Optical memory and multistep luminescence thermochromism in single crystals of K2Na[Ag(CN)2]3

Single crystals of the layered compound K2Na[Ag(CN)2]3 exhibit a dual emission with high-energy (HE) and low-energy (LE) phosphorescence bands at 313 and 402 nm, respectively. Remarkably, the crystals exhibit "optical memory", in which a new emission band with intermediate energy (IE) at 380 nm is generated upon laser irradiation (lambda ex = 266 nm) at cryogenic temperatures. The irradiated crystals reinstate their original luminescence spectrum upon heating to room temperature and then recooling. In addition to these unusual "write/read/erase" changes, the crystals also exhibit multistep luminescence thermochromism such that the LE/HE intensity ratio increases between 17 and 80 K but then decreases upon further heating. The unprecedented occurrence of both novel phenomena in one compound has been related to reversible photophysical changes instead of irreversible photochemical changes.