Autumn School on Materials Science and Electron Microscopy 2007

"Microscopy - advanced tools for tomorrow's materials"

Berlin, October 8th - October 11th, 2007

PREPARATION, CHARACTERISATION AND LUMINESCENCE OF

NANOCRYSTALLINE

ββββ-Ga2O3:Er AND Y2O3:Ho

Tomislav Biljan1, Andreja Gajović

2 and Zlatko Meić

1

1Department of Chemistry, Faculty of Science, Horvatovac 102a, 10000 Zagreb, Croatia

2 Ruđer Bošković Institute, POB 180, HR-10002 Zagreb, Croatia

Luminescence from lanthanide doped materials has attracted much attention in recent years

[1], due to their use in the variety of applications in novel light emitting devices; such as

phosphors [2], solid state lasers [3], optical amplifiers and optical waveguides especially in

the NIR region where optical communication systems operate [1]. There has also been a lot of

interest in the use of lanthanide doped materials for up-conversion [4] of infrared to visible

light due to potential applications in photonics, optical data storage, lasers and sensors. Doped

lanthanide ions can also serve as a sensitive probe of chemistry and structure of host [5].

Particularly interesting is Er3+

with emission at 1.54 µm that corresponds to the wavelength of

minimal optical loss in silica based optical fibers [1].

Nanocrystalline β-Ga2O3:Er and Y2O3:Ho [6] have been synthesized by solution combustion

method using ethylene glycol as the fuel. Materials are characterized by using X-ray powder

diffraction (XRD) and transmission electron microscopy (TEM). Luminescence properties of

β-Ga2O3:Er and Y2O3:Ho are studied using two Raman spectrometers with excitation in NIR

and visible.

The variety in the shape and size of particles, in both β-Ga2O3:Er and Y2O3:Ho, was observed

by TEM (Fig. 1). The histogram of the particle size distribution (Fig. 2a) for β-Ga2O3:Er and

(Fig. 2b) for Y2O3:Ho confirms the predominance of the small particle sizes with a log-

normal distribution. The mean particle size calculated from the distribution was 16.9(5) nm

for β-Ga2O3:Er and 27.6(9) nm for Y2O3:Ho, which is in line with values of the average

crystallite size estimated from XRD measurements (21(3) nm for β-Ga2O3:Er and 25(2) nm

for Y2O3:Ho). The appearance of the rings in SAED patterns (inserts in Fig. 1) indicated

nanosized crystallites, as observed by TEM, and determined from broadening of the XRD

lines.

Luminescence properties have been studied by using Raman spectrometers with excitation in

NIR and visible. All bands present in spectra of β-Ga2O3:Er are assigned to 4f11

→ 4f11

transitions of Er3+

and bands present in spectra of Y2O3:Ho to 4f10

→ 4f10

transitions of Ho3+

.

Main characteristic of luminescence spectrum of β-Ga2O3:Er is a strong Er3+

NIR emission at

1.54 µm due to the 4I13/2 →

4I15/2 transition under the 1064 nm excitation. The intensity of this

technologically important transition can be significantly (around 60 times) increased by the

Yb3+

codoping. Main characteristics of luminescence spectra of nanocrystalline Y2O3:Ho are

strong emissions between 1120 and 1225 nm and 710 and 765 nm due to the 5I6 →

5I8 and (

5S2

+ 5F4) →

5I7 transitions of Ho

3+, respectively [6].

a) b)

Figure 1. TEM and SAED of: a) β-Ga2O3:Er and b) Y2O3:Ho

a) b)

Particle sizes / nm = 323*1*lognorm(x, 3.1788, 0.5181)

6 13 20 27 34 41 48 55 62 69 76 83 90 97

Particle sizes / nm

0

2

4

6

8

10

12

14

16

18

20

No

of

part

icle

s

Figure 2. Distribution of the particle sizes observed by TEM a) β-Ga2O3:Er and

b) Y2O3:Ho

[1] A. J. Kenyon, Progr. Quant. Electr. 26 (2002) 225.

[2] S. Ekambaram, K. C. Patil, M. Maaza, J. Alloys. Compd. 393 (2005) 81.

[3] W. Koechner, Solid-State Laser Engineering, Springer Verlag, New York, 1999.

[4] F. Auzel, Chem. Rev. 104 (2004) 139.

[5] A. Polman, Physica B. 300 (2001) 78.

[6] T. Biljan, A. Gajović, Z. Meić, E. Meštrović, J. Alloys Compd., 431 (2007) 217-220.