In this work, we study the size-dependent properties of Photoluminescence (PL) emissions of PbSe Nanocrystals (NCs) grown by Chemical Bath Deposition (CBD) method. In previous studies, PL emissions have been tuned by CBD-grown PbSe, and the growth mechanism was dependent on crystalized substrates such as GaAs. In this research, however, PL emissions are controlled over the midinfrared (MIR) range, through PbSe NCs, which are deposited on glass as an amorphous material. This study proposes an alternative approach to control PL emissions, which provides us with more freedom to fabricate low-cost MIR light sources as crucial components in remote sensing and gas analysis. Moreover, in this study, the advantage of the post-thermal method to control the NCs size, compared to the growth temperature, is shown.
Mid-infrared spectrum is known as the "molecular fingerprint" region, where most of the trace gases have their identical absorption patterns. Photonic crystals allow the control of light-matter interactions within micro/nanoscales, offering unique advantages for gas analyzing applications. Therefore, investigating mid-infrared photonic crystal based gas sensing methods is of significant importance for the gas sensing systems with high sensitivity and portable footprint features. In recent various photonic crystal gas sensing techniques have been developing rapidly in the mid-infrared region. They operate either by detecting the optical spectrum behavior or by measuring the material properties, such as the gas absorption patterns, the refractive index, as well as the electrical conductivities. Here, we will brief the progress, and review the above-listed photonic crystal approaches in the mid-infrared range. Their uniqueness and weakness will both be presented. Although the technical level for them has not been ready for commercialization yet, their small size, weight, power consumption and cost (SWaP-C) features offer great values and indicate their enormous application potentials in future, especially under the stimulation of the newly emerging technology "Internet of Things" which heavily relies on modern SWaP-C sensor devices.
In this work, we present a theoretical study on using high contrast grating (HCG) designs to enhance light–gas interaction in the mid-infrared range. The optical behavior of a single layer HCG was studied under the presence of CO2 gas. Through optimizing the structure parameters, we could confine an intense electric field over the grating layer. Consequently, about 200 times of light-absorption enhancement was observed. To further improve the performance, a coupled HCG (CHCG) was proposed to introduce another vertical photonic confinement mechanism. We found that CHCG can restrict much intense light energy in the structure leading to over 600 times of light-absorption enhancement. However, it is noticed that a significant part of the concentrated electric field was still trapped in the high index areas, where the gas cannot interact. To address this issue, a modified CHCG with a thin substrate thickness was proposed. Through the optimization (T=1.149μm), we were able to redistribute most of the light energy into the void space of the CHCG layer which resulted in close to 1400 times of improvement. This work clearly demonstrates that using HCG for enhancing light–gas interaction is a promising approach to make on-chip gas sensing devices. Furthermore, it can also be integrated into other photonic components, e.g., fibers for advanced sensing system development.
A direct oriented-attachment (OA) growth of lead-chalcogenide nanocrystals (NCs) on amorphous substrates leads to the synthesis of (111) dominated PbSe NCs for the first time. These NCs uniformly assembled on glass slides forming mirror-like thin films of tunable quantum confining effect in the mid-infrared spectrum.
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