The self-reduction ability of RE3+ in orthosilicate (RE = Eu, Tm, Yb, Sm): BaZnSiO4-based phosphors prepared in air and its luminescence

• The phosphor BaZnSiO4: Eu2+/Tm2+/Yb2+ can be prepared in air.
• The self-reduction of RE3+ to RE2+ result from the defect chemistry at Ba2+ sites.
• BaZnSiO4 can stabilize low-valence ions is due to its three-dimensional network.
• The white-emitting phosphor BaZnSiO4:0.03Eu show a superior synthesis route.

Nominal composition phosphors BaZnSiO4:RE (RE = Eu, Tm, Sm, Yb) were synthesized by the conventional solid-state method in air (oxidizing atmosphere, OA) and under 10%H2/90%N2 flow (reductive atmosphere, RA) conditions, respectively. Self-reduction phenomenon, which is a valence change from trivalent rare-earth ions (RE3+) to corresponding divalent state (RE2+) without reducing agent, were observed in the samples of Eu/Tm/Yb-doped BaZnSiO4 but have not observed in Sm-doped samples. Compared with RA condition, the ca. percent of the reductive concentration of Eu2+/Tm2+/Yb2+ in the phosphors BaZnSiO4 prepared in OA condition are 21%, 15% and 35%, respectively. It was found that both of BaZnSiO4:Eu and BaZnSiO4:Tm prepared in air show greatly broad band emission peak at 500 nm under the excitation of ultraviolet (UV), which indicated they are potential phosphors for UV-based LED. The factors which are related to self-reduction degree have been also discussed. The successful synthesis of BaZnSiO4:RE2+/3+ phosphors in air provides a new route to obtain other novel orthosilicate-based materials.

The self-reduction ability of RE (RE = Eu/Tm/Yb/Sm) in BaZnSiO4-based phosphors prepared in air was compared and explained. The white-emitting of BaZnSiO4:0.03Eu prepared in oxidizing atmosphere shows a potential environmentally friendly route to obtain phosphor for UV-based LED.Figure optionsDownload as PowerPoint slide