 Hello everyone and welcome back to the series of lectures on actinide chemistry. In the last lecture we have left on the studies that is the different studies of lengthenites and actinide. And in this particular table I have given you the lambda max as well as the epsilon max that is the molar absorptivity of different actinides in one molar per crudic acid. And you can see that many of the actinides is having very high E max but suggest that you can measure even very small quantity of these actinides using UVV spectroscopy. And in application part we have already discussed what are the kind of applications you can think of using abrasion spectra. The first one is like quantitative analysis. You just want to have an idea of the obstetrician state. You can also do some quantitative analysis provided the medium in which you want to do the quantitative analysis you should be having epsilon in that particular media. So if you are knowing that epsilon values you can do some kind of quantitative analysis also. I have given you some example of the redox selection also where I have shown you that one can study the kinetics of the redox selection using UVV spectroscopy and the complexion of metal ion using different ligands as we seen in the previous slides that once these ions make a complex with the different kind of ligand under given set of conditions their abrasion spectra will change. And based on that changes if you do a titration that I have shown in the figure here in which I have shown you that if someone start with some concentration of nephrinum and do the titration with some ligand there is a shift of the P that occurs at around 976 to 991. And if one does the titration then by fitting the titration data into there are certain software that comes for that and you can fit the data and the it is simply based on the dampened weight law and you can get an idea about the stability constant of this complex just by using this spectrophotometric titration. You can also get estimation of the lanthanides and actinides that are present in the environmental sample in a very small quantity. In cases when the quantity is so small then we generally prefer to use some kind of chromophilic reagents which again having very high Charon value and because of their very high Charon value you can go to a very low concentration. With that we will move to the other spectroscopy that is called emission spectroscopy. So there are certain terms that you may be familiar with but I will just give a brief note on these different terminologies. The first one is absorption as we have already discussed that what I mean by the absorption spectra and the next term is like excitation. So does the excitation spectra and the absorption spectra are same? The answer is not exactly because let us assume that you have a species, you have a species which has a spectra absorption that is the A. In your absorption spectra you are exciting with certain wavelength of the light so you are getting this kind of spectra wavelength versus your intensity or your absorbance of suppose some species A but in your excitation spectra when we read that how to record the excitation spectra then you will find that whatever peaks are coming for the absorption spectra may not be coming exactly same for the excitation spectra. That we will see in the coming slides that how the excitation spectra is recorded and once you know how the excitation spectra is recorded you can very well understand that why there is difference between the absorption spectra and excitation spectra. You can see that emission spectra is again if you see the simple Javelin's diagram here we know that absorption starts from ground state to any one state that is can be like some singlet 1, singlet 2 and there with the viagronic relaxation it comes back to the ground state of the first excitation state and from there they can either go by intersystem portion to the triplet or they can come back and this kind of coming back generally if it is a relative process it will emit some kind of radiation which has already recorded and if they are falling in the reason that is visual reason then we say it is a luminescence and depending on the time at which the decay is taking place it can be a fluorescence which is having very short period of time after excitation whereas if the time is long basically in those cases it is going from singlet to triplet and from there it is coming back in those cases generally it is first fluorescence which is called sometime delayed fluorescence also so I hope you have these terms in your previous classes so you can better understand them with that we can just see that what are the sources that one can use for the emission spectroscopy so here I am giving you the basic setup in a normal photometer one would have an excitation source and then obviously out of certain bunch of radiations you select one for your excitation and then you put your sample there is radiation will excite your analyte from the ground state to the some state of singlet and then from biometric relocation they will come here and then from there they will emit but you see that here if you see the geometry you find that my detector is kept 90 degree to the sample number why it is because this intensity is too large so if you are keeping detector here and whereas the emission signals are very very weak so if you are keeping detector in this reason you will be only recording the excitation source spectra you will not be able to get emission profiles so for that reason to avoid this intensity from the source we use to put the emission detectors at 90 degree and from there you select the emission thermometer you record the emission spectra and you get spectra so depending on the excitation sources as I showed you that you have to excite first you have to excite your molecule from the ground state to the excited state so depending on the excitation source you can have different kind of luminescence just such as some of them have given like cathodoluminescence in which one use the electron beam as an excitation source or X-ray or a particle if you use this kind of sources for your excitation they are called radio luminescence if you are using electric field then it is electro luminescence so depending on the nature of your source that you are using for the excitation you can have a variety of luminescence is starting from a cathodoluminescence to thermoluminescence and in this particular we are mainly interested in photoluminescence where we are using a photon or you can say the light source as a excitation so when we have this excitation or you excite with some photons then what kind of information that we can get so again you excite and then from the ground state of the excitation still it is emitting so what kind of spectra we can record we can record something that is called excitation spectra we can record emission spectra beside that we can also record lifetime and so this techniques give you triple resolution one you can have some information from the excitation you can have some information from the emission spectra and you can have an added information from the lifetime also and this generally has very