Infrared excited YbEr: Y 2 O 2 S: phosphors with intense emission for lighting applications G.A.Kumar * , Madhab Pokhrel and D. K.Sardar Department of Physics and Astronomy, University of Texas at San Antonio, San Antonio, Texas 78249 ABSTRACT Yb and Er-doped Y 2 O 2 S phosphor was synthesized by solid state flux fusion method and their upconversion spectral properties were studied as a function of different Yb concentrations. The solid state flux fusion results in well crystallized hexagonal shaped phosphor particles of average size 3.8 μm. The detailed optical characterizations such as absorption, emission, and fluorescence decay were performed to explore the emission processes in the UV-VIS-NIR as well as to quantitatively estimate the fluorescence quantum yield. Upconversion spectral studies show that for all the compositions, green emissions are stronger, particularly; the green emission intensity is 1.7 times stronger than the red one with composition of 8 mol% Yb and 1 mol% Er. Mechanisms of upconversion by two photon and energy transfer processes are interpreted and explained. The color coordinates are measured and the color tunability was analyzed as a function of the 980 nm excitation power. Results show that the Y 2 O 2 S:Yb,Er phosphor offers power dependent color tuning properties where the emission color can be tuned from 490 to 550 nm by simply changing the 980 nm excitation power from 10 to 50 mW. Keywords: “Optical material, Absorption, Fluorescence, Upconversion, Infrared emission, Quantum Yield, Excited state absorption, Color coordinates” * Corresponding author: akgsh@yahoo.com 1. INTRODUCTION Luminescent materials attract a great deal of attention nowadays because of their use in applications that include display phosphors, security, imaging, therapy, solid state lasers, and optical amplifiers, in addition to several other applications 1- 3 . Among several luminescent materials, rare earth doped phosphors have found a big market in the photonics industry due to their synthesis flexibility, low cost of production, photo-stability, non-toxicity and size independent optical properties 4 . It should be noted that these superior properties make them competitors of organic dyes and quantum dots; both of which have several limitations 4 . It is anticipated that, especially in several biomedical and imaging applications, rare earth doped materials may soon replace organic dyes and quantum dots. The luminescence of trivalent rare earth ions arises from parity forbidden intra-configurational 4f→4f transitions. In making a highly emissive rare earth phosphor several dopant and host requirements have to be satisfied. While the dopant selections are made based on the absorption and emission wavelengths of interest, dopant concentration has to be set within the concentration quenching limit to overcome fluorescence quenching 5 . In addition, there are several host requirements such as low frequency vibrational groups, heavy metals, low level of impurities and water content 5 . When rare earths are bonded to high frequency vibrational groups such as carbon or hydroxyl groups, the long-lived excited states can be easily quenched by the presence of these high frequency vibrations and thereby reducing the quantum efficiency of the transition of interest 5 . It was found that halides and heavy metal combinations are the best materials for efficient luminescence due to their low vibration frequencies 5 . However, many of the halides are air sensitive as well as toxic and several of them could not find large scale industrial applications. Chalcogenides such as S, Se, Te etc. are also found to be potential candidates though the phonon frequency is little higher than halides 6 . Among Chalcogenides, rare earth oxysulfide possesses several excellent properties such as chemical stability, low toxicity and can be easily mass produced at low cost. It has average phonon energy of about 520 cm −1 7 . For example, Y 2 O 2 S: Yb, Er and Y 2 O 2 S: Er are two best mass produced commercial Green Photonics Award Light-Emitting Diodes: Materials, Devices, and Applications for Solid State Lighting XVI, edited by Klaus P. Streubel, Heonsu Jeon, Li-Wei Tu, Norbert Linder, Proc. of SPIE Vol. 8278, 82780E · © 2012 SPIE · CCC code: 0277-786X/12/$18 · doi: 10.1117/12.906804 Proc. of SPIE Vol. 8278 82780E-1 Downloaded from SPIE Digital Library on 07 Feb 2012 to 129.115.2.41. Terms of Use: http://spiedl.org/terms