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