Energy Migration Up-conversion of Tb³⁺ in Yb³⁺ and Nd³⁺ Codoped Active-Core/Active-Shell Colloidal Nanoparticles

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