Multi-emission processes of hierarchically structured NaGdF:Tm:Yb:Tb core@shell nanoparticles

Hierarchically structured-lanthanide (Ln III )-doped β-NaGdF 4 nanoparticles emitting by upconversion (UC), downconversion (DC) and/or downshifting (DS) are currently investigated for potential applications as anti-counterfeiting agents or in energy conversion. Yet, the role of doping concentration, excitation pump power density ( P exc ), and Ln III -Ln III separation on the Ln III -to-Ln III energy transfer (ET), luminescence quenching, and emission color tunability need to be further elucidated to boost their luminescence. In light of that, herein, these issues are discussed in nanostructured β-NaGdF 4 :Tb III ,Tm III ,Yb III core@shell nanoparticles emitting by UC, DS, and DC. In the NaGd y − x Tm 0.015 Yb 0.20 Tb x F 4 @NaYF 4 compositions, larger Tb III amounts induce stronger Tb III UC while for P exc lower than 20 W cm −2 , both cooperative sensitization upconversion (CSU) and energy transfer upconversion (ETU) mechanisms may occur. On the other hand, for P exc larger than 50 W cm −2 , energy migration upconversion (EMU) dominates the UC. By separating Tb III from Tm III and Yb III in core@shell@NaGdF 4 architectures, only the CSU and ETU mechanisms occur, while for P exc densities larger than 40 W cm −2 , saturation of upconversion takes place. Upon 488 nm excitation, Tb III DS and Yb III DC emissions are noticed as well. Thus, this study helps to understand how the proper design of hierarchically structured nanoparticles can control the Ln III -to-Ln III ET mechanisms while their versatile excitation and multi-emission are interesting features for use as anti-counterfeiting agents or in energy conversion. Hierarchically structured-lanthanide-doped β-NaGdF 4 nanoparticles emitting by upconversion (UC), downconversion (DC) and/or downshifting (DS) have been investigated for potential applications as anti-counterfeiting agents or in energy conversion.