Very high third-order nonlinear optical activities of intrazeolite PbS quantum dots

Zeolite-intercalated semiconductor quantum dots (QDs) have long been proposed to give very high third-order nonlinear optical (3NLO) responses. However, measurements of their 3NLO responses have not been possible due to the lack of methods to prepare optically transparent QD-incorporating zeolite films supported on optically transparent substrates and to confine QDs only within zeolite interiors. We found that the zeolite-Y films grown on indium-tin-oxide-coated glass plates (Ygs) remain firmly bonded to the substrates during ion exchange with Pb2+ ions, drying, and formation of PbS QDs by treating Pb2+ ions with H2S. A series of Ygs encapsulating different numbers (n = 0, 8, 14, 23, and 33) of PbS in a unit cell [(PbS)n-Yg] were prepared. The PbS QDs were expelled by adsorbed moisture to the external surfaces, and the expelled QDs formed large QDs. Coating of the (PbS)n-Ygs with octadecyltrimethoxysilane results in effective confinement of the QDs within the internal pores. The zeolite-encapsulated PbS QDs showed remarkably high 3NLO activities at 532 and 1064 nm which are unparalleled by other PbS QDs dispersed in other matrixes.