Journal of Luminescence 33 (1985) 261 —272 261 North-Holland, Amsterdam FLUORESCENCE ENHANCEMENT INDUCED BY THE PRESENCE OF SMALL SILVER PARTICLES IN Eu 3~ DOPED MATERIALS O.L. MALTA, PA. SANTA-CRUZ, G.F. DE SA and F. AUZEL * Departamento de Quimica Fundamental e Departamento de flsica da UFPE, Cidade Universitària — Recife — PE— 50000, Brash Original manuscript received 20 August 1984 Revised manuscript received 26 December 1984 We study the effect of small silver particles on the emission spectrum of Eu3~ doped materials. Depending on the excitation frequency and the concentration of silver particles embedded in the host material, a significant enhancement of the fluorescence from the Eu3~ions is observed. This experimental observation corroborates the importance of the long-range electromagnetic interaction between the plasmons on the silver particles and the host medium. A theoretical analysis based on the electromagnetic model is made and satisfactory agreement with experiment is obtained. 1. Introduction The intensities of 4f *-* 4f transitions depend strongly on the nature and the structure of the chemical environment around the rare-earth ion. This is due to the fact that these lines are forbidden by Laporte’s rule and therefore their intensities are subjected to second-order mechanisms. Among these, we may emphasize the forced electric-dipole and Pseudo-Multipolar Field (PMF) as the relevant mechanisms, in most cases, in the theory of 4f ~-* 4f transitions [1—3]. Since the discovery of SERS (Surface-Enhanced Raman Scattering) [4] several studies, both experimental and theoretical, on the optical properties of molecules deposited on a rough metallic surface have appeared [5—9].Up to date, the general conclusion of these studies is that certain conditions of roughness of the metallic surface are necessary for the observation of SERS and that the SERS phenomenon can be satisfactorily described by the electro- magnetic interactions between the molecules and the roughness of the surface, even though there is some experimental evidence that chemical effects also contribute to the phenomenon [9]. These results suggest a study of the effect of metallic particles, grown in the bulk of a rare-earth material, on 4f ~-‘ 4f transitions. As in the work of Weitz et * On leave of absence from CNET 196 rue de Paris, 92220 Bagneux, France. 0022-2313/85/$03.30 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)