Ensemble and single particle studies of the excitation power density (P)-dependent upconversion luminescence (UCL) of core and core-shell β-NaYF_(4):Yb,Er upconversion nanoparticles (UCNPs) doped with 20% Yb^(3+) and...Ensemble and single particle studies of the excitation power density (P)-dependent upconversion luminescence (UCL) of core and core-shell β-NaYF_(4):Yb,Er upconversion nanoparticles (UCNPs) doped with 20% Yb^(3+) and 1% or 3% Er^(^(3+)) performed over a P regime of 6 orders of magnitude reveal an increasing contribution of the emission from high energy Er^(3+) levels at P > 1 kW/cm^(2). This changes the overall emission color from initially green over yellow to white. While initially the green and with increasing P the red emission dominate in ensemble measurements at P < 1 kW/cm^(2), the increasing population of higher Er^(^(3+)) energy levels by multiphotonic processes at higher P in single particle studies results in a multitude of emission bands in the ultraviolet/visible/near infrared (UV/vis/NIR) accompanied by a decreased contribution of the red luminescence. Based upon a thorough analysis of the P-dependence of UCL, the emission bands activated at high P were grouped and assigned to 2–3, 3–4, and 4 photonic processes involving energy transfer (ET), excited-state absorption (ESA), cross-relaxation (CR), back energy transfer (BET), and non-radiative relaxation processes (nRP). This underlines the P-tunability of UCNP brightness and color and highlights the potential of P-dependent measurements for mechanistic studies required to manifest the population pathways of the different Er^(3+) levels.展开更多
Oxygen sensing,magnetic,and upconversion luminescence properties are combined in multi-functional composite particles prepared herein by a simple mixing,baking,and grinding procedure.Upconverting nanocrystals are used...Oxygen sensing,magnetic,and upconversion luminescence properties are combined in multi-functional composite particles prepared herein by a simple mixing,baking,and grinding procedure.Upconverting nanocrystals are used as an excitation source and an oxygen indicator with far-red emission.The composite particles are excited with near infrared(NIR)laser light(980 nm).The visible upconversion emission is converted into an oxygen concentration-dependent far-red emission(<750 nm)using an inert mediator dye and a platinated benzoporphyrin dye.This concept combines the advantages of NIR excitation and far-red emissive indicator dyes,offering minimized auto-fluorescence and enhanced membrane permeability.Additional functionality is obtained by incorporating magnetic nanoparticles into the composite particles,which enables easy manipulation and separation of the particles by the application of an external magnetic field.展开更多
基金The authors thank the European Upconversion Network(EUN)for financial support of a research exchange program(COST-CM1403)U.R.-G.,F.F.and C.W.acknowledge financial support by research grants RE 1203/20-1(project NANOHYPE,DFG and M-Eranet).Y.M.is grateful to the Institut Universitaire de France(IUF)for support and providing additional time to be dedicated to research.
文摘Ensemble and single particle studies of the excitation power density (P)-dependent upconversion luminescence (UCL) of core and core-shell β-NaYF_(4):Yb,Er upconversion nanoparticles (UCNPs) doped with 20% Yb^(3+) and 1% or 3% Er^(^(3+)) performed over a P regime of 6 orders of magnitude reveal an increasing contribution of the emission from high energy Er^(3+) levels at P > 1 kW/cm^(2). This changes the overall emission color from initially green over yellow to white. While initially the green and with increasing P the red emission dominate in ensemble measurements at P < 1 kW/cm^(2), the increasing population of higher Er^(^(3+)) energy levels by multiphotonic processes at higher P in single particle studies results in a multitude of emission bands in the ultraviolet/visible/near infrared (UV/vis/NIR) accompanied by a decreased contribution of the red luminescence. Based upon a thorough analysis of the P-dependence of UCL, the emission bands activated at high P were grouped and assigned to 2–3, 3–4, and 4 photonic processes involving energy transfer (ET), excited-state absorption (ESA), cross-relaxation (CR), back energy transfer (BET), and non-radiative relaxation processes (nRP). This underlines the P-tunability of UCNP brightness and color and highlights the potential of P-dependent measurements for mechanistic studies required to manifest the population pathways of the different Er^(3+) levels.
基金This research was funded by Austrian Science Fund(FWF,I 442-N19)Deutsche Forschungsgemeinschaft(DFG,WO 669/12-1),both within the framework of an ERA Chemistry project.
文摘Oxygen sensing,magnetic,and upconversion luminescence properties are combined in multi-functional composite particles prepared herein by a simple mixing,baking,and grinding procedure.Upconverting nanocrystals are used as an excitation source and an oxygen indicator with far-red emission.The composite particles are excited with near infrared(NIR)laser light(980 nm).The visible upconversion emission is converted into an oxygen concentration-dependent far-red emission(<750 nm)using an inert mediator dye and a platinated benzoporphyrin dye.This concept combines the advantages of NIR excitation and far-red emissive indicator dyes,offering minimized auto-fluorescence and enhanced membrane permeability.Additional functionality is obtained by incorporating magnetic nanoparticles into the composite particles,which enables easy manipulation and separation of the particles by the application of an external magnetic field.
