Craig Bullen

Synthesis of Tunable, Highly Luminescent QD‐Glasses Through Sol‐Gel Processing

Photostable quantum dot (QD)-glasses for use in optical devices can be prepared by solution-phase synthesis of the luminescent material followed by sol-gel processing, to embed the semiconductor particles in silica. Prevention of surface reactions that slowly quench the luminescence and degrade the QD is a key problem of their production. A solution to this was found in octylamine, which, when added during the sol-gel processing, not only passivates the surface of the QD but also accelerates the gelation process. CdSe QDs capped with ZnS thus treated remain luminescent over several months.

Three-photon excited band edge and trap emission of CdS semiconductor nanocrystals

We report on three-photon excited band edge and trap emission of CdS semiconductor nanocrystals. While the band edge emission intensity clearly shows a cubic dependence on excitation intensity, demonstrating three-photon absorption process, the trap emission does not exhibit such a cubic dependence. A simple theoretical model based on the assumption that there exist a limited number of trap states in nanocrystals shows good agreement with the experiment, suggesting that the number of trap states play an important role in their emission intensity dependence of multiphoton excitation. The three-photon absorption cross section of CdS nanocrystals is measured to be ∼10−79 cm6 s2 photon−2, which is three to four orders of magnitude higher than those of the previously reported common UV fluorescent dyes.

Incorporation of a highly luminescent semiconductor quantum dot in ZrO2–SiO2 hybrid sol–gel glass film

In this paper we describe a method for transferring semiconductor quantum dots, produced in non-polar solvents by an organometallic approach, into sol–gel matrices. ZrO2–SiO2 hybrid sol–gel glass films have been homogeneously doped with different semiconductor quantum dots (CdSe, CdSe@CdS and CdSe@ZnS). Both the absorption and the emission properties of the semiconductor nanocrystals are only slightly affected by the incorporation into the sol–gel matrix. The doped films showed sufficiently high refractive index for the realization of planar waveguides.

Two-photon-induced three-dimensional optical data storage in CdS quantum-dot doped photopolymer

The authors demonstrate three-dimensional erasable bit optical data storage in a quantum-dot doped photopolymer under two-photon excitation by a near-infrared femtosecond pulsed laser beam. It is shown that the photorefractive polymer consisting of poly(vinyl carbazole), ethyl carbazole, 4-(diethylaminobenzylidene)-malononitrile, and CdS quantum dots exhibits the changes not only in refractive index but also in fluorescence. Such a photosensitivity provides a multimode readout mechanism. In particular, the use of S rich surface quantum dots not only allows the two-photon-induced bit optical data storage with greater contrast but also expands the margin between permanent and erasable recording thresholds.

Two-photon fluorescence scanning near-field microscopy based on a focused evanescent field under total internal reflection

We present two-photon fluorescence near-field microscopy based on an evanescent field focus produced by a ring beam under total internal reflection. The evanescent field produced by this method is focused by a high-numerical-aperture objective, producing a tightly confined volume that can effectively induce two-photon excitation. The imaging system is characterized by the two-photon-excited images of the nanocrystals, which show that the focused evanescent field is split into two lobes because of the enhancement of the longitudinal polarization component at the focus. This feature is confirmed by the theoretical prediction. Unlike other two-photon near-field probes, this method does not have the heating effect and requires no control mechanism of the distance between a sample and the probe.

A seedless approach to continuous flow synthesis of gold nanorods

A direct seedless method for the continuous synthesis of gold nanorods has been developed using a sequential rotating tube-narrow channel processing microfluidic configuration, with the stock feed solutions (HAuCl(4)/CTAB/acetylacetone and AgNO(3)/CTAB/carbonate buffer) being stable for weeks.

Metallic nanorods doped optical recording media: The use of nanorods as nano-heat sensitizers

In this study, we demonstrate the gold nanorods can be successfully incorporated into common optical recording media such as phthalo-cyanine, azo-dye, and phase change media, and operate as a nano-heat sensitizers. Since the recording mechanism for optical recording media is optothermal energy conversion, high absorption cross section of gold nanorods tuned at recording laser wavelengths is shown to be extremely useful in nano-heat generation, which facilitate the efficient recording on those media.

Incorporation of Quantum Dots into 3D Photonic Crystals for Emission Control

This article demonstrates infiltration and doping as two efficient and flexible methods for incorporation of PbSe quantum dots (QDs) into three-dimensional (3D) photonic crystals. QDs induced photonic band gap shift was observed by the infiltration method. By employing the two-photon polymerisation technique, 3D photonic crystals were fabricated with QDs doped resin. Investigation will be focused on radiation dynamics and emission control of QDs in 3D photonic crystals

Functionalisation of gold nanorods and its application to optical data storage

In this report we show the application of silica coated gold nanorods to optical data storage. We show controlled growth of a thick silica shell onto gold nanorods. The coated nanorods are transferred into a PVA matrix and data patterns are recorded. A silica layer on the nanorods dissipates the heat and the matrix does not melt, allowing reliable data storage.

Two-photon induced optical recording in quantumdot-based photorefractive materials

In this paper we report on two-photon-excited bit by bit data storage within a photorefractive polymer composed of 53.9 weight percents of PVK (poly(N-vinylecarbazole)), 30wt% of DMNPAA (2,5-dimethyl-4-(p-nitrophenylazo)anisole), 16wt% of ECZ (N-ethylcarbazole) and 0.1 wt% of CdS quantum dots as a sensitizer. Multi-layer data sets with a layer spacing 20 mu are recorded using a pulsed ultrashort laser at a wavelength of 780 nm