high to signal noise ratio and many a time it is a non-invasive and non-destructive technique so what we can do and how we are doing that we will try to see in the next slide so if you talk about the lanthanides and actinides so as we see that in the lanthanide the energy level are quite far away as compared to the actinides or rather you can see the actinide poses a ladder-like pathways so what happens because of this ladder-like pathways in the actinides when you are exciting from the ground state to any upper state then most of the photons come back to the ground state just by a non-invasive process so they are not fluorescent or many of the actinides you will not get any fluorescent whereas in case of lanthanide this kind of ladder-like pathways are missing and because of that we can see most of the lanthanides give very good luminescence and actinide you are having luminescence mainly from amyricium, curium and uranium and for others although they can give you some sort of emission line but they are lying in the NIR region so we can say that they are fluorescence so in fluorescence reason we are mainly getting three that is amyricium, curium and uranium because these are the one who is emitting in the region that is the visible region we have already discussed about the term symbol so I'm not going into the details but I just want to add that since we are going to study about the luminescence and here I'm using a European as a example so I just want to have a look on the states that European do have and as we have discussed that with the F6 configuration of European 3 class we are having a 7f state and in 7f state we are having certain J levels and those levels are 7f, F02, 7f6 and we have also seen that out of these levels which is the ground state though 7f0 is the ground state and 7f6 is the highest state in this 7f level so let us understand first that okay how one record the excitation spectra or the emission spectra before going to study the detail about the European spectra so here I have given you some of the emission spectra of different lengthenites and you can see that many of the lengthenites do emit in the region that is visible region you can see this region or this region so they emit and some of them basically emit in an higher region also so most of the colored compound are generally emitting in this region as you can see here also that European is generally reddish color so that is coming from its emission most of the compound of European and terbium is again green so you can see the emission is in the green region so first thing I would like to tell you that how we record this kind of spectra as if you want you that you have a source then since we are doing a photoluminescence our source is 0 in length in this case and then depending on your metal ion suppose I am using European so depending on your metal ion you put a monochromator and you choose certain wavelength so for a European which was wavelength if around three ninety four nanometer if you remember then in the absorption spectra of European I have shown you that this transition that is happening the earth 94 is basically starting from 7 and 0 and go up to 5 and 6 so this is the transition that is happening place earth 94 so we are using this transition for the excitation and once you excite then there is obviously some emission spectra so what we are doing to recording for the emission spectra we want to record the emission spectra and what we are doing we are first fixing the extraction wavelength in this case I fix at 94 nanometer and then I excite and I scan the emission monochromator to get emission spectra and then I get certain lines here so this is the intensity and this is the emission time we get for emission spectra we are fixing the excitation wavelength similarly if I want to record the excitation spectra here I will also tell you about the difference that you can understand the absorption spectra and excitation spectra so suppose I want to record an excitation spectra I want to scan the excitation wavelength first I have to fix the emission wavelength for Europeans that is say we have fixed it at certain value now that will happen we have fixed this path what does it mean that suppose you excite a certain wavelength you can only see peaks in the excitation spectra when you are seeing emission here suppose I have three peaks in the absorption spectra in the UV reserve spectra but even after excitation using this peak I am not having any emission at 6 square I will not see this in the my excitation spectra now I will try to excite at this suppose you are exciting in this region and you are able to get some peak then you will see that so only those peaks are visible in the excitation spectra which keep luminescence at whatever fixed wavelength you have chosen so in absorption spectra you may get more than one lines but it doesn't mean that all those lines are giving you the emission profile so by fixing the emission at a given wavelength when we scan the excitation monofilometer we are getting some excitation spectra now we are having excitation spectra and we are having emission spectra let us say that we are having excitation spectra of kind this is of my emission spectra in which we are getting a peak here and again we are having an so this is of my emission spectra and again we are having some excitation spectra in which I am getting peak at 394 millimeter so now I am having an emission spectra I am having an excitation spectra what I will do I will choose the peak maximum whatever is getting the emission spectra and the peak maximum whatever I am getting in the excitation spectrum and these two positions I am using to find out my lifetime data so what I am doing in the lifetime data I am using excitation source at 394 emission line at 612 and both I am fixing before recording the lifetime spectroscopy so by fixing these we record the lifetime so this is the way we record these three kind of spectra that is the excitation spectra emission spectra and the lifetime spectra and what are the kind of information that we can get from this kind of spectra we will discuss in the next slide and here also I have just shown you that different ground shift term symbol that you have derived using the term symbol recipe that I have given in the last lecture so you can easily follow that and you can try most of this term symbol using that recipe so now since I told you that we will discuss about the european but before going to the discussion I will just show you certain important things that one should be able to understand before plotting or before recording any kind of emission spectra the first thing is you should be having a knowledge of the different kind of levels you should know that what is the ground state what is the first state what is the second state this information we should be having and when you are exciting then before the excitation the first question comes at what wavelength because if you given a sample you don't know what is the wavelength at which I have to excite then what to do you can take help of your absorption spectroscopy and as I have shown you that in your absorption spectroscopy you may be