Tunable color emitting of Ba1-x-ySiO3:xEu,yBi3+ phosphors with the self-reduction of Eu3+ ions calcined in air

A series of Ba1-xSiO3:xEu and Ba0.92-ySiO3:0.08Eu, yBi3+ phosphors have been synthesized using one-step calcination of a precursor prepared by chemical co-precipitation. The self-reduction phenomenon of Eu3+ is observed and verified by photoluminescence (PL), excitation (PLE) spectra and X-ray photoelectron spectroscopy (XPS). Under 353 nm excitation, the Ba1-x-ySiO3:xEu,yBi3+ phosphors exhibit a broad band ranging from 390 nm to 560 nm with a peak centered at 499 nm originating from the 4f65d→4f7 transition of Eu2+ ions and several narrow band emissions peaked at 464 nm, 537 nm, 581 nm, 590 nm, 615 nm, 660 nm and 705 nm can be attributed to 5D2→7F0, 5D1→7F1, 5D0→7F0, 5D0→7F1, 5D0→7F2, 5D0→7F3 and 5D0→7F4 transition of Eu3+, respectively. The self-reduction of Eu3+→Eu2+ in BaSiO3:Eu calcined in air has been explained from the following aspects: the charge compensation mechanism and the structures of 3-D networks composed by SiO4 tetrahedra, helpful for maintaining of the reduction (Eu3+→Eu2+) at a high temperature. Co-doping Bi3+ ions can both enhance the emissions from Eu2+ and Eu3+ because the doped Bi3+ ions not only can make vacancy for Eu2+ but also can enhance the emitting for Eu3+ in BaSiO3. Moreover, when excited by 370 nm, the CIE chromaticity coordinates of Ba0.92SiO3:0.08Eu and Ba0.912SiO3:0.08Eu,0.008Bi3+ are (0.3521, 0.3141) and (0.3558, 0.3408), meanwhile their correlated color temperature (CCT) are 4478 K and 4523 K, which belongs to the warm white light region. Furthermore, the decay curves are measured and can be well fitted with double exponential decay equation. It shows that both the average lifetimes of Eu2+ and Eu3+ are extended with the concentration of Bi3+ ions increasing. Therefore, the Ba1-x-ySiO3:xEu,yBi3+ phosphor is a promising warm white‐light emitting diodes (w-LEDs) integrated with NUV chips.