H F Lin
Articles written in Bulletin of Materials Science
Volume 38 Issue 7 December 2015 pp 1867-1873
A series of red phosphors Ca1−2𝑥WO4 : 𝑥Eu3+, 𝑥Li+ (𝑥 = 0.01, 0.02, 0.04, 0.06, 0.12, 0.20 and 0.30) in pure phase were synthesized via high-temperature solid-state reaction and their luminescent properties were investigated. For comparison, the 6 mol% Eu3+-doped CaWO4 was also obtained and investigated. The crystal structures of these phosphors were characterized by powder X-ray diffraction, and the luminescent properties of Eu3+-, Li+-codoped CaWO4 were investigated by diffuse reflectance spectra, photoluminescence emission spectra, photoluminescence excitation spectra, and the Commission International de L' Eclairage (CIE) chromaticity indexes. These spectra illustrated that Eu3+-, Li+-codoped CaWO4 phosphors could effectively be excited by a 270 nm ultraviolet (UV) or 394 nm near UV chip, and exhibit red emission originated from the 5D0 $\rightarrow$ 7F𝐽 (𝐽 = 1 and 2) transitions of Eu3+. The fluorescent intensities of red emission band centred at 610 nm of 6 mol% Eu3+-, Li+-codoped CaWO4 were about 1.27 times stronger than that of 6 mol% Eu3+-doped CaWO4 under 394 nm excitation. The 12 mol% doping concentration of Eu3+ ions in CaWO4 is optimum when excited at 394 nm, while excited at 270 nm the sample with 6 mol% was the best one. The concentration quenching mechanism could be attributed to the dipole–dipole interaction between the Eu3+ ions. The CIE colour coordinates can be tuned from yellowish red to deep red with varying concentrations of Eu3+. The present work suggests that Eu3+-, Li+-codoped CaWO4 as red phosphors exhibit great potential application in the near UV excited white-light-emitting diode.
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