FIELD

The present invention pertains to the field of nanocrystals with absorption properties in infrared range. In particular, the invention relates to mercury chalcogenide nanocrystals and a method to produce them from mercury thiolate compound.

BACKGROUND

Colloidal quantum dots (CQD) have striking properties in terms of light absorption and light emission properties. Control of size of these objects allows to design nanoparticles with varying bandgap energies, thus defining in which range of electromagnetic spectrum these nanoparticles will interact. Applications of such nanoparticles range from light emitters (LED, displays) to sensors and photoreceptors.

Two types of material have been considered for the design material interacting in infrared range of wavelength: lead (Pb) chalcogenides and mercury (Hg) chalcogenides. Lead chalcogenides (PbS, PbSe and PbTe) offer a limited spectral tunability due to their bulk band gap. Mercury chalcogenides are semimetal as bulk material and the energy of their infrared transition can potentially be reduced to zero. They consequently offer a much larger tunability and have raised much interest for infrared devices.

Chen et al. discloses HgTe quantum dots having a confinement energy less than 5000 cm−1and having a ratio of electron mobility and hole mobility greater than 1 (ACS Photonics, vol. 6, no. 9, p. 2358-2365). WO 2019/068814 discloses nanoparticles having a confinement energy greater than 5000 cm−1and does not disclose that these nanoparticles a ratio of electron mobility and hole mobility greater than 1.

However, current synthesis of mercury chalcogenide nanoparticles suffers from several drawbacks. Mercury precursors are usually based on HgII, which is highly toxic. In addition, it is difficult to obtain dispersions of mercury chalcogenide nanoparticles with high concentration. This is a major drawback in view of large-scale synthesis and access to cost effective products.

It is an object of the invention to provide with a method yielding concentrated dispersions of nanoparticles, optionally using mercury at oxidation state zero, i.e. less toxic than HgII.

Mercury telluride nanoparticles with improved properties have been also obtained.

SUMMARY

This invention thus relates to a method of preparation of mercury chalcogenide nanoparticles HgX comprising the steps of providing a precursor of Hg and mixing said precursor of Hg with a precursor of X, wherein precursor of Hg is a Hg thiolate and X is a chalcogenide.

In an embodiment, mixing is done in a coordinating solvent, preferably an amine, more preferably oleylamine.

In an embodiment, X is a chalcogenide selected from Tellurium (Te), Selenium (Se) and Sulphur (S), preferably X is Te.

In an embodiment, precursor of X is selected from trioctylphosphine telluride (TOPTe); ammonium sulfide (NH4)2S and elemental Se.

In an embodiment, Hg thiolate is a salt of Hg at oxidation state +II.

In an embodiment, Hg thiolate is prepared by reaction of liquid Hg with thiol, preferably under sonication conditions.

In an embodiment, an oxidizing agent is added during reaction of liquid Hg with thiol, preferably oxidizing agent is iodine I2.

The invention also relates to HgTe nanoparticles having a confinement energy greater than 5000 cm−1and having a ratio of electron mobility and hole mobility greater than 1, preferably greater than 5. Preferably, these HgTe nanoparticles are capped with thiols.

The invention also relates to HgTe nanoparticles having a confinement energy less than 4000 cm−1and having a ratio of electron mobility and hole mobility less than 1, preferably less than 0.1. Preferably, these HgTe nanoparticles are capped with thiols.

The invention also relates to the use of said HgTe nanoparticles in an IR photodetector, an IR photoconversion device, an IR filter or an IR photodiode.

The invention finally relates to an optoelectronic device comprising said HgTe nanoparticles, preferably optoelectronic device is selected from an IR photodetector, an IR photoconversion device, an IR filter or an IR photodiode.

