Red phosphor based on Eu3+-isoelectronically doped Ba2SiO4 obtained via sol-gel route for solid state lightning

The present paper reports on the effect of Eu3+ concentration (1-5%, considering a charge compensation mechanism) on the structural, morphological and spectroscopic properties of Ba2SiO4 produced by using a novel approach that involves an adapted sol-gel route. XRD data showed that high crystalline and single phase doped Ba2SiO4 samples were prepared at lower calcination temperature (1100 degrees C) compared to the standard solid-state method (similar to 1300 degrees C). FTIR, Raman and DRS analyses indicated that the Ba2+ replacement by Eu3+ ions causes punctual structural defects in the Ba2SiO4 lattice, which particles observed by SEM imaging have irregular shape characteristics for the use of the acid-catalyzed sol-gel method. Optical bandgap values evaluated by DRS measurements of the red phosphors are smaller (similar to 4.5 eV) than that of the nominally pure matrix (similar to 5.8 eV), evidencing that Eu3+ ions increase Ba2SiO4 structural/electronic defects. The detailed analysis of the f-f Eu3+ narrow transitions in the photoluminescence spectra showed that doping ions occupy at least two non-equivalent sites without an inversion center in the Ba2SiO4 host. Moreover, the 5% doped sample also exhibited a third Eu3+ anomalous site assigned to the Eu3+-O2- associates, which has a spectral behavior distinct from Eu3+ occupying ordinary host lattice sites. Finally, the 4%-doped sample exhibited the highest relative emission intensity while the 5%-doped, the highest quantum efficiency (72.6%) which qualifies these materials as potential candidates to be used as red phosphors for solid state lightning. (AU)