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Enhancing Lasing Properties Of CdTe Quantum Disks

Suitable for use in lasers, a novel preparation method of cadmium telluride quantum disks can leads to more stable nanocrystals compared to conventional preparation methods. Tuning the shape of the disks can strongly improve conditions for lasing or single-photon emission
Researchers have used a novel synthesis method to produce hexagonal CdTe nanocrystals from disk-shaped Cu2Te nanocrystals.



Schematic showing disk-shaped hexagonal Cu2Te nanocrystals and subsequent cation exchange of Cu to Cd at high temperature (180 °C) resulting in highly fluorescent CdTe nanocrystals

The Cu2Te nanocrystals have a well-defined stoichiometric composition and tuneable diameter and thickness. The resultantCdTe has less than 1 mol % of residual Cu remaining in the lattice.

The synthesis preserves the overall disk shape, but is accompanied by a substantial reconstruction of the anion sublattice. This results in a reorientation of the c-axis from the surface normal in Cu2Te into the disk plane in CdTe nanodisks.



TEM micrographs showing Cu2Te (left) and CdTe (right)

The scientists from the Istituto Italiano di Tecnologia, Genova and IMEM-CNR, Parma in Italy, used the FLS920 photoluminescence spectrometer made by Edinburgh Instruments to measure the photoluminescence (PL) spectral properties, quantum efficiencies and lifetimes of the CdTe disks.

Fluorescent nanocrystals are currently being applied in lasers or displays, and offer exciting prospects for future photonics such as quantum emitters. The nanocrystal shape plays an important role in these applications. The flat CdTe quantum disks with high fluorescence efficiency therefore provide an interesting possibility to explore the shape- and crystal structure-dependent fluorescence properties of semiconductor nanocrystals.

The measurements conditions could be carefully controlled using the FLS920: the PL quantum efficiency of the CdTe quantum disks was measured with an integrating sphere, by exciting the samples at 500 nm.

Band-edge PL lifetime measurements were made with the FLS920 using time-correlated single-photon counting, exciting the samples at 400 nm with a 50 ps laser diode. The repetition rate of the diode was adjusted to 1 MHz to ensure complete decay of the emission between subsequent excitation pulses.

The disks show a PL peak that can be tuned continuously from 600 to 640 nm according to their thickness. The researchers also reached a faster PL decay time compared to spherical CdTe quantum dots, which confirms that simply tuning the shape can strongly improve conditions for lasing or single-photon emission. What's more, the current synthesis also leads to more stable nanocrystals compared to conventional preparation methods, opening up the way for practical application of the quantum dots.



The CdTe nanodisks show a continuously tuneable PL peak position, scaling with the thickness of the disks

The results were recently published in the paper, "Synthesis of Uniform Disk-Shaped Copper Telluride Nanocrystals and Cation Exchange to Cadmium Telluride Quantum Disks with Stable Red Emission," by Hongbo Li et al in Journal of the American Chemical Society . http://dx.doi.org/10.1021/ja404694k

 



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