Engineering Ligand–Metal Charge Transfer States in Cross-Linked Gold Nanoclusters for Greener Luminescent Solar Concentrators with Solid-State Quantum Yields Exceeding 50% and Low Reabsorption Losses

Luminescent solar concentrators (LSCs) can be used to concentrate direct and diffused sunlight, which are crucial ingredients for photovoltaic windows. Recently, efficient LSCs based on heavy-metal colloidal quantum dots (CQDs) have been demonstrated by designing their heterostructures. Eco-friendly thoilate-stabilized gold nanoclusters (AuNCs) with ligand–metal charge transfer states might be greener alternatives for large-Stokes-shift luminophores in LSCs. Unfortunately, low photoluminescence quantum yields (PL-QYs) and poor understanding of the PL mechanism significantly hinder their practical utilities. Here, the photophysical properties were investigated for Zn2+-induced cross-linked AuNCs (Zn–AuNCs) dissolved in solution and embedded in a rigid solid matrix. We found that the Zn–AuNCs at pH 4 exhibit enhanced PL-QYs of 7.7% and enlarged Stokes shifts as compared with that of as-prepared AuNCs (PL-QY ≈ 0.4%). More importantly, Zn–AuNCs embedded in a rigid matrix hold extremely high solid-state PL-QYs up to ∼53% along with a blue-shifted PL spectrum because of the combined effects of the suppression of nonradiative relaxation and the switching of emissive triplet states. Motivated by these appealing photophysical properties, greener LSCs were fabricated, exhibiting negligible reabsorption losses and a high internal quantum efficiency of 34∼36%, which is already comparable with that of the LSCs based on toxic CQDs.