 -4265, 2005.
Under the microscope (5 nm)
CdTe in Water Solution
400 500 600 700 800Wavelength (nm)
0
0.4
0.8
450 500 550 600 650 700
0,0
0,2
0,4
0,6
0,8
1,0
reaction time
(Size dependent on reaction time)CdTe
1,5 h 20 h
Inte
nsity
(u.a
.)
Wavelength (nm)
371 nm
Cd Te 20 horas segunda reciente 23-11-2004 exc=371 nm
630 nm600 nm580 nm540 nm520 nm
0
2000
4000
6000
8000
10000
Cou
nts
0 1 2 3Time (ns)
520 560 600 640 680 720Wavelength (nm)
100 ps200 ps300 ps500 ps1 ns2 ns5 ns10 ns15 ns20 ns
0
10000
20000
30000
40000
Inte
nsity
PICOSECOND OBSERVATION
0
2000
4000
6000
8000
10000
Cou
nts
0 1 2 3Time (ns)
0
2000
4000
6000
8000
10000
Cou
nts
0 1 2 3Time (ns)
630 nm
Size effect on the ps decays of CdTe in Water.
RED: 3 nm, Black: 5 nm and Exit at 371 nm (40 ps).
520 nm
40, 500-700 ps AND 15-25 ns
ESQUEMA DEL SISTEMA DE MEDICIÓN DE DINÁMICAEN FEMTOSEGUNDO, RESOLUCIÓN TEMPORAL, 30 fs
Contador de fotones
Osciloscopio
Láser de FemtosegundoOscilador
~ 60 fs, 82 MHz, 550 mW
Autocorrelador
CN
M
P
DobleMonocromador
SPD
ω0
ω0
ω2
ED
Línea de retraso, 6.5 fs
GTH
ω0,2
E
LLF
CN
E: Espejo; ED: Espejo Dicroico; M: Muestra (Célula rotatoria); P: Polarizador L: Lente; F:Filtro; CN: Cristal No Linear (BBO); GTH: Generador de Tercer Armónico; FD-E: Fotodiodo – Espectrómetro.
Resultado (fs-ps)
Tratamiento
Control Espectral
Control Temporal
0 2000 4000 6000 8000 10000Tiempo (fs)
0
2000
4000
6000
8000
10000
Cue
ntas
266, 400 y 800 nm
Bombeo
1- La INTENSIDAD de la señal es función:
i) del tiempo de RETRASO entre el láser sonda y la emisión de la muestra.
ii) de la INTENSIDAD del LÁSER sonda.
2- La RESOLUCIÓN TEMPORAL depende de los láseres de bombeo y de sonda, de la óptica, PERO NO de la electrónica.
3- La RESOLUCIÓN ESPECTRAL depende del cristal no lineal, del monocromador, y de la óptica.
Retrasotemporal τ
Pulso láser sonda
fs-Excitación Fluorescencia
0 t
0 t
∫∞
∞−−= dttItII laserflsuma )()()( ττ
FluorescenciaCristal No Lineal
Láser sonda
Suma de frecuencias νsum = νláser + νfluo
PRINCIPIO: Óptica No LinealExcitación Láser
INFORMACIÓN INTÍMA SOBRE LA MATERIA
0 2 4 6 8Time (ps)
0
2000
4000
6000
8000
Cou
nts
470 nm
500 nm
540 nm
600 nm
630 nm
580 nm
0 2 4 6 8Time (ps)
0
2000
4000
6000
8000
Cou
nts
460 nm
500 nm
540 nm
580 nm
620 nm
3 nm 5 nm
Femtosecond observation
0
2000
4000
6000
8000
10000C
ount
s
0 4000 8000 12000Time (fs)
NO Fluence excitation effect on CdTe (5 nm in diameter)transients observed upon 60 fs excitation at 371 nm and
gating at 580 nm.
5 mW (Black)45 mW (RED)
0
2000
4000
6000
8000
10000C
ount
s
0 4000 8000 12000Time (fs)
NO solvent-isotope effect on CdTe (5 nm) transients observedupon 60 fs excitation at 371 nm and gating at 630 nm
D2O (Black)
H2O (RED)
0
200
400
600
800
1000
Cou
nts
0 1 2 3Time (ps)
IRF
470 nm
CdTe in water, 5 nm, excit at 371 nm 60 fs.
CdTe 5 nm Exc=368 nm fs
λ (nm) τ1 (fs) % τ2 (ps) % τ3 (ps) % χ2
470 120 100 1.682
500 150 98 1.8 2 2.506
540 325 82 1.4 9 40* 9 1.484
580 150 -47 1.7 20 40* 33 1.805
600 200 -49 1.4 15 40* 36 2.263
630 320 -51 1.2 27 40* 22 2.003
CdTe 3 nm exc=368 nm fs
λ (nm) τ1 (fs) % τ2 (ps) % τ3 (ps) % χ2
470 120 100 2.394
500 280 82 1.8 13 40* 5 1.251
540 200 34 1.5 54 40* 13 1.065
580 200 -47 1.7 37 40* 16 2.376
620 260 -47 1.5 19 40* 34 2.335
520 560 600 640 680 720Wavelength (nm)
100 ps200 ps300 ps500 ps1 ns2 ns5 ns10 ns15 ns20 ns
0
10000
20000
30000
40000
Inte
nsity
- 120 - 350 fs (+ and -)- 1 - 2 ps- 40 ps
0 2 4 6 8Time (ps)
0
2000
4000
6000
8000
Cou
nts
3 nm
5 nm
500 nm
630 nm
Ps- TRES
- 0.5 - 0.7 ns for both sizes
- 14 - 17 ns for 5 nm size- 18 - 25 ns for 3 nm size
Model of ultrafast exciton dynamics in CdTe NPs. Electrons (filled circles) are promoted to the conduction band(CB) by absorption of light of the appropriate energy, leaving a positively charged hole (emptycircles) in the valence band (VB). Twocompeting pathways for emission are available through the band edge anddeep trap routes with short (I) andlong (II) time scales.
I) The initial band edge emission ( BE) results from the immediate recombinationof the electron and hole after excitation. In the deep trap case, an electron froma surface (SS) immediately relaxes to the valence band to radiatively combine with the original photogenerated hole giving rise to the near-IR deep trapemission ( DT).
(II) The long-lived emission at band edge wavelengths results from the excited-stateelectron relaxing to a triplet state (TS) with an energy close to that of the lowestelectronic excited state in the conduction band. Electron migration from the conduction band to the surface hole (or vice-versa) gives rise to the extended deep trap emission.
CONCLUSION
-First observation of femtosecond dynamics of confined CdTein water solution.
-Highly stable under fs-excitation.
-Components of 150-350 fs as decay and rise: connected states by a ultra fast non-radiative channel.
-Increasing the size of the nanoparticle decreases the emission lifetime, most probably to a decrease of the energy gap.- … Might be important for a better design of nanoparticles to nano and biotechnology.
Thanks: MEC for the financial support.