 to da je veliko pedagogisk vziv. V zelo se zelo zelo izvihne od vsoočenja. Tukaj je zelo s energijem, je to zelo, da je zelo, koncentrujno zeljene energij in 50 nr. v 1940. A bil ti ničt Trying that natural gas, petroleum, are going to be decreasing the consumption. There is decreasing the use of coal, and of course it is getting rITYce. But still for many years to go in decades we have to rely on fossil fuels. Which of course opens the big problem, because we know that these has a lot of consequence Tudi niče začali, da je tudi 50 rov in 50 do 2000 rov, da je vzvečnja vzvečne vzvečnja v CO2 in vzvečnja vzvečnja in tudi 100 ppm, ki je zelo jaz nekaj različ. Znamenimo, da dobro se vzvečnje vzvečnja vzvečnja vzvečnja, da znamenimo, da se vzvečnja vzvečnja vzvečnja vzvečnja vzvečnja. Tukaj ne lahko ne poživajo, ne lahko ne opravil, a tako da pridemo zelo zelo, če je to lepo, nekaj je zelo zelo obržen, nekaj nekaj nekaj kemika in nekaj nekaj nekaj spljenja. Tako je tukaj nekaj nekaj nekaj, da poživajem vsem. Ne꽤em, da se nekaj nekaj načo je izgleda, da je zelo prišel in je pošel in nekaj nekaj nekaj. Zato sem tukaj izgleda, da je to državno pravno stavlje. To je tega vsoša vsoša, da jsi ne zavljeliš diskussion o tem v nekaj nekaj nažal, ali na medija, da vse. Vse jih je da vse poštila, je tukaj razljavno izgleda, pa nisem si nekaj nekaj, da so nekaj pristim, da se ne poštila. Vesem, ta ideja in pravično, tudi ideja, že se vsoša je zelo zelo pošte, ker v prinesiplji lahko se početite CO2 in se reakvite s 3 molj, 1 molj CO2 in 3 molj z hidrogen in se predajte metanol in vod. Metanol je vsefjuel, je vsefjuel, je bilo konverter, ali je zelo vsefjuel vsefjuel. Vse proces je zelo vsefjuel. Vsefjuel je zelo vsefjuel vsefjuel. in rejuvala. Narednjih, da se počutimo, hidrogen je produsil industrijno v veliki mene, ali je produsil v poslutnih vsev. V procesu, kaj je izgleda stejne reformenje. In vse proces je nekaj zelo zelo, tudi nekaj plant v vsev, kaj je produsil metanol, izgleda z CO2. To je v 2014. To je basa na katalistu, kaper on zinkokaj, in je zelo na geotermalj energiji. To je zelo v Izlanu, ker je nekaj energij, in da je taj reakcij vzelo. To je tudi tudi termal katalizist. Zato vse je zelo energij, kaj je zelo na konverciju vzelo na eksternosti energij. Zato, kaj je zelo vzelo, ne binjo se načo zelo nekaj zelo ga kaj je zelo let v soli. Ciske, to je in zelo bila vzelo, ker CO2 je počkega instavna formda kareljina, kako njiha s počkom oxidico, je vkaj najboljših energijskih stajnih, zato termodinamik kljenjo. In zato s enami s hodim vzelo, da se vzelo, da igram vzelo zbredne in zelo, hrvom način nošu z vse boj gržovac, ki se prejdi in je zloženje doprav, zašeljaju nekaj ili neko v podstav inverteri. Vse je neko na konferenciji, ki mali da nekaj prejdi tising, večno neč nekaj reagirujemo vsakrana termodinamika, nekaj k seinem da neč nekaj prejdi מי filloves. Nisem s edmirationem, Vzdaj, kaj je bi bilo napotno, da sem bilo upril termodynamics. Tako je ni veliko, ni veliko dobro. Tukaj je svojezdi, ko je svojezdi s CO2 in fuel-ovnimi energijami. Vseš da se razstavila, da je bilo oto, da se to vzajča v prišločenu. Svojezdi, da imaš karboni, dioksaj, voda in vzajščenu vzajščenu. Vzajščenu vzajščenu, kaj bi začel se obrada vzajščenu, prej cannot convert this in glucose and oxygen. And since somebody has, I am sure he was going to talk about nature of photosynthesis, I will not address the complexity of this process, which are weather accustomed in nature and this is the result of a million years of evolution. Now, of course people are trying to design what is called the artificial photosynthesis. je to včešnja najbolj, da se je zelo naši dobroči, naši je nekaj, ki se je zelo v rojče, v ko je naši dobroči CO2, in kako je hodnjela, zelo naši dobroči. Včetno. Zelo našem pravda, da ima nekaj izgleden. Včetno, da, ki se zelo naši dobroči in nekaj, svarz izgleda energija za in izgleda tudi in zelo jaziljamo ljub. Vsih tudi je to tukaj o potopi katalizacij. Zelo ideje, ki me izgleda tako poni del, je vse občasno, lahko jaziljamo ljub in tudi stažimo elektron in vzelo. Tudi, kaj jaziljamo atom, jaziljamo elektron in jaziljamo zelo pozitiv. In tudi bolje bolje bolje, ki je separati v elektronici, to če in elektronici, moj držaj se nalivati na vsek. in reacijo s kamikvom vsek. Ko ni teči, naredite nekaj kamikv. To je ideja, ki je odlično. Foto katalizit se poživajo na 2 vrste. Because you can use these ideas of capturing light and generating electrons and holes on one side to produce what is called environmental catalysis. What is this? Well, you generate these electrons and holes, you have species which are pollutants which are in the air or in water, and you use these electrons and holes to transfer them to these molecules and induce chemical reactions and remove the pollutants. This is relatively easy because you want to go in the direction that thermodynamic suggests. So you want to reconvert molecules which are, for instance, toxic into CO2. In this case you want to produce CO2 because this CO2 molecule is not, is harmful for us. So we can use this to eliminate pollutants and it's relatively simple because it occurs with a single chart transfer. You can transfer one electron or you can transfer a hole and you start and you produce radical species and these radical species further react. Much more complicated is to basically use the same principle, generate electrons and holes to produce fuels, hydrogen or methanol or methane from CO2 and water. Because you need multiple chart transfers and you need to go against thermodynamics. So there are two fields which