Fluorescence yield enhancement due to dispersed silver particles in Eu3+ doped glasses

Journal of Luminescence 40&41 (1988) 133 134 North-Holland, Amsterdam

133

3~DOPED GLASSES

FLUORESCENCE YIELD ENHANCEMENT DUE TO DISPERSED SILVER PARTICLES IN Eu G.F. DE sA, W.M. DE AZEVEDO and O.L. MALTA

Departamento de Quirnica Fundamental and Departamento de Fisica da UFPE, Cidade Universitária, 50.000, Recife, PE - BRASIL We present and discuss the fluorescence yield enhancement for Eu3~ ions, in glass materials contaming silver particles, as a function of the thermoreducing agent concentration. The experimental results can be satisfactorily interpreted in terms of plasmon excitations nearby the Eu3~ ions. 1. INTRODUCTION

xEu 2O3 (with x=O.O and 3.0%), yAgN)3 (with y=O.0

Recently, haveofobserved the first 1’2 that a we factor —6 can for be gained in tithe

and The 3.c~) and z5b203spectra (with z=0.O, and 3.0%). absorption of these1.5, samples were

me emission yield of the Eu3~ion if the glass material contains a bulk distribution of silver

recorded with a Beckman Acta CV double-beam spectrophotometer. All the spectra were obtai-

particles with an average diameter of 40A and a

ned using a sample without silver as the

particle concentration of 10’8cm3. The aim of this paper is to present the

rence. The fluorescence and excitation spectra were recorded by using a l.2m S~xmonochromator

perimental observation in which, for

a

exfixed

model 1269 with slits routinely set at lOOjim.

concentration of silver, the fluorescence enhan cement for the Eu 3+ ion varies as a function of the thermoreducing agent (antimony oxide)

con-

refe-

2.2 Results. Figure 1 shows the absorption spectra of the samples with 1.5 and 3.0% of Sb 2O3, respective—

centration in the glass material.

ly, and both with 3.0% of silver. The first point to be noticed is that in both cases two

2. EXPERIMENTAL

peaks are observed and their relative intensi-

2.1 Materials and Instrumentation, The glass samples preparation is essentially 1. The the same contained as alreadyin described mixture a platinumelsewhere crucible heated and melted at 1200°Cfor about

1

was hour.

ties is inverted from one case to the other. Secondly, the position of the lower peak remains practically unchanged while energy the higher energy one moves from 356nm to 325nm when

the

5b

The melt was then poured into a graphite molde,

203 concentration is doubled. Figure 2 shows the excitation spectra of the

pre-heated to 4000C, for annealing purposes . The high stability of the samples permits the

samples with and without silver for the two con centrations of 5b203. It may be noticed that d,~

redlization of subsequent annealings without destroying the sample characteristics. Host corn position was such that the weight of glass for— ming B203 and CaF2 was (CaF2+B203)/CaF2 = 1.43 and the doping concentrations by weight were

pending on the excitation wavelength d considerable fluorescence enhancement is obtained.Also the enhancement is more pronounced for the 1.5% 5b203 sample. An analysis based on these results together with the energy level distribution of

0022 2313/88/$03.50 © Elsevier Science Publishers BY. (North-Holland Physics Publishing Division)

134

G.F de Sá et al.

/ Fluorescence yield enhancement

(1)

z

I—

(a)~l,5%of Sb

203

(a)

(Cl

3% of Ag (b)~3% of Sb203

>-

/

>-

3%ofAg

3% of Sb203 and 3%ofAg

(d)= 3% of Sb203 and 0%ofAg

~‘

I.-

H (c)J

/

5 >-

--

H

‘Cd)

>-

H

z w H

z

(b)

(a)

1,5% of Sb2O3ond

H of Ag 1,5% of Sb203 and 3%

(b) I

300

400

,

500

600

I

/

(0)

=

0% of Ag

/

WAVELENGTH(nm)

(b)

-

FIGURE 1 Absorption spectra of CaF2-B203, 3% Eu~03, 3% AgNO3 glass as a function of antimonium concentration at room temperature. 3~ion can be made in order to rationalize the Eu this effect which represents a compromise ~

WAVELENGTH (A) FIGURE 2 Excitation (at 6l20i) spectra in CaF of the luminescence of

the enhancement of absorption and emission rates

2-B203 glass, as a function of Antimonium concentration at room temperature.

and quenching by the localized plasmons.

one point should be emphasized.

3. DISCUSSION

ved a dependence of the peak position and width of the absorption bands with the thickness of

2000

3000

4000

5000

6000

We have

Eu3+

obser-

The existence of two absorption peaks, as shown 3.in The fig.l, way have three possible explanafirst one is that, in the present tions case, the distribution of particle size is sharply peaked at two average diameters. Secondly,

the samples. This points to a nonuniform distribution of silver is an argument in favour of the particles first of and the it above explana-

the higher energy peak may be

terpreted in terms of the electromagnetic

light absorption by isolated Ag

attributed

to

neutral atoms

,

the lower energy one being attributed to the absorption by the plasmons in the silver particles. Thirdly, besides the formation of silver partides, clusters involving Sb3~, Ag+ and Eu3~ ions could absorb in the near U.V. In the latter two cases, the fluorescence enhancement would be due to energy transfer to the Eu3~ions while in the first case it would be due to plasmon exditatidris 3+ 1 nearby the Eu ions . Eventhough at the present state of our study we cannot distinguish between these mechanisms

tions. Actually, the fluorescence yield enhancement shown in fig.2 has been satisfactorily inmodel

as developped in ref.l. ACKNOWLEDGMENTS The authors are grateful to the CNPq

(Brazi-

han Agency) for financial support. REFERENCES 1. 0.L.Malta, P.A.Santa-Cruz, G.F. de Sá and Auzel, 3. of Luminescence, 33 (1985) 261. -

F.

2. 0.L.Malta, P.A.Santa-Cruz, G.E. de Sa and F. Auzel, Chem. Phys. Letters, 116 (1985) 396. 3. U.Kreibig, AppI. Phys., 10 (1976) 255.