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December 2000

Rare Earth doped transparent glass-ceramics

M. Mortier1, M. Génotelle1, G. Patriarche2
1Groupe d'Optique des Terres Rares, CNRS-UPR211
1, place Aristide Briand, 92195 Meudon cedex
2France Telecom R&D, 196 avenue Ravera, 92225 Bagneux cedex

 

 



Context and motivations

Research of new rare earth-doped active optical materials for photonic applications

 

Material choice: Glass containing fluorine in close proximity to the rare earth

Why fluorine ?

High solubility of the Rare Earth

lack of cluster initiating energy transfers

Weak phonon energy

low probability of non radiative transition

Why glass ?

High durability
Easy to produce (in the air)

Germanate glass of the family :

(50GeO250-yPbOyPbF2+xErF3)

y, y=[10,20] x=[0,4]

 

Other oxyfluoride systems explored:
  • PbGeO3-PbF2-CdF2
  • SiO2-PbF2

  • SiO2-Al2O3-PbF2-CdF2-YF3

Preparation of the samples

melting of the powders in a platinum crucible at 1000°C during 15 minutes in the air
quenching of the liquid between two copper plates
thermal analysis (DTA) of the as-melted glass
thermal treatment according to the DTA results

 

Preparation of polycrystalline PbF2 samples by very slow 
cooling of a liquid from 875°C down to 20°C in the oven of an argon glove box

Results

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Structural characterization of the glass-ceramic

 

Transmission electron microscopy

 

X-ray diffraction pattern

 

 

 

 

 

 

 

 

 

 

Volume crystal phase estimated smaller than 3%

 

Structural characteristics of the nucleation–growth glass-ceramics

 
    Cubic crystals of PbF2 (phase b )
    Average size of crystals determined by the composition of the precursor glass (x,y) and thhe thermal treatment
    Complete segregation of ErF3 in PbF2 (X-microanalysis)
    volume crystalline phase estimated smaller than 3% from electron microscopy and density measurements


Composition of the glasses:
50GeO250-yPbOyPbF2+xErF3

Absorption & emission cross-section of the 4I15/2® 4S3/2 transition versus  Temperature. 

Reduction of the inhomogeneous linewidth induced by the segregation of the rare earth in the crystal phase : w ® w /2.6 at 10K and increase of the maximum cross-section of the transition

 


 

Level scheme of the Er3+ ion


 

 

Fluorescence lifetime measurements of the (4I11/2® 4I13/2) transition

After excitation at 970nm

 

strong increase of the lifetime by the ceramisation

same decay profiles for the glass doped with 2 mol%Er after treatment and for polycrystalline PbF2 doped with 16.6  mol % Er

high local doping level in the crystallites limiting the lifetime increase obtained by the local crystallization (see decay 1mol%)

 

Evolution of the fluorescence decay of the 4I11/2® ® ® ® ®4I13/2 transition with the treatment duration

 

 

 

 

 

 

 

 

 

 

 

Evolution of the crystallisation with the thermal treatment duration

 

 

 

 

 

 

 

 

 

 

 

Lifetime of the erbium in the glass and in the crystallites of the glass-ceramic (50GeO240PbO10PbF2)

ErF3 in the glass(mol%)

ErF3 in PbF2 (mol%)

t 4I11/2 (ms)
glass

t 4I11/2 (ms)
glass-ceramic

WNR (s-1)
glass

WNR (s-1)
Glass-ceramic

2

20

0.25

3.8

3890

97

4

40

0.23

2.4

4200

303

 

ErF3  
in the glass (mol%)

t 4I13/2 (ms)
glass

t 4I13/2 (ms)
glass-ceramic

2

5.7

6.6

4

3.4

4.6

Increase of the fluorescence lifetime of the erbium ions mainly by the strong reduction of the non radiative contribution (WNRµ w coup) induced by the modification of the environment of the rare earth

  • in the starting glass: oxide glass of phonon cut-off frequency w coup=1000cm-1

  • in the glass-ceramic: fluoride crystal of phonon cut-off frequency wcoup=336 cm-1

 

Conclusions

Highly transparent material: small size of crystallites << l

Control of the devitrification

  • size and density of crystals function of the composition (x,y) and thermal treatments 50GeO2(50-y)PbOyPbF2+xErF3

Complete segregation of RE ions in the crystal phase

  • reduction of the inhomogeneous linewidth

  • net increase of the maximum cross-section

Increase of the fluorescence lifetime between the starting glass and the glass-ceramic

Conservation of the macroscopic properties of an oxide glass (isotropy, chemical durability, easy elaboration)

Discontinuity of density between glass (6.68g/cm3) and nanocrystallites (7.77g/cm3)

Step of refraction index between the glass (n=1.65 at 589nm) and the nanocrystallites 
(nb PbF2=1.835)

 

REFERENCES


M. Mortier and G. Patriarche, Journal of Materials Science 35(19) 4849-4856, October 2000

M. Mortier and F. Auzel, Journal of Non-Crystalline Solids 256&257 (1999)361-365

M. Mortier and F. Auzel, in Innovative Light Emitting Materials, P. Vincenzini and G.C. Righini editors, Techna Srl, 1999, 215-222

M. Mortier, P. Goldner, C. Château, M. Génotelle, Journal of Alloys and Compounds, to be published

 

Acknowledgements

F. Auzel is thanked for initiating the study of glass-ceramics in the Groupe d’Optique des Terres Rares (CNRS-UPR211).

Presented at "Journées Nanoparticules" October 19, Ecole Polytechnique, France

CONTACT THE AUTHORS : mortier@cnrs-bellevue.fr

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