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

Abstract

A series of CaSiO _3 : x %Tb ^3+ , y %Sm ^3+ 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 Tb ^3+ and Sm ^3+ doped compounds consists of a series of peaks corresponding to electronic transitions of Tb ^3+ and Sm ^3+ ions. The wavelength of 375 nm was optimal to excite the luminescence of Tb ^3+ /Sm ^3+ 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 Tb ^3+ electronic transitions of ^5 D _3 → ^7 F _5 , ^5 D _3 → ^7 F _4 , ^5 D _3 → ^7 F _3 , ^5 D _4 → ^7 F _6 , ^5 D _4 → ^7 F _5 , ^5 D _4 → ^7 F _4 , and ^5 D _4 → ^7 F _3 , respectively. The PL emission spectrum of the Sm ^3+ 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 Sm ^3+ from ^4 G _5/2 to ^6 H _5/2 , ^6 H _7/2 , and ^6 H _9/2 , 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.

Keywords

• photoluminescence
• phosphors
• white-LED
• color coordinates
• color temperature
• color rendering index