Luminescent Au ₁₁ nanocluster superlattices with high thermal stability

The poor thermal stability of nanoparticle superlattices heavily inhibits their practical applications. In present research, using stable thiolate-capped Au ₁₁(SCH ₂CH ₂COO ^-) ₇([CH ₃(CH ₂) ₇] ₄N ⁺) ₇ nanoclusters as the building blocks, novel luminescent Au ₁₁ nanocluster superlattices with high thermal stability have been fabricated by self-assembly. The nanocluster superlattices have a blade-like morphology and extend on a micrometre length scale with the largest over 50 μm. Under an excitation at 400 nm, the fabricated Au ₁₁ nanocluster superlattices emit a blue luminescence with the emission peak of 473 nm. The native stability of thiolate-capped gold nanoclusters and the steric repulsion induced by the high-density ligands (SCH ₂CH ₂COO ^-) ₇([CH ₃(CH ₂) ₇] ₄N ⁺) ₇ endows the fabricated superlattices with high thermal stability. The differential scanning calorimetry and thermogravimetric analysis indicates that the superlattices undergo irreversible endothermic transitions in the range of room temperature to 200 °C, which starts at 124 °C and reaches a peak at 160 °C. When processed with heat treatment below the transition temperature or stored for six months at room temperature, there is no obvious difference detected in the emission intensity of the fabricated Au ₁₁ nanocluster superlattices. Such thermostability gives the fabricated nanocluster superlattices great potential for many applications, especially for optical devices.