Yb- and Er concentration dependence of the upconversion luminescence of highly doped NaYF4:Yb,Er/NaYF4:Lu core/shell nanocrystals prepared by a water-free synthesis

Abstract 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 first strategies were reported reduce concentration quenching in highly doped UCNC. UC luminescence (UCL) is, however, controlled not only by dopant concentration, yet an interplay different parameters including size, crystal shell quality, excitation power density ( P ). Thus, identifying optimum requires systematic studies UCNC designed minimize additional pathways quantitative spectroscopy. Here, we quantify dependence UCL quantum yield ? ) solid :Yb,Er/NaYF :Lu core/shell varying Yb 3+ Er (Yb series: 20%–98% ; 2% 60% 2%–40% To circumvent other processes, elaborate synthesis yielding OH-free with record ?9% ?25 nm core particles a thick surface used. barely from (20% ?7% (98% for 2%, thereby allowing strongly increase particle absorption cross section brightness. Although increased reduces (2% 1% (40%) . Nevertheless, at very high (> 1 MW/cm 2 used microscopic studies, -doped display brightness because reduced saturation. These findings underline importance control will pave road many fundamental materials.