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

Abstract

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 °C) compared to the standard solid-state method (∼1300 °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 (∼4.5 eV) than that of the nominally pure matrix (∼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.