Temperature-induced exciton switching in long alkyl chain based inorganic-organic hybrids

Photoluminescence and transmission is systematically explored in thin films of long–alkyl-chain-based inorganic-organic (IO) hybrids (CnH2n+1NH3)2PbI4 (n = 12, 16, 18) (CnPI) and NH3C12H22NH3PbI4 (DDPI). Such IO-hybrids, which form natural multiple quantum well structures stacked up along c-axis, possess strong room-temperature exciton transitions. These hybrids exhibit reversible phase transition of two different crystal phase transitions at easily accessible device temperatures. Flipping the structural phase is clearly reflected in switching of the excitons with corresponding photoluminescence and transmission changes showing clear thermal hysteresis. The phase-dependent switching of excitons is predominantly due to reversible crumpling of the inorganic PbI sheet networks. Systematic temperature dependent studies establish a correlation between the structure and optical exciton features. Such thermo-optic exciton switching suggests possible new photonic devices.