Upconversion and White Light Generation Properties of Undoped and Yb3+ doped Yttrium Silicate Nano-Phosphors

H. Cinkaya, G. Eryurek, B.D. Bartolo
Boston College,
United States

Keywords: sol-gel, white light, upconversion, nanopowders

Summary:

The optical systems that consist of rare earth ions embedded in a host lattice are very interesting materials for many applications such as optical sensing, data storage, nonlinear imaging and biomedical applications [1, 2, 3]. Upconversion process generate one high energy photon out of two or more low energy photons. The transitions possible between different energy levels of a rare earth ion have spectral line shapes that described by the Dieke diagram [4]. Yttrium silicates (YSO) are suitable host materials for the RE ions because of their high thermal and chemical stability [5, 6]. In the present study, we have investigated the properties of yttrium silicate nanopowders undoped and doped with 5% and 10% (per mole) Yb3+. The samples were obtained by the sol-gel method and annealed at 1250 0C for 12 hours. After the annealing process, the nanopowders were structurally characterized by X-Ray Diffraction (XRD) and Scanning Electron microscopy (SEM). The ascertained size of the nanopowders was ~ 80 nm. We have studied the emission from these samples when excited with the light of a near infrared laser diode at 975 nm. Luminescence spectroscopy is particularly apt at measuring peculiar aspects of nanopowders. As for the 5% and 10% per mole Yb3+ doped Yttrium silicate samples we have observed up converted emission at ~ 475 nm, ~ 520 nm, ~ 653 nm, and ~ 710 nm due to f-f transition of Yb and Er impurities [6]. by using 0.38 watt of laser power. Increasing the power of the laser, the emission loses its detailed structure and eventually presents approximately the spectrum of white light. We shall present a physical explanations for these effects.