Study on luminescent properties of Tb3+ and Sm3+ co-doped CaSiO3 phosphors for white light emitting diodes

Abstract

A series of CaSiO3:x%Tb3+, y%Sm3+ compounds was synthesized by the conventional solid state reaction. X-ray diffraction, scanning electron microscopy, and energy dispersive x-ray spectroscopy investigations were conducted to determine crystal structure. The photoluminescence (PL) excitation spectrum of Tb3+ and Sm3+ doped compounds consists of a series of peaks corresponding to electronic transitions of Tb3+ and Sm3+ions. The wavelength of 375 nm was optimal to excite the luminescence of Tb3+/Sm3+ co-doped compounds. The PL emission spectrum consists of a set of intense lines at wavelengths of 415 nm, 436 nm, 457 nm, 488 nm, 543 nm, 586 nm, and 622 nm, corresponding to Tb3+ electronic transitions of 5D3 → 7F5, 5D3 → 7F4, 5D3 → 7F3, 5D4 → 7F6, 5D4 → 7F5, 5D4 → 7F4, and 5D4 → 7F3, respectively. The PL emission spectrum of the Sm3+ doped compound has a series of three peaks located at wavelengths of 565 nm, 602 nm, and 648 nm, corresponding to the electronic transitions of Sm3+ from 4G5/2 to 6H5/2, 6H7/2, and 6H9/2, respectively. The energy level diagram was proposed. The lifetime measurements were conducted for all samples and energy transfer process was also examined by this way. The Commission Internationale de I’Eclairage chromaticity coordinates, correlated color temperature, and color rendering index of phosphors were determined and the results indicate that the obtained materials are optimal candidate for white LED applications.