are both based on photoactive materials. One is environmental photocatalysis and one is production of fuels from solar energy. Now everybody is familiar, many people are familiar with this diagram but still I have to basically illustrate it because it is the basic of everything. So again, what happens when you have a nanoparticle, this can be an oxide, nanoparticle can be one of the most popular oxides, I will talk about this TIO2, but is in water, you have light, visible light or solar light, you generate electrons and holes. Are you generating electrons and holes? Because the material has some occupied states, the valence band and you excite an electron into the empty states, the conduction band. So the first requirement is that this jump, this transition has to occur in the visible range of light. First requirement, is that sufficient to make useful things? No, because then you need that the electron has to be transferred to the proton in water and the proton is reduced to hydrogen. And so you can induce the reduction of hydrogen or protons to hydrogen only if this electron is above the redox potential of water. And this is the second requirement. So the position of the conduction band has to be above this light. Then you have the holes. What can you do with the holes? In water, oxygen is in reduced state, is formally O2 minus. You generate an hole in the valence band because you have excited an electron. One electron is transferred back to the valence band or if you want, the hole migrates to the oxygen. And you form all minus pieces and then all pieces and from all pieces you form O2, you oxidize water. But this can only occur if the valence band of the semiconductor is below this threshold. And this is the third requirement. And you see, you need something which already has three requirements. And then if you generate this electron and the hole, they have to migrate to the surface of the nanoparticle. And in the process of migrating these electrons and holes, they can recombine, they can come together and basically fill the hole, the electron fills the hole and the process is stopped. And this is the fourth requirement. You need a low recombination rate. Otherwise you lose most of your electron hole pairs. So this is the basic. And how can we follow this process? Well, I'm not going to talk much about this particular technique which is called electromagnetic resonance or electron spin resonance. But you can follow the spin of electrons with this technique. And if you take, for instance, a TiO2 semiconductor and you take the spectrum in dark, there is no signal, then you irradiate your sample and you see there is a new signal, this signal which indicates the formation of O minus. O minus is radical. It has an unpaired electron. Or you excite electron into the conduction band and you form a titanium 3 plus ion. Again you have one unpaired electron titanium and you have another signal. So with this spectroscopy you can clearly see the generation of electrons and holes during your excitation process. OK, now, so if we have the right semiconductor we can start thinking of producing solar fuels. Hydrogen is the first of solar fuels. Of course many years ago, 20 years ago there was a lot if you go back in the newspapers. You will find that everybody was expecting the hydrogen car. In Milanova we wanted to build a gas station for hydrogen station. We still have the area. And everybody was convinced that hydrogen would have been the future. Actually that was not the case. Hydrogen economy would be fantastic because of course we could produce hydrogen from water and then use it in storage and use it for transportation and then using combustion and we regenerate water. So it's a very clean process. Today all the hydrogen which is produced doesn't come from splitting of water. It comes from steam reforming. So huge amounts of oil or natural gas are converted at very high temperature. For instance, methane plus water you form CO plus hydrogen. CO farther reacts with water and you form CO2 plus hydrogen. So when we produce hydrogen today we produce CO2 in the same way and we consume fossil fuels. And I visit one of these plants for instance in Ludvigshaven where Bayer has this huge chemical plant 7 kilometers wide, 2 kilometers large so in immense. And the first step they do is steam reforming. They produce a huge amount of hydrogen because hydrogen is needed for instance to produce ammonia which is another very important chemical reaction to produce fertilizers. So this is a problem. Today all the hydrogen is produced in this way. Of course you can produce this also biologically but the efficiency is low or in here we come to the topic photochemically and photo generation so you can use for instance in a semiconductor, TiO2 and you have light coming in and you generate these electrons and holes and you can produce oxygen on one side and hydrogen on the other side. And you can go to a web you can find many nice movies that show very clearly you just need this catalyst and you put it in water and you see the bubbles of hydrogen and oxygen coming out. The problem is that the efficiency is very low. Now this brings to the first problem which are the catalysts that we can use for this process, which are the materials. Now the first observations and a lot of literature is about titanium dioxide, TiO2. Well if you go again to the history you will find out that TiO2 is used since a century because it was used as an additive to paints already 1920. And already 1920 people realized that because it imposes optical properties of the paint so here there is a