The photophysics of ionic semiconductors at low temperatures: Silver bromide, silver iodide, and cuprous oxide

Three ionic semiconductors that differ in the character of their lowest energy transitions were examined. Silver bromide (AgBr) has an indirect gap, silver iodide (AgI) a direct gap, and cuprous oxide (Cu{dollar}sb2{dollar}O) a direct but parity forbidden lowest energy transition. Donor-acceptor (D-A) pair recombination was identified in the three materials using time-resolved spectroscopy and the decay dynamics were compared to a previously developed theoretical model. Nanocrystals of each material were synthesized and the effects of quantum confinement on the low temperature recombination dynamics were studied.; The dynamics of the emission from aqueous prepared nanocrystals of AgBr was compared to that of larger crystals. The observed lifetime of the free exciton increased from {dollar}sim{dollar}20 {dollar}mu{dollar}s to {dollar}sim{dollar}600 {dollar}mu{dollar}s as the size of the crystallite decreased from 41 to 8 nm. The D-A pair recombination kinetics were bulk-like in 41 nm AgBr while in the 8 nm samples the decay lasted longer. Factorial experiments led to methods of synthesis of nanocrystals in aqueous solvents allowing the dying of the nanocrystals. Preliminary spectroscopic evidence indicated J-aggregates of pseudoisocyanine (PIC) dye were adsorbed to the nanocrystal surface.; Tabular AgI nanocrystals exhibiting one dimensional confinement were synthesized. The D-A nature of the broad luminescence observed in emission from AgI has been confirmed. The D-A emission decay rates for 0.5 {dollar}mu{dollar}m and 52 nm crystals were indistinguishable. Quantum confinement effects are manifest in a blue shift of the emission and a loss of the longer lived decay components in {dollar}sim{dollar}5 nm thick tabular AgI nanocrystals. Measurements of the rise time and decay time of exciton luminescence using photoluminescence upconversion were attempted.; Microcrystals and nanocrystals of Cu{dollar}sb2{dollar}O were synthesized via aqueous methods with the intention of completing previous quantum confinement studies where severely heat treated purchased Cu{dollar}sb2{dollar}O was compared to aqueous prepared poly(vinyl alcohol) size restricted material. The broad emission around 640 nm observed in photoluminescence from Cu{dollar}sb2{dollar}O has been identified as donor-acceptor recombination and the effects of size restriction on the emission dynamics have been examined.