Article pubs.acs.org/JPCC
Wide-Band Excited YTiTaO6: Eu3+/Er3+ Phosphors: Structure Refinement, Luminescence Properties, and Energy Transfer Mechanisms Yang Zhang,†,‡ Dongling Geng,†,‡ Xuejiao Li,†,‡ Jian Fan,†,‡ Kai Li,†,‡ Hongzhou Lian,† Mengmeng Shang,*,† and Jun Lin*,† †
State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, People’s Republic of China ‡ University of the Chinese Academy of Sciences, Beijing 100049, People’s Republic of China S Supporting Information *
ABSTRACT: Eu3+-/Er3+-activated YTiTaO6 phosphors have been prepared via conventional solid state reaction process. X-ray diffraction (XRD) and structure refinement, Raman spectra, X-ray photoelectron Spectrum (XPS), photoluminescence (PL) spectra, cathodoluminescence (CL) spectra, and lifetimes were utilized to characterize the synthesized samples. Under UV light excitation, the YTiTaO6 sample shows broad band emission centered near 505 nm due to the Ta(Ti)O6 polyhedron. Eu3+ and Er3+ ions doped YTiTaO6 samples show strong line emissions coming from the characteristic f−f transitions. The energy transfer from the Ta(Ti)O6 group of the host to Eu3+ and Er3+ in YTiTaO6 phosphors has been demonstrated to be a resonant type via a dipole−dipole mechanism, and the critical distance (RC) for host emission to Eu3+ and Er3+ calculated by concentration quenching method are 10.02 and 18.86 Å, respectively. Under the low voltage electron beam excitation, the CL spectra of YTiTaO6, YTiTaO6: Eu3+, and YTiTaO6: Er3+ samples are similar to their PL spectra, exhibiting bluish-green, red, and green luminescence, respectively, which indicates that these materials might be promising for application in solid-state lighting and field-emission displays.
1. INTRODUCTION
Generally speaking, most of the phosphors are based on an optically silent host lattice into which a small amount of activator ions are doped. These activators have excitation energy levels that can be excitated by direct excitation or by energy transfer from the host, and then emissions from the excitation states are subsequently observed.28−30 Due to the abundant emission colors based on their 4f−4f or 5d−4f transitions, rare-earth ions have frequently been chosen as activators.31−36 In particular, the Eu3+ ions, as one of the most widely used red emitting activators, mainly show characteristic emissions resulting from the transitions of 5D0,1,2−7FJ (J = 4, ..., 0). Er3+-doped phosphors have been widely applied as greenemitting materials based on 2H11/2, 4S3/2-−I15/2 transitions of Er3+ ions.37−40
Recently, the development of inorganic luminescent materials has attracted a fast growing interest due to their indispensable applications in lighting (e.g., fluorescent tubes and white lightemitting diodes), displays (e.g., cathode ray tubes, field emission displays and vacuum fluorescent displays), and imaging (X-ray imaging scintillators), etc.1−12 Due to their fascinating merits such as energy savings, high brightness, being environmentally friendly, and having a long lifetime, white light-emitting diodes (WLEDs) have aroused another revolution in illumination to overtake conventional incandescent or fluorescence lamps.13−19 Moreover, in the display field, field emission displays (FEDs) have been considered as the next generation flat-panel displays due to their potential to provide displays with thin panels, wide viewing, quick response times, high brightness, self-emission, and a high contrast ratio.20,21 Thus, searching for highly efficient phosphors has been a hot topic for material scientists.22−27 © 2014 American Chemical Society
Received: May 6, 2014 Revised: June 18, 2014 Published: July 8, 2014 17983
dx.doi.org/10.1021/jp504437f | J. Phys. Chem. C 2014, 118, 17983−17991
The Journal of Physical Chemistry C
Article
YTiTaO6, as a special group of materials with A3+B4+C5+O6 combination, has attracted considerable attention for their microwave properties.41 In this compound, Y3+ ions occupy Cxy S (4) sites coordinated by 6-fold oxygen to form an irregular YO69− polyhedron, and Ta5+ and Ti4+ ions occupy C1(8) sites coordinated by 6-fold oxygen randomly distributed on the same crystallographic positions in the framework, respectively.42 Actually, because of the promising chemical characteristics and optical properties, YTiTaO6 can be used as host for efficient luminescence.41,43 Thus, in this work, we present a luminescent material with the general composition of YTiTaO6: Eu3+/Er3+, which can be excitated by UV light and a low voltage electron beam. Besides the crystallographic sites occupation, CIE coordinates and energy transfer mechanism have been studied in detail. It is found that they have potential application in lighting and display fields.
2. EXPERIMENTAL SECTION 2.1. Materials. The initial rare-earth oxides, including Y2O3 (99.999%), Eu2O3 (99.999%), and Er2O3 (99.999%), were purchased from Science and Technology Parent Company of Changchun Institute of Applied Chemistry, TiO2, Nb2O5, and Ta2O5 were purchased from Beijing Chemical Company. All chemicals were used directly without further purification. 2.2. Preparation. A series of YTiTaO6: Eu3+/Er3+ powder samples were prepared by a conventional solid state reaction process. Typically, the stoichiometry amounts of Y2O3, TiO2, and Ta2O5 with a purity higher than 99.99% were mixed in an agate mortar by adding ethanol and then adequately triturated for a good mixing. The dried powders were obtained after baking in an oven at 80 °C for 30 min. Then the mixtures were calcined at 1400−1500 °C for 10 h. 2.3. Characterization. The X-ray diffraction (XRD) patterns were performed on a D8 Focus diffractometer at a scanning rate of 10° min−1 in the 2θ range from 20° to 100° with graphite-monochromatized Cu Kα radiation (λ = 0.15405 nm). The structure refinement was done using the General Structure Analysis System (GSAS) program.44 The photoluminescence (PL) measurements were recorded with a Hitachi F-7000 spectrophotometer equipped with a 150 W xenon lamp as the excitation source. Raman spectrum was collected using a micro-Raman spectrometer (Renishaw) with a laser of 532 nm wavelength. XPS spectra were measured with a Thermo ESCALAB 250 instrument. The cathodoluminescence (CL) measurements were conducted in an ultrahigh-vacuum chamber (
