Stronger Reductive Environment in Solvothermal Synthesis Leads to Improved Ga Doping Efficiency in ZnO Nanocrystals and Enhanced Plasmonic Absorption

Abstract

The key parameter for degenerated semiconductor oxide plasmonic nanocrystals is the doping level. Hydrothermal and solvothermal approaches are considered to be less effective toward achieving high concentration of aliovalent donor dopants in a host oxide when compared to other synthesis methods that use long chain hydrocarbon solvents, fatty acids, and fatty amines as precursors. Because of this, although they have several advantages such as sustainability, ease of use, relatively inexpensive reagents and apparatus, and reduced environmental impact, they are excluded from the list of potential synthesis methods. Herein, an effective Zn 2þ substitution with aliovalent Ga 3þ in the ZnO host lattice is demonstrated, and it is achieved by increasing the reductive power of the solvothermal synthesis conditions by either solvent substitution or the addition of reducing agents. This increase results in an increased oxidation affinity of the medium. This in turn promotes Ga 3þ incorporation into the ZnO lattice, by skewing the reaction equilibrium toward oxygen evolution.

Permanent photodoping of plasmonic gallium-ZnO nanocrystals

“…To obtain higher electron concentrations and stronger plasmonic absorption, the nanocrystals have been synthesized in more reductive or oxygen poor conditions. 6,11 In the present study we show, that the plasmonic absorp-tion from itinerant electrons can be permanently increased by photodoping and that the added electrons remain stable even in ambient air. Photodoping is well reported in literature for various semiconductor materials including TiO2 12 and ZnO.…”

“…10 Various synthesis and preparation approaches have been used to ensure efficient doping. 6,10,11 Still, an effectively incorporated dopant does not guarantee the formation of a delocalized electron. For example, aliovalent donor dopants can be compensated (localised) by other point defects such as cation vacancies or oxygen interstitials.…”