Unraveling the Eu2+ → Mn2+ Energy Transfer Mechanism in w‑LED Phosphors

• Published in: Journal of physical chemistry. C 2020-06, Vol.124 (25), p.13902-13911
• Main Authors: Sontakke, Atul D, van Bunningen, Arnoldus J, Rabouw, Freddy T, Meijers, Sam, Meijerink, Andries
• Format: Article
• Language: English
• Subjects: C: Plasmonics; Optical, Magnetic, and Hybrid Materials
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.0c03425

Recent research on white light LED (w-LED) phosphors has focused on narrow-band green and red luminescent materials to improve the efficacy of w-LEDs and to widen the color gamut of w-LED-based displays. Mn2+ is a promising emitter capable of narrow-band emission, either green or red, depending on the local coordination. However, the extremely low absorption coefficients for the spin- and parity-forbidden d–d transitions in Mn2+ form a serious drawback and require addition of a sensitizer ion such as Ce3+ or Eu2+, with strong absorption in the blue. The performance of the codoped phosphor then critically depends on efficient energy transfer. Despite extensive research, a clear understanding of the Eu2+→ Mn2+ and Ce3+→ Mn2+ transfer mechanism is lacking. Typically, Dexter exchange interaction or electric dipole–quadrupole coupling are considered. Here we investigate Eu2+→ Mn2+ energy transfer in Ba2MgSi2O7 and show that the most probable mechanism is exchange interaction with fast (nanoseconds) energy transfer from Eu2+ to nearest-neighbor Mn2+ and much slower (>100 ns) transfer to next-nearest neighbors, as expected for exchange interaction. We critically evaluate previous studies where the assignment of dipole–quadrupole interaction was erroneously based on C Mn 8/3 concentration dependence of energy transfer efficiencies. Preferential Eu2+–Mn2+ pair formation is suggested as a mechanism that enhances energy transfer efficiencies.