Photoluminescence of colloidal CdTe quantum disks evaluated

Livingston, Scotland--Researchers at the Istituto Italiano di Tecnologia, Genova and IMEM-CNR, Parma in Italy have used a photoluminescence spectrometer from Edinburgh Instruments (the FLS920) to measure the photoluminescence (PL) spectral properties, quantum efficiencies, and lifetimes of novel cadmium telluride (CdTe) semiconductor quantum disks synthesized from disk-shaped copper telluride (Cu₂Te) nanocrystals.

Fluorescent nanocrystals can be used in lasers or displays, and offer prospects for future photonic devices such as quantum emitters. The shape of the nanocrystal plays an important role in these applications. Flat CdTe quantum disks with high fluorescence efficiency therefore provide an interesting way to explore the shape- and crystal-structure-dependent fluorescence properties of semiconductor nanocrystals.

The measurement 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 disks had a shorter PL decay time than spherical CdTe quantum dots, which confirms that simply tuning the shape can strongly improve conditions for lasing or single-photon emission. In addition, the current synthesis leads to more stable nanocrystals compared to conventional preparation methods, opening the way for practical application of the quantum dots. The results were recently published in the Journal of the American Chemical Society (http://dx.doi.org/10.1021/ja404694k).