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Issue 28, 2015
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Deep red emission in Eu2+-activated Sr4(PO4)2O phosphors for blue-pumped white LEDs

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Abstract

The deep red phosphor Sr4(PO4)2O:Eu2+, which has an excitation peak around 450 nm for blue LED applications, is reported. This behavior is unusual for most phosphate phosphors. The crystal structure of Sr4(PO4)2O:Eu2+ is found to be monoclinic P21 and isotypic with Ca4(PO4)2O:Eu2+, which also shows deep red emission. Sr4(PO4)2O:Eu2+ has a larger lattice volume than Ca4(PO4)2O:Eu2+, but their emission and excitation spectra at room temperature are very similar. The key factors are discussed for achieving a large redshift of the 5d levels of Eu2+ ion in order to emit red light. In particular, the importance of the anion polarizability and the distortions of the metal coordination polyhedra are discussed, including the effective coordination number. Importantly, Sr4(PO4)2O:Eu2+ lacks the yellow emission at 77 K, which is found in Ca4(PO4)2O:Eu2+. The differences in thermal quenching behavior for Eu2+ dopants in Sr4(PO4)2O:Eu2+ and Ca4(PO4)2O:Eu2+ are attributed to the degree of auto/photo-ionization due to differences in the band gaps of these compounds. The importance of the large band gap of the host lattice in avoiding non-radiative processes of energy relaxation was confirmed.

Graphical abstract: Deep red emission in Eu2+-activated Sr4(PO4)2O phosphors for blue-pumped white LEDs

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Article information


Submitted
23 Apr 2015
Accepted
17 Jun 2015
First published
24 Jun 2015

J. Mater. Chem. C, 2015,3, 7356-7362
Article type
Paper
Author version available

Deep red emission in Eu2+-activated Sr4(PO4)2O phosphors for blue-pumped white LEDs

N. Komuro, M. Mikami, P. J. Saines, K. Akimoto and A. K. Cheetham, J. Mater. Chem. C, 2015, 3, 7356
DOI: 10.1039/C5TC01151E

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