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Sol-Gel

September 2000

YVO4:Ln (Ln= Eu, Nd) luminescent nanoparticles

by 
Arnaud Huignard*, Thierry Gacoin and Jean-Pierre Boilot
Solid State Chemistry Group, Laboratory of Physics of Condensed Matter,
Ecole Polythechnique, Palaiseau, France
*Contact address: ah@pmc.polytechnique.fr

This is a summary of the results presented at the "18th workshop of French Luminophores Group" March 2000, University of Lyon I. The complete list of presentations can be found online at the following address: http://www.univ-bpclermont.fr/LABOS/lmi/gfl/gfl18.htm


Introduction

Inorganic luminescent materials have practical applications in a variety of devices from conventional TV to electroluminescent, plasma or field emission displays. Moreover, the explosive growth of optical communications increased the demand for high performing luminescent materials in the area of solid state lasers.

Traditional techniques make use of high temperatures solid state reactions for the obtention of luminescent materials and leads to agglomerates of 5 to 20 µm in size.

Sol-Gel and colloidal chemistry proves to be a powerful technique to control the size of the ultimate grains of the material giving the freedom to the researcher to tailor and better control the final structural parameters which have an impact on the luminescent efficiency.

Bulk materials with strong luminescent properties are usually oxides doped with lanthanides or transition elements :

Y2O3:Eu3+, Y3Al5O12:Nd3+ (YAG), Al2O3:Cr3+

Recently an intensive research effort was directed towards chalcogenides core-shell nanostructures or doped semiconductor nanoparticles with a narrow particles distribution and high luminescent quantum yield.

CdSe/ZnS (1-3),  ZnS/Mn(4), CdS/Mn(5-6)


Advantages of using nanoparticles 

 

1. They can replace in most of the case instable organic chromophores used as luminescent probes in a variety of applications (biology).

2. They can be incorporated in a solid matrix (hybrid, sol-gel, etc) and used for optical device as bulk or films

3. High transparent material can be made by the appropriate chose of the nanoparticles size and refractive index.

4. Surface chemistry, doping and size control should lead to improved luminescent performances.

 

Bulk YVO4

Doped YVO4 (7-8) exhibits a high luminescent efficiency and it remains a good example for comparison.

The table below shows the wavelength of emission in respect to the dopants used:

 

LanthanidesEmission wavelength (nm)Application
Eu614-617Luminophore
Dy572Luminophore
Nd1060Lasers

YVO4 Structure

The structure of Orthovanadates is of Zircon type (Quadratic (a = b = 7,23 Ĺ, c = 6,29 Ĺ))

YVO.gif (9000 octets)

 

YVO4: Ln Synthesis

YVO4 was synthesized by aqueous co-precipitation reactions from Y 3+ Ln 3+ and VO43- salts in water (Figure1). The details of the procedure can be found in (9)

 

synth.gif (6809 octets)

 

Figure 1 :Aqueous co-precipitation

 

The colloidal suspensions of Ln: YVO4 nanoparticles was obtained by dispersing the precipitate using sonification and stabilization of the particles with sodium hexametaphosphate.

 

. col.gif (4424 octets)

 

To achieve purification and improve its stability, the obtained colloidal suspension is then dialyzed in pure water for 12 hours. 
The Colloidal solutions those prepared remain stable for several months in a large pH range (4< pH < 12)

 

Nanoparticles structure

 

High resolution transmission microscopy shows an ellipsoidal geometry with characteristic dimensions of around 15 and 30 nm.

tem.gif (71735 octets)

 

Luminescent properties

 

Under UV excitation, the colloidal solution shows a bright emission at 615 nm which is associated to the 5D0 - 7F2transition of the Eu 3+ ions (figure2)

 

sol.gif (29289 octets)solcol.gif (39821 octets)

 

Figure 2 : Colloidal solution of   Y0.95Eu0.05VO4 (5*10-4 mol.l-1) before and after UV excitation

Quantum efficiency


Measured quantum efficiency (15 %) remains however far below the bulk material . This low QE is presumably due to the high water presence at the particles surface. OH groups are well known luminescence quencher centers. 

Quantum yield was found to increase with both D2O<-> H2O exchange and hydrothermal annealing. Both luminescence QE and lifetime effects are shown below

 

Quantum efficiency

qe.gif (5161 octets)

 

Lifetime

 

ddv.gif (5204 octets)

 

Surface effects

OH impact on the luminescence properties of nanoparticles was evaluated by considering a core-shell model where the shell is fully hydrated and therefore completely quenched ( QE of shell =0). Assuming that  the Core quantum efficiency is similar to the one obtained with Deuterated samples (Core QE = QE (D2O)) then one can calculate  that 50 % of the Eu atoms are in 3 nm fully hydrated shell and completely quenched.

coc.gif (4363 octets)

 

 

YVO4:Nd Case

Colloidal solution of  Y0.98Nd0.02VO4 (0,2 mol.l-1)

