Luminescent Studies of “Exciplex Tuning” for Nanoclusters of Dicyanocuprate(I) Ions Doped in Potassium Chloride Crystals

Abstract

Nanoclusters of dicyanocuprate (I) ions doped in potassium chloride crystals have been studied. Several emission bands are observed in this system and each emission band can be tuned by site-selective spectroscopy. These bands are assigned to different [Cu(CN)2]− luminescent nanoclusters in the host lattice. The Cu+ ions substitute for K+ ions in the lattice and the CN− ions substitute for Cl− ions in the host with dimer and trimer nanoclusters bonded together by CN− bridges. This is unlike KAg(CN)2 or KAu(CN)2 substituted in a KCl lattice, in which Ag−Ag or Au−Au bonding directly occurs. Ab initio calculations show that the LUMO is a bonding MO while the HOMO is antibonding. Extended Hückel calculations indicate the formation of the LUMO excited-state well is deeper than the ground-state HOMO potential well and with a shorter internuclear separation characteristic of exciplex behavior. Time-resolved luminescence measuremence at room temperature and 78 K demonstrate that, upon pulsed excitation, energy transfer occurs between the dimer and trimer nanoclusters. We conclude that the presence of different luminescent Cu(CN)2− nanoclusters in different environments results in tunability over a wide wavelength range.