Nobel Prize in Chemistry 2023: what’s in it for industry?

The 2023 Nobel Prize in Chem­istry was awar­ded for the dis­cov­ery and syn­thes­is of col­loid­al quantum dots. Three sci­ent­ists were awar­ded the prize: Aleksey Yekimov, Louis Brus and Moungi Bawendi.

These are nan­o­particles (particles of the order of 10^-9 metres in size, or one mil­lionth of a mil­li­metre) of semi­con­duct­or mater­i­al. What makes them spe­cial? Their prop­er­ties are determ­ined by their size. This is highly unusu­al: the prop­er­ties of mater­i­als are typ­ic­ally inde­pend­ent of their size. But it turns out that when the size is reduced to the nano­metre scale, it is pos­sible to obtain sig­ni­fic­ant vari­ations in elec­tron­ic prop­er­ties. This is called the phe­nomen­on of quantum con­fine­ment. It’s import­ant to under­stand that this prop­erty is truly incred­ible. Before their dis­cov­ery, the only way to vary the prop­er­ties of a mater­i­al was to change its composition.

Essen­tially, they are used as light sources. Quantum dots are excited when exposed to light. They then return to their fun­da­ment­al state by emit­ting a photon, an ele­ment­ary particle of light. The col­our of this photon depends very much on the size of the quantum dot. A pro­cess developed by Phil­ippe Guyot-Sion­nest, a former poly­tech­ni­cian, makes this pho­to­lu­min­es­cence pro­cess extremely effi­cient, with a yield close to 100%.

Yes, they can be found in QLED tele­vi­sions. Blue diodes excite the screen’s quantum dots to gen­er­ate the TV’s dis­play. Com­pared with con­ven­tion­al tech­no­lo­gies, col­our pur­ity is sig­ni­fic­antly improved. This is the main indus­tri­al applic­a­tion for quantum dots.

Oth­er pro­jects involve anti-coun­ter­feit­ing devices. By integ­rat­ing a mark using a quantum dot on the object to be cer­ti­fied, it is then pos­sible to eas­ily veri­fy its pres­ence using a light source. The advant­age: this device is dif­fi­cult to man­u­fac­ture and easy to handle. Finally, new applic­a­tions are emer­ging in the field of infrared detec­tion. By depos­it­ing quantum dots (which absorb infrared light) on a con­ven­tion­al cam­era read­ing cir­cuit, we can cre­ate an infrared cam­era. This tech­no­logy con­sid­er­ably increases sens­it­iv­ity. This applic­a­tion is still at the research stage, and sev­er­al man­u­fac­tur­ers, includ­ing the French com­pany ST Micro­elec­tron­ics, are devel­op­ing this type of camera.

Bio­lo­gists were quick to embrace the sub­ject. Quantum dots are used to study bio­lo­gic­al phe­nom­ena. How do they work? A bio­lo­gic­al spe­cies (such as a tox­in) is attached to a quantum dot. The quantum dot is then placed in a growth medi­um con­tain­ing cells. By illu­min­at­ing the sample, it is pos­sible to fol­low the tra­ject­ory of the tox­in thanks to the lumin­es­cence of the quantum dot. The obser­va­tion can be car­ried out over a long peri­od, unlike the obser­va­tion sys­tems pre­vi­ously used. Maxime Dahan, a French bio­phys­i­cist, has thus observed in vitro the phe­nomen­on of inform­a­tion trans­mis­sion at the syn­aptic level.

Quantum dots stand out from oth­er mater­i­als in two respects. Firstly, it is pos­sible to mod­u­late their absorp­tion and emis­sion prop­er­ties very pre­cisely by modi­fy­ing their size and chem­ic­al com­pos­i­tion. This is a very inter­est­ing prop­erty for lumin­es­cence applic­a­tions such as tele­vi­sions: all you have to do is change the size of the quantum dots to con­trol their emis­sion col­our. They can cov­er a very wide range of wavelengths, from 400 nano­metres to a few microns (vis­ible and infrared light).

