The correlation between the structural and luminescent properties of Ca2SiO4:Eu2+ nanopowders prepared by the sol-gel...

Ca2SiO4:Eu2+ powders were prepared by the sol-gel process using calcium nitrate hydrate, europium nitrate hydrate, and tetraethyl orthosilicate (TEOS). The effects of the amount of TEOS, firing temperatures, and the Eu2+ concentration on the structural and luminescence properties were investigated. The CaO impurity phase was produced and it strongly contributed to emission properties. The prepared powders were composed of irregular-shaped particles, square plates (CaO), and/or needle-shaped particles, depending on the amount of TEOS, while with excess TEOS content (1.2 M), Ca2SiO4:Eu2+ crystals were contained in the glass matrix. The photoluminescence excitation (PLE) spectra of the synthesized powders widely covered from 250 to 450 nm. The related PL emission spectra showed green emissions (- 510 nm), which resulted from two overlapped Gaussian emission bands centered at 502 and 550 nm assigned to the 4f(7)-4f(6)5d1 transitions of the Eu(II) and Eu(I) sites, respectively. Eu2+ ions were incorporated into CaO as well as Ca2SiO4, and thus the Eu2+ concentration in Ca2SiO4 was adjusted by the amount of the CaO phase in samples. As a result, the strongest green emission of Ca2SiO4:Eu2+ was obtained with 0.9 M TEOS.