Speaker
Mr
Simon Nnalue Ogugua
(University of the Free State)
Description
Effects of annealing on luminescent properties of mixed lanthanum oxyorthosilicates co-doped Dy3+ and Pr3+ phosphors.
Simon N. Ogugua1, Hendrik C. Swart1, Odireleng M. Ntwaeaborwa2
1 Department of Physics, University of the Free State, Bloemfontein, ZA9300, South Africa.
2School of Physics, University of the Witwatersrand, Private Bag 3, Wits, 2050, South Africa.
For the past three decades, phosphors have made an impressive contribution to technological development for various applications including, solid-state lighting, solar cells, theft prevention, optical amplifiers, optical lasers, medicine, etc. We have investigated photoluminescent and cathodoluminescent properties of mixed lanthanum oxyorthosilicates co-doped with dysprosium (Dy3+) and praseodymium (Pr3+). When co-doped with Dy3+; Pr3+either act as a sensitizer or excitation energy absorber depending on the host material. Pr ions can exist in the trivalent (Pr3+) or tetravalent (Pr4+) state, but only the Pr3+ ions are optically active, while the Pr4+ ions are luminescence quenchers. Hence, it is important to reduce the amount of Pr4+ ions in any luminescence material to improve intensity of emitted light. We have prepared single and mixed host lanthanum yttrium oxyorthosilicates (La2-xYxSiO5, x = 0, 0.5, 1, 1.5 and 2) co-doped Dy3+ and Pr3+ powder phosphors using solution combustion synthesis. The materials were annealed at 950 °C in air and 5% H2 (in Ar) gas to reduce the oxygen vacancies and excess Pr4+ to Pr3+, respectively. The diffuse reflectance data showed an absorption peak around 376 nm, attributed to the O2-→Pr4+ charge transfer band. Both the band gap and luminescence properties of the samples were enhanced after annealing in 5% H2 (in Ar). This suggests that the amount of Pr4+ in the samples decreased as confirmed from the X-ray photoelectron spectroscopy results. The luminescence (PL and CL) showed evidence of energy transfer from Pr3+ to Dy3+ in some of the samples. The CIE coordinates of the samples (both PL and CL) showed tunable colour that was influenced by annealing atmospheres and La to Y ratio.
Supervisor details<br><b>If not a student, type N/A.</b><br>Student abstract submision<br>requires supervisor permission:<br>please give their name,<br> institution and email address.
Prof. O.M. Ntwaeaborwa,WITS,odireleng.ntwaeaborwa@wits.ac.za
Prof. H.C. Swart, UFS, SwartHC@ufs.ac.za
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Primary author
Mr
Simon Nnalue Ogugua
(University of the Free State)
Co-authors
Prof.
Hendrik Swart
(University of the Free State, Bloemfontein)
Prof.
Odireleng Martin Ntwaeaborwa
(School of Physics University of the Witwatersrand Johannesburg)
