Optical Properties Of Nanocrystalline Y2 O3:Eu3+

Optical properties of nanocrystalline Y2 O3:Eu3+
S. Ray and P. Pramanik

arXiv:cond-mat/0407519v2 [cond-mat.mtrl-sci] 11 Jan 2006

Department of Chemistry, Indian Institute of Technology, Kharagpur 721 302, West Bengal, India A. Singha and Anushree Roya) Department of Physics and Meteorology, Indian Institute of Technology, Kharagpur 721 302, West Bengal, India

Abstract
Opticalproperties of nanocrystalline red-emitting phosphor, Europium doped Yttria (Y2 O3 :Eu3+ ), of average particle size 15 nm are investigated. The intensity of the strongest emission line at 612 nm is found to be highest in the nanocrystalline sample with 4 at. wt. % of Europium. The narrow electronic emission spectrum suggests a crystalline surrounding in this nanomaterial. We have estimated the strength ofthe crystal field parameter at the dopant site, which plays a crucial role in determining the appearance of the intense emission line. The equilibrium temperature of this system has also been calculated from the intensity ratio of Stokes and anti-Stokes Raman scattering. Though known for the bulk samples, our approach and consequent results on the crystalline nanomaterial of Y2 O3 :Eu3+ provide aunique report, which, we believe, can be of considerable significance in nanotechnology.
PACS numbers: 81.07.Wx, 78.67.Bf

1

I.

INTRODUCTION

The optical properties of rare-earth ions trapped in inorganic oxides continue to be a research attraction in terms of both their fundamental and technological importance.1,2,3,4,5 Yttrium oxide doped with Eu3+ is one of the main red-emittingphosphors and is widely used in lighting industry and in solid-state-laser based devices.1,2,3 The unique optical properties of this material is based on the f - and d electrons of Europium ions. To enhance the brightness and resolution of displays in devices in the present nanotechnology regime, it is important to develop phosphors with controlled morphology and small particle size (nanoparticles).The potential of this low dimensional material in fabrication of modern micro/nano devices requires an understanding of their fundamental properties in detail. In particular, the origin and behavior of the strongest 5 D0 − 7 F2 transition spectrum from Eu3+ needs to be investigated because of its importance in designing laser devices. For example, permanent laser-induced gratings have beenfabricated using crossed write beams in resonance with the 7 F2 − 5 D0 absorption transition of Eu3+ .6 Over the last couple of decades, a considerable amount of work on the spectral properties of bulk Y2 O3 :Eu3+ has been reported in the literature.7,8,9,10,11,12,13,14,15 . Additionally, we find several articles on nanoparticles of this material, though, the detailed study of their optical properties is,as far as we are aware, incomplete. In recent times, Schmechel et al.16 have reported luminescence properties of nanocrystalline Y2 O3 :Eu3+ . However, due to the presence of defect/disordered states in this low dimensional system, the quantum efficiency of this nanomaterial is much less than the corresponding bulk commercial sample. Furthermore, Konard et al.17 have synthesized and studied theluminescence properties of Y2 O3 :Eu3+ nanoparticles, though they do not discuss the quantum efficiency of this material. In both these studies16,17 one does not find the details of the optical emission spectrum of this low dimensional system. Apart from optical properties, other characteristics of such inorganic, lanthanide-doped oxides also play an important role in using these materials in technology.Walsh et al.18 have recently demonstrated that the strength of the crystal field is crucial in improving the performance of solid-state lanthanide lasers. It may be noted that the doped Europium ions in these oxides provide the high-energy local mode phonons, which can produce structural modification of the host. Finally, the knowledge on the thermal properties of this material is 2

required...