lot of TiO2 in this paint. But what also was recognized at that time that exactly because TiO2 is photoactive after sometimes it was inducing what is called chalking. In some light it can deteriorate the paint because in the paint you have also some organic component. And in 1921 there was a first report that TiO2 can interact with light and can induce in this particular case a reduction of TiO2. And you can find very accurate studies about the photoactivity of titanium dioxide in 1930s and 40s. So it's nothing new, let's say. It's quite well known. And the first report of the possible production of hydrogen from water electrolysis is from 1972 and coming back to the talk I gave yesterday is an interesting paper to read because it was less than two pages long. Five references. It is now highly cited. I think such a paper today will not go through the pre-review process because almost nothing is written in this paper. They simply said we suggested what can be decomposed by visible light into oxygen and hydrogen without application of any external voltage. So it was very interesting paper but it's very simple. But this is the idea. So the idea is not new. And after 50 years we are still debating what can be done and why it is not so efficiently done. Well, I was telling you the four requirements. And this is TiO2, TiO2 has two structures who tied or annotate. In both the band gaps, so the excitation, is between 3 and 3.2 electron volts. And if you look at the solar spectrum you realize that the number of visible light photons in the coming from the sun is just a very small fraction. So with this material we can only use this very little amount of photons which are able to excite electrons from the valence band to the conduction band. This is the first drawback. It is the first problem. Of course you can say, well, let's move out from TiO2. Let's take another semiconductor. And of course there are tables and theoreticians have done a lot of work in this field. You can compute or can you measure the properties of the various semiconductors in one of the second requirements. TiO2 is a good band gap which is a bit too large. It has a good position of the conduction band which is above the water reduction potential or of the valence band which is below the oxygen, oxidation potential. But of course there are other semiconductors with smaller band gaps so they absorb more visible light. But for instance the position of the conduction band is too low and the water condition of the valence band is too high. And you can also have materials which on paper are perfect. They have the right band gap and the right position of the valence band and conduction band. So why they are not using that? Well, first of all, you have to measure the real photoefficiency. And if you measure the real photoefficiency which means how many molecules of hydrogen we are producing per photon and how much photocurrent we are generating with irradiation. Well, for instance, you see TiO2 is here very low efficiency for the reasons that I mentioned to you. You may have better materials but you have, it's not enough to have the right position of the conduction band and valence band and band gap, you have very combination and the recombination reduces severely the efficiency and recombination, as I told you, there was a very beautiful lecture yesterday by Giulio Czerullo, so essentially it occurs in two ways. You can either recombine electrons and also generate photons as a mission of photons or you just have non-radiative recombination and you just increase the vibration and moles of your lattice. But even if you have the right material with the right band gap and the low recombination, is that solved the problem? There are also materials which are stable in working conditions which means liquids at various pH. So you need a material which does not dissolve when the pH becomes too acid or too basic. So this is the stability of the semiconductor is a very important issue. And that's why TiO2 is so much used because it's stable, it's non-toxic, it's basically it has a number of properties. And so people started to say, okay, let's follow another way. Let's take materials which are, I mean, not ideal but a good starting point and modify them, for instance, by doping. So let's see what can you do with doping. So the idea of doping, doping means when you have a material and you add a natural atom, whatever, it can be a metal, it can be a non-metal and this atom can enter either in the lattice replacing one of the existing atoms or can go in interstitial positions that depends very much on the synthesis and it's not the same, but of course this is just one possible thing. And what happens when you dope your material? Okay, here is a very important conceptual illustration. This is the starting material. You have a valence band, you have a conduction band and you have a given absorption of light, if you are below the threshold and then you have a suction. Now you introduce a dopant. The dopant can introduce a level in the band gap and then you can excite from this state to the conduction band and this can be done in visible light, much more efficient or you can introduce an empty level in the band gap and you can excite from here to here. So these are all phenomena which are absent in the pristine material and if you have this kind of situation you start to see that the absorption occurs at lower energy so you start to have to capture photons of visible light. There is another possibility where by doping the material and changing the electronic structure you just shift, you notice that this