Terbium-doped calcium germanate (Ca 2 GeO 4 ) as a potential candidate for LED application
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RESEARCH ARTICLE
Terbium-doped calcium germanate (Ca2GeO4) as a potential candidate for LED application I. Koseva1 • P. Tzvetkov1 • P. Ivanov2 • P. Petrova2 • R. Tomova2 A. Yordanova1 • V. Nikolov1,3
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Received: 6 February 2020 / Accepted: 13 July 2020 Ó The Optical Society of India 2020
Abstract Powder samples of Ca2GeO4 doped with 0.5, 1, 2 and 3 at.% Tb3? were prepared via solid-state synthesis technique. The obtaining of pure phase at all dopant concentrations was proved through XRD analyses. In the emission and excitation spectra of the obtained powders, the characteristic peaks of Tb3? ion were observed. The Tb3? excitation spectrum in the range from 300 to 500 nm shows characteristic transitions of Tb3?, attributed to the f– f transitions. The strongest peak is located at 379 nm corresponding to the 7F6 ? 5D3 transition. The main emission peak of Tb3? is 5D4 ? 7F5 transitions at 545 nm, corresponding to green color. Other transitions are located at 416 (5D3 ? 7F5), 437 (5D3 ? 7F4), 458 (5D3 ? 7F3), 488 (5D4 ? 7F6), 588 (5D4 ? 7F4), 621 (5D4 ? 7F3), 651 (5D4 ? 7F2) and 675 (5D4 ? 7F1) nm. The optimum emission is observed for 2 at.% Tb3? ion concentration. At this concentration dominate also (5D4 ? 7F4) and (5D4 ? 7F3) transitions. CIE coordinates of the samples show different emission colors depending on the active ion concentration. The obtained results confirm that as-prepared terbium-doped materials could be used like green, yellow and reddish phosphors.
& R. Tomova [email protected] 1
Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
2
Institute of Optical Materials and Technologies ‘‘Acad. J. Malinowski’’, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
3
Institute of Mineralogy and Crystallography, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
Keywords Germanate phosphor Ceramic materials for LED Rare-earth ions X-ray Photoluminescence
Introduction Light-emitting diodes as environmentally friendly energy and efficient solid-state light sources become more widely used in modern life. It is expected that LEDs may replace traditional light bulbs and tubes because of their long lifetime, durability and much higher degree of freedom to tune the light emission spectrum compared to conventional lighting technologies [1]. The commercial LEDs are realized by combining blue, green and red light-emitting phosphors, and thus, the obtained color can be controlled. Unfortunately, this method displays different drawbacks [2, 3]. As the rare-earth ions have different energy levels and possess different emission colors, they are suitable for active ions for preparing luminescent materials. The luminescence of the rare-earth activated compounds depends on the composition of the host, concentration of the activator and methods of preparation [3]. Chemical and physical stable materials with strong absorption in the UV region and high conversion efficiency are of importance for inorganic light-emitting diodes [2, 4]. Oxide materials with their ther
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