Cooperative Energy Transfer between Two Neighboring Eu³⁺ Ions and Energy Transfers from Eu²⁺ to Eu³⁺ and from Eu³⁺ to Yb³⁺ in Crystals for Quantum Cutting

Energy transfer between Eu2+ and Eu3+ ions is examined in CaF2 crystal at not only room temperature but also 12 K. Energy transfer from Eu2+ to Eu3+ is confirmed. The reverse energy transfer from Eu3+ to Eu2+, however, is confirmed to be undetectable. Cooperative energy transfer between two neighboring Eu3+ ions in Eu3+-doped LiYb1-xEux(MoO4)(2) crystal, which is combined with Eu-O charge transfer complex resonantly, is found to be responsible for the 1000 nm near infrared broadband emission from Yb3+ ions through the quantum cutting from the D-5(2) excited state of Eu3+.