Pb²⁺ Ions Doping Induced Cooperative Luminescence Quenching of Yb³⁺-trimers in CaF₂

At room temperature, the ultraviolet (UV) upconversion emissions from CaF₂: Pb²⁺, Yb³⁺ were observed under the excitation of 978 nm near infrared (NIR) laser. The upconversion emission peak is centered at 383 nm, which is ascribed to the ³P₀ → ¹A_1g (¹S₀) transition of Pb²⁺ ions. Through the results of transient measurements, the upconversion process of Pb²⁺ ions is confirmed. The energy transfer process is that three excited Yb³⁺ ions simultaneously transfer their energy to one Pb²⁺ ion. With the increasing of Pb²⁺ concentration, the cooperative luminescence from Yb³⁺ clusters decreases gradually. In order to explain this phenomenon, we propose a new cooperative luminescence quenching mechanism in this paper, which is originated from Pb²⁺ induced structure destruction of Yb³⁺-trimers. The fluorescence quenching in Pb²⁺ and Yb³⁺ codoped CaF₂ is given a reasonable explanation.