In addi­tion, these are inor­gan­ic mater­i­als, which gives the sig­nal sta­bil­ity. The only short­com­ing is the blink­ing effect of the quantum dots. But it is now pos­sible to over­come this by using more com­plex syn­thes­is techniques.

The launch of QLED TV sets is proof that it is pos­sible to man­u­fac­ture them on an indus­tri­al scale. Their syn­thes­is is not a simple mat­ter. The dif­fi­culty lies in con­trolling the size of the particles. Their size – on a nano­met­ric scale – is mainly con­trolled by the tem­per­at­ure at which they are formed. On an indus­tri­al scale, it is there­fore neces­sary to main­tain a per­fectly homo­gen­ous tem­per­at­ure in large-scale reactors.

Thanks to the work of Aleksey Yekimov and Moungi Bawendi, two of the three Nobel Prize win­ners, we are now at the stage of indus­tri­al pro­duc­tion. The meth­od they developed revolu­tion­ised the chem­istry of nano­crys­tals and is now used to syn­thes­ise many oth­er mater­i­als such as iron oxide, tung­sten and titanium.

This research began in the early 1980s with the first exper­i­ment­al obser­va­tions. Aleksey Yekimov observed the vari­ation in the spec­tro­met­ric prop­er­ties of col­oured glass as a func­tion of the heat treat­ment of the mater­i­al. He was the first to make the con­nec­tion between the size of the small semi­con­duct­or pre­cip­it­ates he observed in glass and its prop­er­ties. This is a marked phe­nomen­on in glass, as it is vis­ible to the naked eye: when heat annealed at between 250°C and 400°C, a col­our gradi­ent is observed, from yel­low (small semi­con­duct­or crys­tals in the glass mat­rix) to red (large semi­con­duct­or crys­tals). Louis Brus was the first to explain the phys­ics behind the observed phe­nomen­on known as quantum con­fine­ment, by Aleksey Yekimov.

Moungi Bawendi, a stu­dent of Louis Brus, developed an advanced syn­thes­is meth­od. It was prov­ing dif­fi­cult to pre­cisely con­trol the size dis­tri­bu­tion of glass particles, and there­fore the prop­er­ties of the mater­i­al. Moungi Bawendi came up with the idea of man­u­fac­tur­ing crys­tals in col­loid­al sus­pen­sion, i.e. in a solvent. He mixes pre­curs­ors (cad­mi­um and sel­en­i­um) in a solvent, lead­ing to the form­a­tion of cad­mi­um sel­en­ide crys­tals. By car­ry­ing out this syn­thes­is at high tem­per­at­ure (250–300°C), the nuc­le­ation and growth of the crys­tals are very well con­trolled. This is the key to con­trolling the size and dis­tri­bu­tion of particles, and there­fore their prop­er­ties. His work has revolu­tion­ised the field of crys­tal pro­duc­tion using col­loid chemistry.

This remains a par­tic­u­larly act­ive field. Chem­ists are con­tinu­ing to improve mater­i­als and to pro­pose new strategies for the emer­gence of inter­est­ing prop­er­ties: applic­a­tions in cata­lys­is, in pho­tocata­lys­is for arti­fi­cial pho­to­syn­thes­is, the assembly of nano­crys­tals to form supra­c­rys­tals with new col­lect­ive prop­er­ties, etc. Research teams are also work­ing on the shape of quantum dots, mak­ing rods rather than spheres. This could pave the way for new applic­a­tions in bio­logy to bet­ter char­ac­ter­ise the flow of flu­ids such as blood. Phys­i­cists, for their part, are adopt­ing them because of their ultra-pure light-emit­ting prop­er­ties: research is look­ing into the use of quantum dots in quantum com­put­ing and quantum cryp­to­graphy. What’s more, thanks to their great flex­ib­il­ity and robust­ness, these quantum dots could become build­ing blocks for nanotechnology. 

Interview by Anaïs Marechal