Temperature-Dependent Photoluminescence of CdS/ZnS Core/Shell Quantum Dots for Temperature Sensors

Abstract

Exploring the temperature-dependent photoluminescence (PL) properties of quantum dots (QDs) is not only important for understanding the carrier recombination processes in QD-based devices but also critical for expanding their special applications at different temperatures. However, there is still no clear understanding of the optical properties of CdS/ZnS core/shell QDs as a function of temperature. Herein, the temperature-dependent PL spectra of CdS/ZnS core/shell QDs were studied in the temperature range of 77–297 K. It was found that the band-edge emission (BEE) intensity decreases continuously with increasing temperature, while the surface-state emission (SSE) intensity first increases and then decreases. For BEE intensity, in the low temperature range, a small activation energy (29.5 meV) in the nonradiative recombination process led to the decrease of PL intensity of CdS/ZnS core/shell QDs; and at high temperature the PL intensity attenuation was caused by the thermal escape process. On the other hand, the temperature-dependent variation trend of the SSE intensity was determined by the competition of the trapping process of the surface trap states and the effect of thermally activated non-radiative defects. As the temperature increased, the PL spectra showed a certain degree of redshift in the peak energies of both band-edge and surface states and the PL spectrum full width at half-maximum (FWHM) increases, which was mainly due to the coupling of exciton and acoustic phonon. Furthermore, the CIE chromaticity coordinates turned from (0.190, 0.102) to (0.302, 0.194), which changed dramatically with temperature. The results indicated that the CdS/ZnS core/shell QDs are expected to be applied in temperature sensors.

Composition effects on exciton recombination dynamics of blue-emitting alloyed Cd1−xZnxS/ZnS quantum dots

“…The bandgap shrinks in semiconductor nanostructures are usually analogous to that of bulk semiconductor structures and ascribed to exciton phonon coupling and lattice deformation. 19 The temperature dependence of the bandgap in bulk polar semiconductors mainly takes place via Fro ¨hlich interaction and the strong electron (hole)-lattice interaction results from the polarization of the lattice, which is produced mainly by the longitudinal optical modes. 20 The deformation potentials are usually negative for II-VI semiconductors accounting for part of the bandgap shrinks with increasing temperature.…”

Shell thickness-induced thermal dependence: highly sensitive core–shell CdSe/ZnS/POSS-based temperature probes

“…[20][21][22] To overcome these drawbacks, further applications of quantum dots have been rendered feasible with the development of a series of sensors based on surface optimization and other fluorescence features (peak intensity ratio, peak wavelength, full width at half maximum, etc.) [23][24][25][26][27][28] Nevertheless, most of the previously reported studies have concentrated on the material selection and appropriate management of synthesis conditions, but relatively little investigation has been carried out into the variables affecting the temperature characteristics of quantum dots.…”

pH sensing, bioimaging, and fluorescence lifetime imaging microscopy using polyethyleneimine coated carbon dots and gold nanoparticles

“…Research into the environment, medicine, and biology increasingly depends on materials having multiresponsive optical characteristics (pH, temperature, and solvents, concentration). For instance, the great majority of biomolecules found inside cells are governed by temperature in terms of their dynamics and reactivity 6 . At the cellular level, pH is crucial for numerous cellular processes, including cell migration, ion transport, calcium control, proliferation, apoptosis, and response to therapy.…”