Mengfei Zhang

Highly efficient Sr3Y2(Si3O9)2:Ce3+,Tb3+/Mn2+/Eu2+ phosphors for white LEDs: structure refinement, color tuning and energy transfer

A series of highly efficient and emission-tunable Sr3Y2(Si3O9)2(SYSO):Ce3+,Tb3+/Mn2+/Eu2+ phosphors have been prepared via a solid-state reaction. The structure refinement indicates that the as-prepared phosphors crystallized in a monoclinic phase with a space group of C2/c (no. 15), and there are three kinds of cation sites in the host lattice for the doped ions to occupy. The Ce3+ emission at different lattice sites in the SYSO host has been firstly identified and discussed. When introducing other doping ions into these cation sites, there exist efficient energy transfers from Ce3+ ions to these doping ions (Tb3+, Mn2+, and Eu2+) under UV excitation. The corresponding energy transfer mechanisms from Ce3+ to Tb3+/Mn2+/Eu2+ in SYSO:Ce3+,Tb3+/Mn2+/Eu2+ systems have been studied systematically. These energy transfers not only can enhance the luminescent efficiencies and broaden the width of emission spectra of SYSO:Ce3+,Tb3+/Mn2+/Eu2+ phosphors but also can modulate their emission colors from blue to green, orange or cyan, respectively. For example, the maximum quantum yields (QYs) of as-prepared SYSO:0.15Ce3+,xTb3+/yMn2+ phosphors can reach 90.4% and 74% at x = 0.70, y = 0.01, respectively. Based on these experiment results, the as-prepared SYSO:Ce3+,Tb3+/Mn2+/Eu2+ phosphors can act as potential color-tunable and emission band-widened phosphors for possible applications in ultraviolet light based white LEDs.

Size-tunable synthesis and luminescent properties of Gd(OH)3:Eu3+ and Gd2O3:Eu3+ hexagonal nano-/microprisms

Uniform and monodisperse Gd(OH)3:Eu3+ hexagonal prisms were successfully synthesized at mild conditions via a large-scale and facile homogeneous coprecipitation process without using any catalysts, surfactants or templates. The size of the as-formed Gd(OH)3:Eu3+ precursor prisms could be modulated from the micro- to nanoscale by the use of urea and changing the pH values of the initial solutions. A possible formation mechanism for the Gd(OH)3:Eu3+ hexagonal nano-/microprisms was proposed. After a postannealing process, Gd2O3:Eu3+ hexagonal nano-/microprism phosphors with a slight shrinking in size can be transformed from Gd(OH)3:Eu3+. Both the Gd2O3:Eu3+ nanoprisms and microprisms exhibit the same strong red emission corresponding to the 5D0 → 7F2 transition (610 nm) of Eu3+ under UV light excitation (243 nm) and low-voltage electron beam excitation (1–6 kV). Furthermore, the experimental results indicate that the luminescence properties of the as-obtained phosphors are dependent on their morphologies and sizes. As a result of the controllable morphology and size, and excellent luminescence properties, these Gd2O3:Eu3+ nano-/microprism phosphors may find potential applications in optoelectronic devices (fluorescent lamps and field emission displays), bioanalysis and biomedical areas and so on.