Synthesis and surface modification of amino-stabilized CdSe, CdTe and InP nanocrystals

CdSe, CdTe and InP nanocrystals were prepared by an organometallic synthesis using mixtures of highly boiling primary amines and trioctylphosphine (TOP) as the coordinating solvent, and were characterized by powder XRD, SAXS, HRTEM, absorption and luminescence spectroscopy. The use of amines allowed us to obtain small crystalline nanoparticles for all materials investigated. In all cases, as-prepared colloids show rather narrow particle size distributions which can be further improved by standard size selective precipitation. Amino-capped II–VI nanocrystals show strong size-dependent band edge photoluminescence (PL). CdSe nanocrystals with the mean particle size in the range of 1.2–3.0 nm exhibit emission from blue to green with room temperature quantum yields of 15–20%. CdTe nanocrystals (2.5–5.0 nm size range) show a PL tunable from green to red with quantum yields up to 65% at room temperature. InP nanocrystals (1.5–4.0 nm size range) possess a weak emission (<1% quantum efficiency (QE)). A simple method is proposed to transfer nanocrystals from organic solvents to water which allows to retain sufficiently strong luminescence of CdTe nanoparticles. CdSe nanocrystals synthesized in trioctylphosphine–trioctylphosphine oxide mixture (TOP–TOPO) show an increased QE of about 70% after subsequent treatment with primary amines.