band is shift to higher energy so you move the entire band and you reduce the band gap and you have simply a shift of the entire absorption. Let me anticipate that this is really what we would like to have to modify the valence band and move the entire band. Unfortunately, this is what happens in most cases and I will be more specific about that. So there is another problem and this is a typical if you want a problem but I think it also has a lot of consequences which has to do with the localization, we generate an electron and a hole. Now, this is a picture which shows there is an electron in the conduction band so you have excited your electron the electron can be delocalized what does it mean, it belongs to the entire lattice it is these yellow signs which are basically spread over all atoms or it can be localized what does it mean it is sitting on a single ion and you see that there is a distortion of a lattice around it well when you have this localization you gain energy we gain energy and this is called a polaron it is a polaronic state the lattice distorts in order to trap the electron and localize it well, you realize that two situations are quite different here is an electron in a specific site here is an electron which is spread over the entire material and in terms of conductivity this is really quite a lot of consequences the same occurs for the hole you can generate a hole so you can form a single hole and you see this is the typical shape of a p orbital of an oxygen atom in the valence band which can be localized or can be delocalized but again the localization of a system and to the formation of a polaron now the nature the localized or delocalized nature of electrons is crucial in this kind of processes and this brings me to the topic of theory I will not speak of theory of these systems just a few general very general concepts of course nowadays most of electronic structure calculations are based on what is called density functional theory but the only message I want to give to an audience which I guess probably is mostly of experimentalist is that there are many variants of density functional theory they are not all the same and there is a hierarchy of accuracy in the methods that you are using and this problem of localization of delocalization critically depends on the level of theory that you are using to describe your material general most classical approaches are the so-called LDA or GGA functionals but if you really want to describe properly this phenomena and the localization of electrons and holes you have to go to higher levels in particular to what are called the hybrid functionals which are more or less at this level in this ladder now let me give you an example of what I am trying to describe this is again a case of TiU2 this is absorption band of TiU2 which as we have seen start to absorb above 3V if you dope with metal with transition metal iron tungsten chromium or vanadium you have to start to absorb higher wavelength which means lower energy photons now why is that if you do a calculation with an LDA or GGA functionals so you take for instance chromium doped TiU2 which means you put a chromium instead of a titanium in the lattice what happens? you have a valence band you have a conduction band and you have a new state which are due to this chromium doped if you look at this picture it looks like you have a small band which would be good actually which is crossed by the Fermi level but this picture is incorrect and this would lead to a delocalize nature of electrons why in reality the electrons are strongly localized and we have strong localization these levels have different positions in the band gap for instance we are very close to the valence band and the fact that you have localized electrons also is detrimental for the photo activity because these are very good trapping sites and so you increase recombination rates so the localization is negative for the properties of the material but only the right theory can describe proper reviews and this is another example because what I show you was delping with a transition metal in 2001 there has been an explosion of interest towards doping TIO2 with non-metal atoms like nitrogen and this was stimulated by a paper published in Science by Azai and co-workers the paper is now more than 9000 citations what they did they were talking of environmental photocatalysis not of fewer production but what they were showing is the following if you take TIO2 either pure TIO2 or nitrogen under UV light not visible light UV photons well it has a high efficiency in degradating pollutants however if you take visible light the normal TIO2 is non-active basically there is no conversion why the nitrogen doped TIO2 is very active because you start to saw photon of visible light beautiful they also provided a theoretical explanation of this and the explanation was based at that time to non-state of the art calculations but basically showing that you had this effect broadening of a band and the reduction of a band gap which would be fantastic that was the prediction well first of all let me mention that nitrogen doped TIO2 had been studied in 1986 by Sato but nobody realized that and he published exactly the same results 15 years before and this is the paper by Azayin Science going back to the distortions of modern science the paper of Sato never got cited until 2000 when this paper appeared somebody rediscovered that paper and that paper got cited 15 years after it was published but is essentially the same that was reported in the paper by Sato now why there is a what is the problem