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