Acid-free sol-gel fabrication of glass thin films embedded with II-VI colloidal quantum dots

Hemang Jani,Lingze Duan

doi:10.1117/1.jnp.9.093072

Abstract

II-VI colloidal quantum dots (QDs) are ideal for optical sensors thanks to their high fluorescent brightness and good size uniformity. However, embedding colloidal QDs into a glass matrix with the standard sol-gel process leads to the QDs being damaged by the acid catalyst. Here, we report an acid-free sol-gel technique, which proves to be both simple and effective in fabricating silica glass thin films embedded with commercial II-VI colloidal QDs. Octadecylamine ligands are used as a bifunctional aid to not only stabilize the QDs in solution, but also assist the formation of the SiO2 gel. We demonstrate that high-quality QD-embedded glass thin films can be developed with this technique, and our fluorescent tests indicate that, except for a small blueshift in the emission spectrum, the QDs are very well preserved through the sol-gel process. This method offers a fast and low-cost path towards thin-film QD sensors with good mechanical and thermal stabilities, which are desirable for applications involving highly focused laser beams, such as ultrafast nanophotonics.

Highlights

One particular aspect that draws our research interest is the possibility of using quantum dots (QDs) as solid-state quasi-two-level systems, whose interaction with femtosecond optical pulses can potentially lead to some interesting phenomena, such as carrierenvelop phase (CEP) sensitive population inversion.[3,4]
We report a systematic study of sol-gel fabrication of QD-embedded glass thin films, focusing primarily on using commercial cadmium selenide (CdSe) QDs
Our study shows that the standard procedure of making sol-gel glass, which involves the use of acid catalysts such as hydrochloric acid (HCl) or CH3COOH or HNO3

Summary

Introduction

Semiconductor quantum dots (QDs) offer many unique optical properties owing to their strong spatial confinement of the charge carriers.[1,2] One particular aspect that draws our research interest is the possibility of using QDs as solid-state quasi-two-level systems, whose interaction with femtosecond optical pulses can potentially lead to some interesting phenomena, such as carrierenvelop phase (CEP) sensitive population inversion.[3,4] The unique features of CEP post several challenges to the QD-sensor development. Good size uniformity is needed for the QDs to limit inhomogeneous line broadening, and the active layer must be both thermally and mechanically stable under a tightly focused laser beam. All of these requirements can be met by using chemically synthesized II-VI colloidal QDs embedded in a transparent buffer material (matrix), such as SiO2 (glass) or TiO2, and coating the QD/matrix complex on a substrate.[5,6] The sol-gel method is an effective technique to develop such QD thinfilm sensors.[7,8,9]. Given the excellent performance and wide availability of today’s commercial II-VI colloidal QDs, this technique potentially opens up a path towards simple, fast, and low-cost development of QD–glass complex systems

Sample Fabrication

Sample Characterization

Findings

Conclusion