Yb-and Er concentration dependence of the upconversion luminescence of highly doped NaYF_(4):Yb,Er/NaYF_(4):Lu core/shell nanocrystals prepared by a water-free synthesis  

作　　者：Christian Würth Bettina Grauel Monika Pons Florian Frenzel Philipp Rissiek Kerstin Rücker Markus Haase Ute Resch-Genger 

机构地区：[1]Federal Institute for Materials Research and Testing(BAM),Division Biophotonics,Richard-Willstaetter-Str.11,12489 Berlin,Germany [2]Institut für Chemie Neuer Materialien,Fachbereich Biologie/Chemie,Universität Osnabrück,Barbarastraße 7,49076 Osnabrück,Germany

出　　处：《Nano Research》2022年第10期9639-9646,共8页纳米研究（英文版）

基　　金：the German Science Foundation DFG(grants RE 1203/18-1 and HA 1649/7-1);the EU(COST 1403)for financial support.

摘　　要：High sensitizer and activator concentrations have been increasingly examined to improve the performance of multi-color emissive upconversion(UC)nanocrystals(UCNC)like NaYF_(4):Yb,Er and first strategies were reported to reduce concentration quenching in highly doped UCNC.UC luminescence(UCL)is,however,controlled not only by dopant concentration,yet by an interplay of different parameters including size,crystal and shell quality,and excitation power density(P).Thus,identifying optimum dopant concentrations requires systematic studies of UCNC designed to minimize additional quenching pathways and quantitative spectroscopy.Here,we quantify the dopant concentration dependence of the UCL quantum yield(ΦUC)of solid NaYF_(4):Yb,Er/NaYF_(4):Lu upconversion core/shell nanocrystals of varying Yb3+and Er3+concentrations(Yb3+series:20%‒98%Yb3+;2%Er3+;Er3+series:60%Yb3+;2%‒40%Er3+).To circumvent other luminescence quenching processes,an elaborate synthesis yielding OH-free UCNC with recordΦUC of~9%and~25 nm core particles with a thick surface shell were used.High Yb3+concentrations barely reduceΦUC from~9%(20%Yb3+)to~7%(98%Yb3+)for an Er3+concentration of 2%,thereby allowing to strongly increase the particle absorption cross section and UCNC brightness.Although an increased Er3+concentration reducesΦUC from~7%(2%Er3+)to 1%(40%)for 60%Yb3+.Nevertheless,at very high P(>1 MW/cm^(2))used for microscopic studies,highly Er3+-doped UCNC display a high brightness because of reduced saturation.These findings underline the importance of synthesis control and will pave the road to many fundamental studies of UC materials.

关 键 词：highly doped upconversion nanocrystals core/shell nanoparticles upconversion luminescence efficiency NaYF_(4):Yb ER concentration quenching 

分 类 号：TB383.1[一般工业技术—材料科学与工程]