resumo
Novel red emitting KCaBO3:Eu phosphors have been synthesized by solid-state reaction at various temperatures. Systematic studies on annealing effects and consequent structural evolution and optical properties were investigated by various structural and photoluminescence studies. With an increase in annealing temperature (from 700 degrees C to 950 degrees C), these phosphors show a gradual change from a mixed low crystalline phase to a highly crystalline single phase, with minimized volatile impurities. Photoluminescence studies revealed that the low-temperature annealed phosphors showed distinct mixed emission composed of blue and red emissions upon UV excitation. Such dual emission is due to the coexistence of Eu3+ and Eu2+ ions, wherein the reduction of Eu3+ into Eu2+ was attributed to the presence of volatile impurities. Relatively high-temperature annealed phosphors exhibit strong red color photoluminescence due to homogeneously occupied Eu3+ ions in the host crystal charge-compensated (with K+ ions) sites of Ca2+ ions. The dominant red-to-orange emission intensity ratios and Judd-Ofelt parameters of Eu3+ ions support the strong covalent nature and site-occupation of higher asymmetry sites of K+ and Ca2+ ions. High emission life times and efficient and stable photoluminescence at different excitation wavelengths make these phosphors suitable for white LEDs and other display applications.
palavras-chave
RARE-EARTH IONS; LIGHT-EMITTING-DIODES; LUMINESCENCE PROPERTIES; ENERGY-TRANSFER; BORATE GLASSES; RE2+ RE; EU3+; EMISSION; SPECTROSCOPY; EU2+
categoria
Chemistry
autores
Reddy, AA; Das, S; Ahmad, S; Babu, SS; Ferreira, JMF; Prakash, GV
nossos autores
Allu Amarnath Reddy
Estudante de doutoramento
José Maria da Fonte Ferreira
Professor(a) Jubilado(a)agradecimentos
The authors acknowledge the financial support from Department of Information Technology (DIT), Govt. of India, under Photonics Development Program (ref. 12(1)/2008-PDD). This is part of the High-Impact Research Scheme of IIT Delhi. The authors are highly thankful to Prof. Jeremy Baumberg, Cavendish Laboratory, University of Cambridge, UK for allowing us to record PL mapping studies. The support from CICECO, University of Aveiro is also acknowledged.