Luminescence of Cerium (3+) activated rare earth silicophosphates

Luminescence of Cerium (3+) activated rare earth silicophosphates

Journal of Luminescence 40&41 (1988) 163 164 North-Holland, Amsterdam 163 LUMINESCENCE OF CERIUM (3+) ACTIVATED RARE EARTH SILICOPHOSPHATES * Zhup...

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Journal of Luminescence 40&41 (1988) 163 164 North-Holland, Amsterdam

163

LUMINESCENCE OF CERIUM (3+) ACTIVATED RARE EARTH SILICOPHOSPHATES

*

Zhupo HIJANG and Guoling MA Department

of Chemistry, Peking University, Beijing 100871, China

1. INTRODUCTION 3~ Terashima et al had ever reported that Th and Ce3~coactivated Lanthanum silicophosphates were good lamp phosphors1.

The emission, excitation and diffusive re— flectance spectra of Ce3~—activated LSP and GSP are shown in Fig.

1.

Rare earth silicopho—

sphates with a general formula RE 203O.lOSiO2~

(a)

O.95P205 (RE represents La or Gd and these for— mula are simplified as LSP or GSP respectively) were synthesized terials

and developed

for making phosphors.

/

as good host ma— A systematic

in—

vestigations on silicophoAphates the luminescence of properties 3~—activated lanthanum of and Ce gadolinium are reported.

(b)

100 LSP

I

I/

\

/

50 El

El

I

2. RESULTS AND DISCUSSION Samples of definite composition and single phase were prepared by solid state reactions. Their crystal structure were determined by x—ray diffractometer

330

l5OmA) to be mono—

D/maxra (40KV,

clinic and isostructural

“~



290

370



1~i0200 214.0 280

WAVELENGTH

(nm)

with GdPO 6 (ASTM 26—660).

The lattice parameters were calculated, and are shown in Table

FIGURE 1 Emission spectrum (A 254nm)(a), diffusive reflectance and excitagon spectrum (A 320nm)(b)

1.

of Ce(3’~).

em

TABLE 1. The lattice parameters of LSP and GSP

v(R

Their emission spectra consistdifference of a broadof band of two peaks with an energy 2000cm , corresponding to the transitions from excited Sd level to 4f 2F

3) parameters lattice a($.)

b(R)

c(R)

(~°

LSP

6.85

7.05

6.63

105.36

308.6

GSP

6.66

b.84

6.33

103.37

279.5

2F 3~. 712 and 512 of Ce There are two absorption bands in their excitation and diffusive reflectance spectra. The smaller band arisesfrom the host absorption and

The luminescence

and optical

properties

of the

samples were measured with a fluorescence spectra— meter type Hitachi

the larger

one,

230—3lOnm, orginates

from the 4f——5d transition.

It shows that these

850. two compounds

*

spanning

Project Supported by National Natural Science Foundation of China.

0022 2313/88/$03.50 ~ Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)

are highly efficient photolumine—

1 64

Z. Huang, G. Ma

/ Cerium

(3 +) activated rare earth srl,cophosphates

scence phosphors. The optimum concentrations 3~doped in the LSP and GSP are 0.2 and 0.6 of Ce mole% respectively. We have found

that

shift of sub—level2

there

of 2F

exists

the

293K

388K

L~23K

thermal

7/2 in the emission

spectrum of LSP:Ce3~ and GSP:Ce3~. Fig. 2 shows that the peak wavelength of Sd —2F 712 transition of LSP:Ce

at 298K shifts ca. 5nm toward short

wavelength from that at 77K.

300

3k0

300

31~0

300

34~0

WAVELENGTH( nm) FIGURE 3~ in3 the LSP at different Emission temperatures spectra 293K,of 388K Ce and 423K.

77K 298K

of the former decreases ca. 27% from 298K to 513K,

whereas that of the latter decreases ca.

7%. According

to Dexter’s theory3, preliminary 3+ study on concentration quenching of Ce ions in these phosphors has been made.

From the con-

centration dependence relationship of the emission intensity lgx—lgI/x were experimentally

220 300 380 WAVELENGTH(nm)

obtained.

We would consider that the concentra—

tion quenching of Ce3~ ions in these phosphors arises from the dipole—dipole interactions.

FIGURE 2 3+ Emission spectra of Ce in (La Ce ) 0 0.lSiO ~O.95P 0 at 77K and 293~8 0.2 2 3 2 2 ~ The temperature dependence of peak wavelength 2 — ~7I2 emission from 298K to 423K shows

of ‘Id

the same trend (Fig.

3) as from 77K to 298K,

that is it shifts to short wavelength a little,

whereas the peak wavelength of Sd _2F 5/2 emission does not change as the temperature is varied

in the range of 77—298K and of 298—423K.

This means that

energy

levels

of Sd 2F and 712 moves

remain unchanged, meanwhile that of

apart from Sd level as the temperature is raised. 3+ emissions The temperature of Ce from transitions of quenching 5d _2F 2F 5/2 and Sd _ behave differently.

The luminescence

7/2 also intensity

REFERENCES 1. K. Terashima, Y. Kimura and K.Kohmoto, Toshib~ Review, 37 (1982) 110—111. 2. Xu Ti—sun, Song Zeng—fu, Acta Physica Sinica, 35 (1986) 213. 3. D.C. Dexter, J. Chem. Phys.

21 (1953) 836.