We report a colloidal synthesis of alkyl-passivated germanium (Ge) nanocrystals with widely tunable size. Average diameters range from 3 to 18 nm and the nanocrystals exhibit band edge near infrared (NIR) photoluminescence (PL). The synthesis involves the heating-up of GeI2 in a mixture of oleylamine (OLAm) and octadecene (ODE). Nanocrystal growth proceeds by two sequential mechanistic steps at low and then high temperature. First, OLAm promotes the decomposition of GeI2 to Ge at relatively low temperature to lead to nanocrystal nucleation and growth. OLAm also serves as a capping ligand. Its reversible bonding to Ge allows nanocrystals to grow in this low temperature range. Growth then terminates when the temperature becomes hot enough to induce hydrogermylation of ODE. OLAm ligands are displaced by a layer of covalently bonded alkyl groups. The nanocrystal size is tuned by adjusting the reactant concentrations and heating rate. The largest nanocrystals (&gt;11 nm) are obtained by adding trioctylphosphine (TOP) to further modify the GeI2 decomposition rate. The optical properties of these Ge nanocrystals quantum dots are compared to two-dimensional Ge nanosheet structures with organic ligand passivation.

Colloidal synthesis of germanium nanocrystal quantum dots with size-tunable near-infrared photoluminescence

ACS Spring Meeting 2021

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