Luz Visible En Nanofosforos

Progress In Electromagnetics Research Letters, Vol. 11, 139–148, 2009

BaZrO3 :Yb NANOPHOSPHOR FOR EFFICIENT UP-CONVERSION LIGHT EMISSION L. A. Diaz-Torres, E. de la Rosa, and J. Oliva Centro de Investigaciones en Optica A.C. Leon, Gto. 37150, Mexico P. Salas and V. M. Casta˜ o n Centro de F´ ısica Aplicada y Tecnolog´ Avanzada ıa Universidad Nacional Aut´noma de M´xico o e Boulevard Juriquilla3001, Quer´taro 76230, Qro. Mexico e Abstract—Strong visible green upconversion emission in nanocrystalline BaZrO3 :Yb3+ powder, obtained by a hydrothermal process at 100◦ C, is reported. The unconverted emission has a quadratic dependence on the pump intensity with a lifetime around half that of the NIR lifetime. Results suggest cooperative upconversion as the mechanism responsible for the greenfluorescence. This efficient Yb3+ -based cooperative up-conversion process allows the development of novel emitting materials in the ultraviolet to visible (UV-VIS) range.

1. INTRODUCTION Frequency up-conversion phenomena in trivalent Rare-Earth (RE) ions, hosted in a number of matrixes, have been widely investigated in the past two decades, due to their potential use as visiblewavelengthluminescent materials [1–11]. Indeed, Yb3+ -based upconversion phosphors are thought for applications ranging from biotechnology [1, 2] to high power lasers [3–5]. Since inexpensive near-infrared (NIR) pump sources, such as solid-state lasers and semiconductor laser diodes, are readily available nowadays, all kinds of NIR-to-visible up-conversion emissions and various energy-transfer processes based onthe use of Yb3+ have been investigated [6– 9]. Recently, detailed reviews involving Yb3+ as the base of upconversion processes in solids have been published by Auzel [10]
Corresponding author: L. A. Diaz-Torres (ditlacio@cio.mx).

140

Diaz-Torres et al.

and Gudel et al. [11]. More specifically, improved functionality related to Yb3+ in a nanosized host appears to be a promising area ofresearch [12, 13]. Particularly active is the search of new host materials with small multiphonon decay rates and good structural and chemical stability over a wide range of temperatures and corrosive environments. Perovskite materials have attracted vast attention due to their excellent optical, electrical, chemical properties and capability of hosting functional ions of various sizes [14–16]. Inparticular, oxides such as YAlO3 , BaTiO3 , LiNbO3 , and fluorides such as KMgF3 and NaYF4 have found important applications in visible-emitting phosphors when hosting Er and Yb ions [11, 17–20]. Oxides are quite resistant to corrosive environments and have good optical properties. However, most perovskites present phase transformations that lead to anisotropies in their refraction index, whichcauses non-linear optical phenomena such as second harmonic generation. For some high-energy upconversion applications, this represents a limiting factor, since the upconversion-generated heat can induce anisotropies, thus limiting the effective range of pumping power. Barium zirconate (BaZrO3 ) is a very promising refractory structural material with a very high melting point (2920◦ C) and low chemicalreactivity with corrosive compounds like the ones used in the fabrication of high temperature superconductors. Among the cubic oxide perovskites, BaZrO3 (BZO) is the only one that does not follow phase transitions over the range from 1600 K down to 4 K [21]. Recently, columnar inclusions of BZO nanocrystallites were found to enhance the transport currents in YBCO superconductors [22].Additionally, BZO has attracted attention as a promising candidate for protonic electrolytes in fuel cell applications [16]. Here, we report the NIR and visible (VIS) emission properties of nanocrystallites of Yb3+ -doped BZO (BZO:Yb), as powders synthesized by simple hydrothermal method. The strong green upconversion luminescence of BZO:Yb makes it a feasible candidate for visible light generation via...