here let me open another issue this is TIO2 again the band gap is about 3.3 ev oxide semiconductors are never perfect you always have defects defects for instance vacancies, auction vacancies so they are very hard to be prepared in a fully stoichiometric way so what happens if you remove an oxygen atom from TIO2 the auction 2 minus remove an oxygen and the two electrons remains in the material and they are located in states which are close to the conduction band here more or less so high in the gap why this is relevant when you dope the material because you dope with nitrogen and nitrogen introduces a state which is close to the valence band so low in the gap and you have auction vacancies which introduce states high in the gap close to the conduction band so what happens naturally these electrons is transferred to this state and you form a new state which is doubly occupied notice that this is paramagnetic single electron this is diamagnetic why this is important ok, first of all the first message is when you dope a material there is a huge field you never have a single dope which introduces a single level there is a lot of possible interactions with others phenomena that occur in the same material in this case nitrogen doping for instance strongly favors the formation of auction vacancies because it lowers the cost of species and this was clearly demonstrated sometime ago with my colleague Elio Jamello in experimentalist in Torino because if you irradiate with samples with visible light you have diamagnetic centers because n with one extra electron is diamagnetic you excite electrons into the conduction band these electrons become active and you generate paramagnetic states which can be detected by APR now this study was very important because it demonstrated quite clearly that these states are completely localized are not delocalized contrary to the picture that was presented in science and since then we did a lot of systematic work on the various dopans that you can have in TiO2, boron carbon nitrogen fluorine and all the dopans introduce localized states so you may have a very stable state which are in the middle of the gap you reduce the absorption that is beautiful from the point of view of the absorption properties that is not so nice from the point of view of the recombination problems this doesn't mean that doping is useless there is a lot of work which is still being done on doping and codoping but of course let's move to another way of improving our activity hetero junctions Julio Czerulo has been talking yesterday about junction combining graphene with 2D materials and so on the idea is the same you can do it with semiconductors again is not a new idea I'm not sure this is the first paper Michael Grezzo proposed this in 1984 but the idea is very simple, you take two materials now, two semiconductors put them together and of course the idea is the following you excite one semiconductor you generate holes and electrons the electrons are where since you are in contact with another semiconductor, the electrons can move to this side on the other end you have this hole here which basically is filled and you generate and the hole moves in this direction so the electron moves on the left the hole moves on the right and you separate electrons and holes and separating the electrons and holes you avoid recombination this is a beautiful idea and of course it works partly there are various kind of hetero junctions it depends on the position of the levels but that is more technical and the idea which is even more sophisticated and which partly go back to the natural photosynthesis is to you take two semiconductors with different position of the band gaps but you put in between a chemical redox system what does it mean a chemical redox system you have one material where you basically generate the electrons and the electrons are consumed by these redox and you generate holes and the holes are used for your reaction on one side on the other side you generate the holes which are consumed by the redox couple and the electrons are used for the reaction on the opposite side again is engineering the system in such a way that you keep as far as possible electrons and holes to avoid recombination this is called Zetoski and so this is the general frame and now depending on how much time is left I will describe some practical results taken from our own work also to show you how things go when you go from theory to praxis I will discuss the case of basically mixing semi conducting or insulating like Syria with zirconia and zinc oxide there is an experimental part which is not my part I will mention that it is done again in the group of Edo Giammello but ok so in the first part I will show what happens if you mix serum dioxide with zirconia in the second part if you mix serum oxide with zinc oxide so we have the same component mixed with two different oxides notice that this is a wide gap zirconia is a gap of 5.5 EV zinc oxide is a wide gap semiconductor 3.4V so we are completely inactive in visible light ok so these are basically with two compounds but the preparation of the first compound is done by solgel solgel is a chemical way of producing new materials and of course you start the synthesis and you don't know exactly what you obtain and in order to know what you obtain you have to do a number of characterizations and here what happens this is an extradi fraction pattern it shows very clearly that in this synthesis serum is entering as a dopant in zirconium dioxide so it is diluted as a dopant you don't have segregation of different materials well you