Surface effects

em.gif (5809 octets)surf.gif (4417 octets)

 

These measurements have been made in collaboration with P. Aschehoug et B. Viana,

of Solid State Applied Chemistry Laboratory, ENSCP, Paris

 

Nanocomposites materials

Nanocomposites materials can be easily prepared by incorporating the YVO4:Ln stabilized nanoparticles on a silica sol-gel made precursor. Both  dip or spin coating techniques can be used.

nanocom.gif (8865 octets)

 

film.gif (69625 octets)

 

Summary

A very simple and efficient chemical route to prepare high luminescent colloids with controlled composition has been presented. Nanoparticles those formed can easily assembled as thin films by dip or spin coating techniques. They are water soluble and biocompatible. In comparison with organic dyes and semiconductor QD, they are narrower in spectral line width and probably more stable against photobleaching. 
Further studies are directed towards better size, crystallinity and surface molecular grafting control.

References

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8. R.C. Ropp
Luminescence and the Solid State, Elsevier, 1991
9. A. Huignard, T. Gacoin, J-P. Boilot
Chem. of Materials, 12 (4), 2000, 1090

 

Selected bibliography on semiconductors Quantum Dots 


YVO4

Wet-chemical synthesis of doped colloidal nanoparticles: YVO4 : Ln (Ln = Eu, Sm, Dy).
Riwotzki, K., Haase, M., J. Phys. Chem. B 102(50): 10129-35 (1998).

CdX, ZnX

Synthesis and characterization of CuxS nanoparticles: nature of the infrared band and charge carrier dynamics
M.C. Brelle, C.L. Torres-Martinez, J.C. McNulty, R.K. Mehra, and J.Z. Zhang, 
Pure and Appl. Chem. 72, 101, 2000.

Luminescece decay kinetics of Mn2+-doped ZnS nanoclusters grown in reverse micelles,
B.A. Smith, J.Z. Zhang, A. Joly, and J. Liu,
Phys. Rev. B, 62, 2021-2028, 2000.

Inorganic Quantum Dot – Organic Dendrimer Nanocomposite Materials,
K. Sooklal, J. Huang, C. J. Murphy, L. Hanus and H. J.Ploehn,
Mater. Res. Soc. Symp. Proc. 1999, 576, 439.

Luminescence of CdS Nanoparticles Doped and Activated with Foreign Ions,
J. M. Huang and C. J. Murphy,
Mater. Res. Soc. Symp. Proc. 1999, 560, 33.

Luminescence Spectral Properties of CdS Nanoparticles,
J. R. Lakowicz, I. Gryczynski, Z. Gryczynski, and C. J. Murphy,
J. Phys. Chem. B 1999, 103, 7613.

Layer-by-layer assembly of thin film Zener diodes from Conducting Polyelectrolytes and CdSe Nanoparticles.
T. Cassagneau, T. E. Mallouk, J.H. Fendler,
J. Am. Chem. Soc., 120(31), 7848-7859 (1998).

The Effect of Cadmium Ion Adsorption on the Growth of CdS Nanoparticles at Colloidal Silica Particle Interfaces in Binary Liquids
I. Dékány, L. Turi, G. Galbács, and J.H. Fendler,
J. Coll. Interf. Sci.,195, 307-315, (1997).

Coupled Composite CdS-CdSe and Core-Shell Types of (CdS)CdSe and (CdSe)CdS Nanoparticles
Yongchi Tian, Theresa Newton, Nicholas A. Kotov, Dirk M. Guldi, and Janos H. Fendler,
J. Phys.Chem., 100, 8927-8939 (1996)

High Temperature Optical Studies of CdS Nanoparticles
H Yükselici and P D Persans,
J Non-Cryst. Sol., vol. 203, 206 (1996)

Optical studies of the growth of Cd[1-x]Zn[x]S nanocrystals in borosilicate glass,
H. Yukselici, P. Persans, and T. Hayes,
Phys. Rev. B, vol. 52, pp. 11763, 1995.

Unusual Photoluminescence of Porous CdS (CdSe).
R. Tenne, V. Nabutovsky, E. Lifshitz, and A.F. Francis,
Solid State Commun, 82, 651 (1992).

Photochemistry of Colloidal Semiconductors.Onset of Light Absorption as a Function of Size of Extremly Small CdS Particles
H. Weller, H. M. Schmidt, U. Koch, A. Fojtik, S. Baral, A. Henglein, W. Kunath, K. Weiss, E. Diemann
Chem. Phys. Lett. 124 (1986) 557 - 560

Photochemistry of Colloidal Metal Sulfides.
8. Photo-Physics of Extremly Small CdS Particles: Q-State CdS and Magic Agglomerations Numbers
A. Fojtik, H. Weller, U. Koch, A. Henglein
Ber. Bunsenges. Phys. Chem. 88 (1984) 969 - 977

 

 

RELATED LINKS
More online papers from the same workshop on luminescent sol-gel made materials

Reference material on YVO4

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