Assembly-Induced Enhancement of Cu Nanoclusters Luminescence with Mechanochromic Property

Abstract

Metal nanoclusters (NCs) as a new class of phosphors have attracted a great deal of interest owing to their unique electronic structure and subsequently molecule-like optical properties. However, limited successes have been achieved in producing the NCs with excellent luminescent performance. In this paper, we demonstrate the significant luminescence intensity enhancement of 1-dodecanethiol (DT)-capped Cu NCs via self-assembly strategy. By forming compact and ordered assemblies, the original nonluminescent Cu NCs exhibit strong emission. The flexibility of self-assembly allows to further control the polymorphism of Cu NCs assemblies, and hence the emission properties. Comparative structural and optical analysis of the polymorphic NCs assemblies permits to establish a relationship between the compactness of assemblies and the emission. First, high compactness reinforces the cuprophilic Cu(I)···Cu(I) interaction of inter- and intra-NCs, and meanwhile, suppresses intramolecular vibration and rotation of the capping ligand of DT, thus enhancing the emission intensity of Cu NCs. Second, as to the emission energy that depends on the distance of Cu(I)···Cu(I), the improved compactness increases average Cu(I)···Cu(I) distance by inducing additional inter-NCs cuprophilic interaction, and therewith leads to the blue shift of NCs emission. Attributing to the assembly mediated structural polymorphism, the NCs assemblies exhibit distinct mechanochromic and thermochromic luminescent properties. Metal NCs-based white light-emitting diodes are further fabricated by employing the NCs assemblies with blue-green, yellow, and red emissions as phosphors.

All‐Copper Nanocluster Based Down‐Conversion White Light‐Emitting Devices

“…WLEDs were fabricated by integrating blue and orange emitting Cu NC powders on a commercial GaN LED chip providing 370 nm excitation emission, and show favorable white light characteristics with Commission Internationale de l'Eclairage (CIE) color coordinates, CRI, and CCT of (0.36, 0.31), 92, and 4163 K, respectively. Compared with previously reported metal NC based LEDs,9, 12 a warmer white light with higher CRI is demonstrated here.…”

“…This issue can be overcome by using an additional suitable red emitting rare‐earth phosphor; however, their typically small Stokes shifts lead to a strong reabsorption of emitted light, resulting in the decrease of efficiency and color stability 5, 7. This triggered an ongoing search for alternative, rare‐earth free phosphors for WLEDs 8, 9. Among them, metal nanoclusters (NCs)9, 10 are attractive, as they can be easily synthesized in solution, processed into powders, and, for the noble metal NCs, exhibit strong PL with a large Stokes shift 11.…”

“…This triggered an ongoing search for alternative, rare‐earth free phosphors for WLEDs 8, 9. Among them, metal nanoclusters (NCs)9, 10 are attractive, as they can be easily synthesized in solution, processed into powders, and, for the noble metal NCs, exhibit strong PL with a large Stokes shift 11. Copper is an earth abundant element widely used in different industries, and there have been few reports on down‐conversion WLEDs with Cu NCs as phosphors, mostly in combination with other luminophores 9.…”

“…Among them, metal nanoclusters (NCs)9, 10 are attractive, as they can be easily synthesized in solution, processed into powders, and, for the noble metal NCs, exhibit strong PL with a large Stokes shift 11. Copper is an earth abundant element widely used in different industries, and there have been few reports on down‐conversion WLEDs with Cu NCs as phosphors, mostly in combination with other luminophores 9. Yang and co‐workers reported WLEDs employing a combination of blue‐green emitting Cu ribbons (PL QY of 6.5%), yellow emitting Cu nanosheets (PL QY of 3.6%), and red emitting Au nanosheets, self‐assembled from Cu and Au NCs 9.…”

“…Copper is an earth abundant element widely used in different industries, and there have been few reports on down‐conversion WLEDs with Cu NCs as phosphors, mostly in combination with other luminophores 9. Yang and co‐workers reported WLEDs employing a combination of blue‐green emitting Cu ribbons (PL QY of 6.5%), yellow emitting Cu nanosheets (PL QY of 3.6%), and red emitting Au nanosheets, self‐assembled from Cu and Au NCs 9. Along a similar concept, Liu et al fabricated WLEDs employing blue‐green emitting Cu sheets (PL QY of 4.6%) and red emitting Au sheets obtained by electrophoretic deposition of Cu and Au NCs 12.…”