Microwave-assisted solvothermal synthesis of Eu3+-doped CsY2F7 and RbY2F7 phosphorescent nanoparticles.

We synthesized Eu3+-doped CsY 2 F 7 and RbY 2 F 7 nanoparticles (orthorhombic crystal structure, Pnna space group, No. 52) by the microwave-assisted solvothermal technique and investigated the influence of reaction temperature and fluoride ion concentration on the particles' phase and crystal structure. Fluoride ions were added in excess of the stoichiometric amount to achieve the orthorhombic phase for C s Y 2 F 7 and to convert the cubic RbY 3 F 10 to the orthorhombic RbY 2 F 7. Mild synthesis conditions yielded nanoparticles with crystallites ranging in size from 19 to 37 nm and a combination of spherical, rod-like, and hexagonal shapes. Nanoparticles emit a strong orange and red light when excited into the Eu3+5L 6 level, which is centered around 390 nm. The strongest emission peak is around 612 nm, which comes from the 5D 0 →7F 2 electronic transitions. Emission intensity dependence on Eu3+ concentration revealed that nanoparticles can be heavily doped with Eu3+, up to 25 % with respect to Y3+. Emission decay measurements provided values of excited state lifetimes of 6.2 ms for the Cs(Y 0.75 Eu 0.25) 2 F 7 and 6.0 ms for the Rb(Y 0.75 Eu 0.25) 2 F 7. [ABSTRACT FROM AUTHOR]