Analog metal-to-nonmetal exciton transition: Effect of isotopic alloying on naphthalene triplet transport

A low-temperature investigation of the rate of triplet exciton transport within the guest (${\mathrm{C}}_{10}$ ${\mathrm{H}}_8$) quasilattice of the ${\mathrm{C}}_{10}$ ${\mathrm{D}}_8$-${\mathrm{C}}_{10}$ ${\mathrm{H}}_8$ crystal system has demonstrated a transition from bandlike to hoppinglike motion upon reduction of the guest-to-host concentration ratio. The analog metal and nonmetal regimes are characterized, respectively, by a negative and a positive transport temperature coefficient. In addition, reducing the naphthalene concentration by a factor of 5 reduces the transport rate by five orders of magnitude.