Preparation And Optical Properties Of PbS Quantum Dots Doped Oxide Glass-ceramics

Quantum dots?QDs?are one kind of quasi-zero-dimensional semiconductor nanocrystals.Owing to quantum confinement effect,QDs have size-dependent optical properties,and thus have potential applications in many fields ranging from chemical sensing and biomedicine through to light-emitting diodes and photovoltaics.Compared to II–VI and III–V QDs,lead chalcogenide QDs have large Bohr exciton radii with a strong quantum confinement and narrow bandgap energies,resulting in a wide tunable spectral range from visible to even mid-infrared region by varying their size.Although colloidal lead chalcogenide QDs have been successfully synthesized by solution-based approach,precipitation of QDs in inorganic glasses through heat-treatment method is continuously pursued,because of their promising potential in photonic devices.However,due to the large surface to volume ratio of quantum dots,photoluminescence properties of lead chalcogenide QDs were strongly influenced by the defects on the surface of QDs.These surface defects act as traps for charge carriers,seriously reducing the luminescence efficiency through non-radiative recombination in surface traps or deep trap emissions on the low-energy side of the band-edge emissions.For chemical synthesized colloidal QDs,surface defects can be passivated by organic ligands or by forming a crystalline shell on the top of core QDs.However,such methods are rather challenging to be applied when QDs were precipitated in the glass,since it is quite hard to assemble the desired nanostructures in solid matrix.One to modify the local environment of QDs by growing another crystal on QDs or precipitating QDs in glass-ceramics might be a likely way to partially passivate the surface defects of QDs.Given this,the study and research on the precipitation of PbS QDs doped glass containing sodium strontium silicate?Na₂SrSi₂O₆?nanocrystals and strontium silicate?SrSiO₃?nanocrystals are conducted in this thesis.We studied the crystallization of PbS QDs and Na₂SrSi₂O₆ nanocrystals and SrSiO₃ nanocrystals and the formation of core/shell nanocrystals in the glass,researched the optical properties and investigated the passivation of oxide nanocrystals on PbS QDs.Through melt-quenching method and heat-treatment method,we precipitated the PbS QDs doped glasses containing sodium strontium silicate?Na₂SrSi₂O₆?nanocrystals and strontium silicate?SrSiO₃?nanocrystals,and PbS/Na₂SrSi₂O₆ core/shell nanocrystals and PbS/SrSiO₃ core/shell nanocrystals were formed,and then we studied the effect of oxide nanocrystals on the optical properties of PbS QDs.The conclusions are as follows:?1?PbS QDs with average diameter of 5.7-11.4 nm,Na₂SrSi₂O₆ nanocrystals with average diameter of 30-50 nm and SrSiO₃ nanocrystals with average diameter of>100 nm were precipitated in the glasses through thermal treatment and glass compositions.?2?The growth behavior of PbS QDs in glasses with respect to compositions and heat-treatment temperatures and durations was monitored with absorption and photoluminescence spectra in the range of 1500 nm-2200 nm.?3?PbS QDs acted as nucleating agents for Na₂SrSi₂O₆ nanocrystals and SrSiO₃nanocrystals and promote their formation in glasses.?4?High resolution transmission electron microscopy analysis evidenced that PbS/Na₂SrSi₂O₆ core/shell nanocrystals and PbS/SrSiO₃ core/shell nanocrystals were formed in the glass.?5?In the glass without Pb,the S hinder the crystallization of Na₂SrSi₂O₆nanocrystals.In the glass with Pb and S,the increasing content of S or Pb can promote the crystallization of Na₂SrSi₂O₆ nanocrystals and SrSiO₃ nanocrystals.