Energy Migration Up-conversion of Tb³⁺ in\nYb³⁺ and Nd³⁺ Codoped Active-Core/Active-Shell\nColloidal Nanoparticles

Abstract

The intentional design of chemical\narchitecture of lanthanide doped\nluminescent nanoparticles through the proper selection of dopants\nin core–shell and core–shell–shell structures\nenables optimization of their optical properties. Such an approach\nallows one to achieve energy transfer up-conversion (ETU) and energy\nmigration mediated up-conversion (EMU) and green emission from Tb³⁺ ions with the Yb³⁺ and Nd³⁺ sensitizers\nat 980 and 808 nm photoexcitation, respectively. The [Nd³⁺ → Yb³⁺]→ [Yb³⁺ → Tb³⁺] EMU phenomenon was significantly enhanced by spatial displacement\nof the sensitizing Nd³⁺ ions from the activator Tb³⁺ ions by intentionally introducing an intermediate Yb³⁺ sensitizer layer forming a [Nd³⁺ → Yb³⁺] → [Yb³⁺] → [Yb³⁺ →\nTb³⁺] system. Otherwise Tb³⁺ emission was considerably\nquenched by Nd³⁺ ions even though they were spitted between\nthe core and shell, respectively. Moreover, (Tb³⁺,Yb³⁺) → (Tb⁴⁺,Yb²⁺) valence change\nhas been discovered to limit the Tb³⁺ up-conversion emission.\nThe studies explain how the chemical architecture of the smartly designed\nactive-core @ active-shell luminescent nanoparticles may improve their\nspectral properties.