Journal
OPTICAL MATERIALS
Volume 76, Issue -, Pages 125-140Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.optmat.2017.12.032
Keywords
Phosphors; Photoluminescence; Oxyorthosilicates; X-ray photoelectron spectroscopy
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Funding
- African Laser Center (ALC), Department of Science and Technology, the competitive programme for rated researchers (CPRR) of the National Research Foundation (NRF)-South Africa [CPR20110724000021870]
- rental pool programme of the National Laser Center (NLC) [NLC-LREGM]
- South African Research Chairs Initiative of the Department of Science and Technology
- National Research Foundation of South Africa [84415]
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The effect of post-annealing atmospheres (air and Ar-H-2) on the optical properties of La2-xYxSiO5 (x = 0, 0.5, 1, 1.5 and 2) co-doped Pr-0.25(3+) and Dy-0.25(3+) powder phosphors were studied. The X-ray diffraction patterns showed that the as-prepared samples have higher full width at half maximum (FWHM) than the annealed samples. The elemental composition, oxidation states, and chemical and electronic states of the phosphors were determined using the X-ray photoelectron spectroscopy. The band gap values determined from the diffuse reflectance spectra were shown to increase following the post-annealing treatments (with the values increasing in the following manner: Ar-H-2-annealed > air-annealed > as prepared). The photoluminescence intensities of the phosphors also followed the same trend as the band gap values. Two different cases of the photoluminescence mechanisms were proposed for the La2-xYxSiO5:Pr-0.25(3+),0.25DY3+ phosphors. Case 1: The 4f5d energy level of Pr3+ lies within the band gap of the host and energy transfer was observed from Pr3+ to Dy3+ via the overlapping 4f5d emission peak of PO+ and the I-4(15/2) excitation peak of Dy3+. Case II: The 4f5d energy level of Pr3+ lies close or inside the conduction band of the host and the energy transfer was not observed from Pr3+ to Dy3+. The CIE colour coordinates of the phosphors showed tunable emission colours (blue, red and white). (C) 2017 Elsevier B.V. All rights reserved.
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