ENHANCEMENT OF Nd3+ EMISSION BY Cr3+ COACTIVATION IN NEW LASER GARNETS

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ENHANCEMENT OF Nd3+ EMISSION BY Cr3+

COACTIVATION IN NEW LASER GARNETS

C. Garapon, A. Monteil, G. Boulon

To cite this version:

C. Garapon, A. Monteil, G. Boulon. ENHANCEMENT OF Nd3+ EMISSION BY Cr3+ COACTIVA- TION IN NEW LASER GARNETS. Journal de Physique Colloques, 1987, 48 (C7), pp.C7-493-C7-495.

�10.1051/jphyscol:19877117�. �jpa-00226934�

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JOURNAL DE PHYSIQUE

Colloque C7, suppl6ment au n012, Tome 48, dkcembre 1987

ENHANCEMENT OF ~ d EMISSION BY ~ + cr3+ COACTIVATION IN NEW LASER GARNETS

C. GARAPON, A. MONTEIL and G. BOULON

Laboratoire d e Physico-Chimie des Materiaux Luminescents, CNRS UA-442 et Celphyra, Universitd Claude Bernard, Lyon I , F-69622 Villeurbanne Cedex, France

The gadolinium gallium garnets Gd3Ga5012 (GGG), substitued by scandium Sc3' in the octahedral site (GSGG) is known as a laser material with an efficiency twice that of YAG:Nd?+, when it is codoped with Nd3+ and Cr3+ [I]. We have studied similar garnets, substitued by various cations Zr4+, CaZt, MgZ+ which should have similar intermediate crystal field at the Cr3+ site. First results have been given in 121.

EMISSION SPECTRA

GGG(Ca Mg Zr):Nd laser transition

(Gd.Ca)g(Ga.Mg.Zr)2Ga3012 : Nd3+

The Nd3+ 4 F 3 ~ - + 4111/2 fluorescence spectra are slightly different for GGG-Ca, Mg, Zr (CMZ). GGG-Ca, Zr (CZ) and GGG-Mg, Zr (MZ) (figure 1) due to slightly different ^*F312 splitting (table 1).

However they are all charac- terized by broad lines relative to other garnets. These large line width are due to the various substituting cations inducing sites of slightly different crystal field strength. This inhomogeneous broadening has two important consequences for laser applications relative to YAG and GSGG : emission cross-section is decrea- sed, allowing greater energy storage and the concentration quenching occurs at higher concentrations (table 1).

The measured parameters are in

X(pm) 1112 1.10 108 1.06 1.04 reasonable agreement with

previous data on CMZ and

CZ

[31.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19877117

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C7-494 JOURNAL DE PHYSIQUE

hmax(~) C(1max) 'I 4F3/2 splitting line width

Nd/cm3 Crs cm- 1 A

Y

AG* 1.064 1.4 1020 250 85 7

GSGG 1.061 2. 1020" 260 6 3 14

GGG-CMZ 1.061 2.5 1020 270 70 2 4

GGG-CZ 1.061 3 . 1 0 2 0 220 6 1 24

GGG-MZ 1.06 1 - 230 75 24

Table 1 - ~ d 3 ' fluorescence parameters in some garnets. (* literature) (Gd.Ca)3(Ga.Mg.Zr)2Ga3012 : Cr3+

For all three garnets the Cr3' emission is cons- titued of the 4T2 + 4A2 band at room tempe- rature and at 4.4K the 2E -, 4A2 line with side bands and the 4T2 -+ 4A2 band (figure 2). This indicates that the Cr3' ions are located in octahedral sites of inter-

E - 4 ~ mediate crystal field.

Furthermore excitation spectra and FLN experiments have shown that there are two kinds of multisites (submitted to

6000 7000 8000 publication).

(Gd.Ca)3(Ga.Mg.Zr)2Ga3012 : Nd3+. Cr3+

In codoped crystals Cr3' -, Nd3+ energy transfer occurs both radiatively and non- radiatively : The Nd3+ absorption lines appear in the Cr3+ band and the global intensity strongly decreases (figure 3). The transfer efficiencies evaluated from the ratios of the Cr3' intensities without and with Nd3' are of the order of more than 90%. The non- radiative transfer efficiencies En, evaluated from the mean Cr3' decay times are less important (table 2 ) but similar for all the garnets studied here.

However the enhancement of the Nd3+ fluorescence intensity due to the sensitization by Cr3' depends strongly on the nature of the garnets. The ratio of the intensity at 1 . 0 6 ~ with Cr3' against that without Cr3+ is of the order of 6-7 for GGG and GSGG but is only 1.5 for

CZ.

For MZ and CMZ it is even less than 1. An increase of 40% is observed for CMZ only for single crystal sample.

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Absorption of Neodymium

emission band of Chromium

Fig. 3

The fluorescence decays of Nd3+ have a maximum located at about 4 0 ~ s . The mean transfer time evaluated from the Cr3+

decays are shorter for the GGG (CaMgZr) ( 1 6ys) than for GSGG and GGG. Due to this fast transfer these materials should be interesting for applications to pulsed lasers.

p

.

powder c : crystal

Table 2 - ~ d 3 + 1 . 0 6 ~ fluorescence intensity I with cr3+ versus the intensity without cr3+ 10, non- radiative transfer efficiency and mean transfer time for different garnets of similar doping concehtrations.

However the reasons why the energy transfered by Cr3+ is lost in a large part for the Nd3+ fluorescence are not clear. Non-exponential Nd3+ fluorescence decays, faster than the Nd3+ decays without Cr3+ suggest that it could be lost in part by transfer to impurities. Experiments on this behavior are underway.

References

i l l D. PRUSS, G. HUBER, A. BEIMOWSKI, V.V. LAPTEV, I.A. SHCHERBAKOV.

Y.V. ZHAPIROV. Appl. Phys B.28 355 (1982).

(21 G. BOULON, C. GARAPON, A. MONTEIL. Advances in Laser Sciences 11. Proceedings of the 1986 International Laser Science Conference. Seattle 2 1 -24 october 1 986.

[31 M.D. SHINN, W.F. KRUPKE, J.A. CAIRD, L.K. SMITH, R. UHRIN, R.F. BELT. Conference on Lasers and Electro-optics 2 1-24 may 1985. Baltimore