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 Tb 3+ ions with the Yb 3+ and Nd 3+ sensitizers at 980 and 808 nm photoexcitation, respectively. The [Nd 3+ → Yb 3+ ]→ [Yb 3+ → Tb 3+ ] EMU phenomenon was significantly enhanced by spatial displacement of the sensitizing Nd 3+ ions from the activator Tb 3+ ions by intentionally introducing an intermediate Yb 3+ sensitizer layer forming a [Nd 3+ → Yb 3+ ] → [Yb 3+ ] → [Yb 3+ → Tb 3+ ] system. Otherwise Tb 3+ emission was considerably quenched by Nd 3+ ions even though they were spitted between the core and shell, respectively. Moreover, (Tb 3+,Yb 3+ ) → (Tb 4+,Yb 2+ ) valence change has been discovered to limit the Tb 3+ 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.