Tunable red/ blue emitting of Ca5(PO4)3F: Eu2+, Eu3+ and remote-excited color convertor for NUV-WLED

Abstract

Eu2+/Eu3+ co-doped Ca5(PO4)3F (FAP) phosphors with tunable color of red/blue (R/B) emission were successfully synthesized by the two-step method for potential applications in light-emitting diodes (LED). Eu2+ (or Eu3+) single-doped and Eu2+/Eu3+ co-doped FAP all showed pure hexagonal FAP crystal with space group P63/m, indicating the occupation of Ca sites by Eu2+ and Eu3+ ions. Typically, Ca5(PO4)3F: Eu2+ phosphors exhibited a broad blue emission band at 451 nm under 293 nm excitation and Ca5(PO4)3F: Eu3+ samples emitted strong orange-red light at 596 nm, 615 nm and 620 nm under 394 nm excitation. Further, Eu2+/Eu3+ co-doped FAP phosphors obtained by the two-step method depicted the blue emission at 451 nm (Eu2+ ions) and the orange-red emission (Eu3+ ions) at 596 nm, 615 nm and 620 nm with an excitation wavelength of 365 nm (NUV). The tunable R/B ratio from 0.079 to 7.035 with various CIE chromaticity coordinate can be achieved by adjusting the recalcined temperature in the second step. Ca5(PO4)3F: Eu2+, Eu3+ sample can be packaged with green Lu3Al5O12 (LuAG) phosphors by 365 nm chip (1 W) and the cold white light with CIE chromaticity coordinate (0.2815, 0.3485) (CRI: 73, CCT: 7973 K) is achieving. Based on Ca5(PO4)3F: Eu2+, Eu3+ and 25B2O3-10SiO2-35ZnO-6Li2O-12La2O3-12WO3 (BS-glass) (in mol%) with strong mechanical strength as a great binder, the remote-excited color convertor (PiG: phosphor in glass) has been fabricated by screen printing technology for NUV-WLED application. Finally, by comparing the working temperature of PiG and pc-WLED at the same operating time, the working temperature of PiG was stable at 32 °C when remote excitation lighting was applied, which greatly avoided the phenomenon of “thermal quenching” for phosphors caused by high temperature under the operating of WLED. Thus, it was demonstrated that Eu2+ and Eu3+ co-doped Ca5(PO4)3F phosphors with tunable red/blue emitting would be a highly potential candidate for NUV-WLED.