Interface disorder in large single- and multi-shell upconverting nanocrystals

Abstract

The growth of core–shell nanocrystals (NCs) can lead to extended interface disorder due to the intermixing of core and shell materials. Such an issue is particularly important for large single- and multi-shell upconverting NCs, which have been considered as being relatively insusceptible to intermixing. In this work, a robust methodology – based on structure-independent local chemical analyses with nanometer-scale resolution and high-energy synchrotron X-ray powder diffraction – has been used to shed new light on the chemical and structural organization of large single-, double-, and triple-shell upconverting NCs. The experimental results reveal, for the first time, that significant disorder: (i) exists at the interfaces of large (20–50 nm) multi-shell upconverting NCs; (ii) reaches core–shell and shell–shell interfaces, independently of their position within the structure; (iii) can be partially controlled by the shell deposition method; and (iv) leads to the formation of multiple length-scale interfaces depending on the size of the starting seeds, the number and relative thickness of the pre-existing shells in the seeds. It is anticipated that the results will be beneficial in furthering the fundamental understanding of the structure–property relationships of multi-shell upconverting NCs.