Insight into the crystal structure and photoluminescence properties of an extremely broadband yellow-emitting phosphor Sr8MgCe(PO4)7:Eu2+

Abstract

The combination of binary complementary color phosphors with near-ultraviolet (NUV) light-emitting diode (LED) chips was put forward to lower the energy loss caused by the reabsorption of the combination of tricolor phosphors with NUV LED chips. Thus investigating broadband yellow-emitting phosphors with enriched red components in the spectral range has gained much attention. Here, an extremely broadband yellow-emitting phosphor Sr₈MgCe(PO₄)₇:Eu²⁺ with sufficient red component in the spectral region was synthesized. Due to the introduction of Ce into the host, Sr₈MgCe(PO₄)₇ shows an emission band with a peak at 375 nm when excited at 310 nm. Meanwhile, Eu²⁺ doped Sr₈MgCe(PO₄)₇ exhibits an extremely broad yellow emission band with a full width at half-maximum of 175 nm and a peak located at about 598 nm, due to the 5d–4f transitions of Eu²⁺ ions substituting five Sr²⁺ sites. The excitation peak of the host at 310 nm was detected in the excitation spectrum of Sr₈MgCe(PO₄)₇:Eu²⁺ monitored at 598 nm, indicating the energy transfer from the host to Eu²⁺, which was also proved by the decay curves. On the other hand, the excitation band at about 400 nm due to the 4f–5d transitions of Eu²⁺ was also detected in the excitation spectrum of Sr₈MgCe(PO₄)₇:Eu²⁺, and this matches well with the NUV LED chips. Moreover, the energy transfer between Eu²⁺ ions at different crystallographic sites was demonstrated by time-resolved photoluminescence (TRPL) spectra. A white LED with a CRI (R_a) of 82.88 and a CCT of 4238 K was prepared through a 400 nm NUV LED chip, Sr₈MgCe(PO₄)₇:Eu²⁺ and BaMgAl₁₀O₁₇:Eu²⁺ (BAM:Eu²⁺). These results pave the way for designing better Eu²⁺-doped phosphors for NUV WLEDs with binary complementary color phosphors.