Ca(上标 2+)掺杂对BaMgSiO4: Eu(上标 2+)发光材料发光性能的影响

The Eu(superscript 2+)-doped silicate based phosphors are very suitable for LEDs. These phosphors show broad emission colors which may vary from near UV to red light through 4f-5d transition of Eu(superscript 2+) activator and strongly depend on the host lattice, thus the emission wavelength is tunable by modifying the composition and structure of the hosts. This provides a possible way to fabricate color-tunable phosphors for LEDs. In this article, a new composition of color-tunable phosphor material Ba(subscript 1-x)Ca(subscript x)MgSiO4: Eu(superscript 2+) doped with Ca(superscript 2+) (x≤0.15) was synthesized by conventional solid-state reaction in a reductive atmosphere (95% N2 + 5% H2), their luminescent properties and the influence of Ca(superscript 2+) content were investigated by X-ray diffraction (XRD) and fluorescence spectrometer. The results showed that the emission of the phosphors turns from 498 to 450 nm, when the content of Ca(superscript 2+) increases in 0~0.05. The maximum emission and excitation intensity are reached when the content of Ca(superscript 2+) is equals to 0.075, and the shape of the excitation spectra also changes as increasing the content of Ca(superscript 2+). The XRD curves show that the single phase limit of Ca(superscript 2+) in the phosphors is below 0.075. The results can be explained by Ca(superscript 2+) substitution for Ba(superscript 2+) in different lattice sites and the crystal field strength. As reported by Mingying Peng et al in the structure of BaMgSiO4, there are three different barium sites Ba(1), Ba(2) and Ba(3) with equal amounts in the lattice. The 498 nm emission band corresponds to the Eu(superscript 2+) emission on the Ba(1) and Ba(2) sites. And the two absorption bands at 360 and 400 nm in the excitation spectrum are assigned to the Eu(superscript 2+) centers on Ba(1) and Ba(2) sites, respectively. The Ba(superscript 2+) at the Ba(2) can be more easily substituted by Ca(superscript 2+) because of a longer average Ba-O distances [Ba(1):0.289 nm; Ba(2):0.294 nm; Ba(3):0.274 nm]. The strength of crystal field around the Eu(superscript 2+) ion on Ba(1) sites changes when Ca(superscript 2+) substitutes the Ba(superscript 2+) at Ba(2), which leads to the change of excitation and emission spectra of the Eu(superscript 2+) ion on Ba(1) sites. Then, when the content of Ca(superscript 2+) is over 0.075, Ca(superscript 2+) at Ba(2) reaches saturation, and the CaMgSiO4 phase occurs. This leads to impurity quenching. Ca(superscript 2+) substitution for Ba(superscript 2+) at Ba(1) also causes the change of the excitation spectrum.