Noah J.J. Johnson, Sha He, Shou Diao, Emory M. Chan, Hongjie Dai, and Adah Almutairi

Skaggs School of Pharmacy and Pharmaceutical Sciences and ‡Department of NanoEngineering, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093, United States

Department of Chemistry, Stanford University, Stanford, California 94305, United States

The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States

Publication Date: February 7, 2017

Abstract

Luminescence quenching at high dopant concentrations generally limits the dopant concentration to less than 1–5 mol% in lanthanide-doped materials, and this remains a major obstacle in designing materials with enhanced efficiency/brightness. In this work, we provide direct evidence that the major quenching process at high dopant concentrations is the energy migration to the surface (i.e., surface quenching) as opposed to the common misconception of cross-relaxation between dopant ions. We show that after an inert epitaxial shell growth, erbium (Er3+) concentrations as high as 100 mol% in NaY(Er)F4/NaLuF4 core/shell nanocrystals enhance the emission intensity of both upconversion and downshifted luminescence across different excitation wavelengths (980, 800, and 658 nm), with negligible concentration quenching effects. Our results highlight the strong coupling of concentration and surface quenching effects in colloidal lanthanide-doped nanocrystals, and that inert epitaxial shell growth can overcome concentration quenching. These fundamental insights into the photophysical processes in heavily doped nanocrystals will give rise to enhanced properties not previously thought possible with compositions optimized in bulk.