have produced a new material and now the first thing he wants to do is to see what is the activity or what is the activity in under visible light as I told you prist in pure zirconium dioxide is a gap of 5 EV will never absorb visible light photons however if you dope with serium this is the absorption of pure zirconium no absorption in visible light if you have serium doping 1, 2, 5% you start to absorb light in the visible light region ok, that's already interesting it doesn't say much you have to see what is visible light doing and you can do this again using electron spin resonance because using electron spin resonance to make the story short you take the spectrum the different spectrum before and after irradiation and you see that under visible light visible light not UV light, you generate holes and electrons so clearly you are exciting electrons or valence band to the conduction band of the material not only this but if you now look at what happens at the surface of the nanoparticle you can react molecules like oxygen electrons are trapped by oxygen you form O2- and O2- is again can be seen in electron spin resonance which means that the electrons and holes are generated in the nanoparticles they migrate and they reach the surface and at the surface they can react both the electrons and also the holes through a more complicated mechanism but you can detect the formation of holes so the message here is yes you take a material which has no absorption visible light and it becomes active invisible light and the electrons and holes are generated and reach the surface now what is the mechanism we are not yet completely sure about what can be the mechanism what theory tells you that we do calculations is that yes, you have a wide gap insulator but the Syrian dopant introduces new states in the middle of the gap and these new states can act to some extent as in intermediate positions where you can have double excitations you can excite first to these levels and then from these levels to the conduction bed it is not so easy now I don't want to open how to compute excitations in solids which is not a trivial task but here we did it for the people of the experts in the audience using the so-called transition charge transition levels but finally we compute the transitions which are 2.5 and 3.1 which are compatible with visible light absorption in particular if you take into account that you have an overestimate of a bang gap of about 15 percent so the message is of this first part here doping in purity atoms Syrian replacing zirconium in new states in the gap and a material which has no visible light activity become active in visible light now let's take the second example which is again Syrian oxide mixed with zinc oxide the synthesis is again solgel so it is basically the same you start from precursors and so on interestingly enough the final compound that you get is completely different there is no longer serium diluted into zinc oxide but very clearly the synthesis has produced small aggregates of seriodioxide so nanoparticles of seriodioxide on nanoparticles of zinc oxide so there is a natural junction and this depends on the synthesis and is very difficult to know a priori what you are going to get but this is quite clear there are a number of measures showing this formation of two separate phases seriodioxide and zinc oxide however interesting enough also this material becomes slightly active in visible light in sort visible light more than pristine material but more important under visible light again you can follow the generation of species, holes and in this case zinc plus ions, electrons in the conduction bed again using visible light so zinc oxide has no absorption in the visible by mixing or creating a natural junction you make the material active in visible light and why again here theory can produce some answer here what we did we constructed a model of the junction which is not the trivial thing because when you have two materials of course you have strain you must have lattice constants of the two phases which match together nobody really knows what is at the interface how the interface is done and so you have to create a model and hope it is close to reality because it's not so obvious so we started this hetero junction and we computed the lowest excitation the lowest excitation turns out to be much lower than in the two separate materials and the reason is that now you excite from one component, from zinc oxide from the valence band where you generate an O minus you excite into the other component and you generate a serium 3 plus at the interface and this excitation starts at the interface at much lower energy than in the bulk materials when they are taken separately ok, again this shows that these electrons and ores in the real material they reach the surface they interact with molecules on the surface so they produce photo catalytic processes and in fact this material has been shown to be very active in the degradation of pollutants under visible light ok, this is basically the summary or basically what I wanted to show you that you can take you can modify semiconductors the what you get is largely determined by the synthetic procedure and it's very difficult to know a priori what is going to happen but I show two examples where you can end up with a real doping case I think still there is a lot of work to be done in this field which however is quite exciting and I would like to thank my co-workers and in particular my experimental co-workers for the part of the talk that I've shown to you thank you very much for your attention