Investigation on optical properties of borate Sr3Y2B4O12: Ce/Tb/Sm and its application in wLEDs

Abstract

Several series of near-ultraviolet (n-UV) convertible white Ce/Tb/Sm-tridoped borate Sr3Y2B4O12 (SYBO) via Ce → Tb → Sm energy transfer (ET) have been successfully obtained by solid-state reaction under reducing atmosphere. The reason why picks Ce/Tb/Sm ions is based on the facts that these lanthanide ions are all extensively used ions in inorganic phosphors and emitting typically in blue, green and red region, respectively, that could be easily mixed and regulated to obtain warm white light within a single phase matrix. The structure, determined from XRD and analysed based on the Rietveld method, shows Y and Sr have 8-fold and 10-, 9- and 8-fold coordination, respectively, and all dopants are more inclined to enter Y sites as compared with Sr sites due to different degrees of radius ratio and charge among the dopants, Y and Sr. The ET mechanism is detailed studied via photoluminescence and decay lifetimes, where the obvious spectral overlap of the PLE for Tb/Sm and PL of Ce with systematic relatively decrease and increase of PL peaks of Ce, Tb/Sm, respectively, clearly indicate the ET occurs. Further, according to spectral studies on codoped (Ce/Tb, Ce/Sm and Tb/Sm) and tridoped phosphors, the Tb acts actually as the ET bridge to better connect Ce and Sm due to ET directly from Ce to Sm is difficult to achieve. Finally, the near-ideal white light from optimal SYBO:Ce/Tb/Sm with color coordinates of (x = 0.328, y = 0.343) and Ra = 86 was observed under n-UV excitation indicates this kind of phosphors could be potentially applied in solid-state lighting.