having more than one peak you have to try at different peaks and you have to try at different excitation wavelength and then you scan the emission and at whatever wavelength you are getting good emission you can say okay okay this is the excitation wavelength for this particular metal ion but how to write the transition suppose I write that I am exciting from here suppose this is my ground state that is a 7 of 0 and I am exciting I am going to let us say here as I said that we go to 5L6 and take some steps suppose I am going so how to write so there is a way to write that we can write like 7 of 0 to let us say 5L6 or we can also write 5L6 and then we can put a arrow like this and we can write 7 of 0 so what is the right way of writing how do we represent this transition that okay this is my absorption transition and this is my emission transition the rule is that whenever you want to write either you want to write an absorption transition or any emission transition you should always take care that your high energy state should be always at left hand side and your low energy state is on the right hand side but it means that if you see this notation my high energy state my 5dg euro is high energy state my high energy state is on the right side which is wrong your low energy state should be on the right hand side so this notation is wrong so what we have to do we have to always keep this in mind that whenever we are writing my low energy state should be on the right hand side so what is my low energy state here my low energy state here is suppose 7 of 0 so this is my low energy state this should be on the right hand side and my high energy state suppose I am doing some 5d0 this should be on the left hand side and when I am doing any kind of absorption since it is my lower state I have to write like this suppose I want to write about the emissions then these things you have to write like this only that your low energy state is on the right side but since you are talking about emission yeah that's right like this so only the sign only the arrow will change this state's position will not change so even the recent literature have seen lots of people do not follow this notation but I think it is a good habit that if you start following this habit that whenever you are writing it should be cautious that always your low energy state should be on the right hand side one more thing that many time whenever we are plotting we use wave number or sometime wavelength but in general convention one should plot always in wave number scale with the highest wave number on the left hand side and the lowest wave number on the right hand side of the spectrum so this is a very typical spectrum of the European that I have given here if you see that it has several lines that arises from the transition from 5d0 to different state that 7f0s to 7f1, 7f2 so all these transitions so you can see from this diagram very well you have excited from 7f0 to 5f6 so you have excited to 5f6 now they are emitting their emission is taking from 5d0 so when they are emitting you are getting a peak that is from 5d0 to 7f0 the generally we should see that it is a kind of 0 0 peak then 7f1, 7f2 so like that you start from 5d0 and you are getting all these peaks that is 7f0, 7f1, 7f2 so when we are getting these peaks what does they mean what you can understand that these peaks are coming from the ff transitions right so you can have some idea about the energy levels of the metal line of the atom you are probing you can also see that when we are moving from the 7f0 to the 7f4 states you can see the distance between the Js and Js plus one line if I say the distance between f0 and f1 line if you see the distance between this f0 and f1 line they are very close to each other but the moment you go for higher so when I say higher means suppose you are instead of like 5d0 to 7f0 now you are seeing distance between 5d0 to 7f6 and 5d0 to 7f5 transition so when you are measuring at the higher J value you are finding that the distance between the two J lines are increasing this is coming from the land-interval rule that the interval is increasing as we are going from the left hand side to the right hand side or you can see the splitting has increased when we are moving towards the higher J values and this transition that we are getting in the luminescence they are mainly known as induced electric dipole transition and their origin is mainly due to the interaction of the lanthanide with the electric field vector through the electric dipoles of the electromagnetic radiations and when you talk about this transition they are again laboratory forbidden so their intensity is also not very good but still you see that because of certain intermixing of the different state since these are laboratory forbidden and they are very weak so this is called induced electric dipole transition but one more transition that you can see is called migrant dipole transitions these transitions are largely independent of the environment of the lanthanide ion and sometime they are also using internal reference for your spectra these are some of the selections rule that is given for electric dipole, magnetic dipole as well as induced electric dipole transition and as I told you that all these transitions are of not same nature some of them are electric dipole and some of them are magnetic dipole and here I have just given you the list that if you see that the transition that is 5D0 to 7F0 so if you see this emission line from 5D0 to 7F0 this is electric dipole but the second one that is a 5D0 to 7F1 that is a magnetic dipole when I say magnetic dipole it means its intensity do not have very much variation when we are changing the ligand field and rest of the you can see these are electric dipole transition so many a times this transition that is 5D0 to 7F1 are used as an internal standard when we are trying to compare different systems of same ion and we will try to understand what is the ligand strength and how the ligand is doing splitting and what ligand is doing what kind of splitting so sometime we use this kind of magnetic dipole transitions for understanding of the ligand or the symmetry around the metal ion these are some of the selection rules that is generally comes from the quantum mechanical calculation that what kind of transitions are allowed and what kind of transitions are forbidden using this set of rules that are called selection rules and depending on the selection rule those transitions who follow the selection rule they are intense whereas those transitions who do not follow the selection rule they are either they do not happen or if there is some intermixing between the different F states they have certain probability of happening and because of that they get some intensity but again it is a very poor intensity so we will not discuss about the application of emission spectra once you have the emission spectra recorded what are the kind of information that you can draw from the emission spectra the first information you can easily draw whether you have different complexes or the same complexes when I say different complex or the same complex my metal center is same when I say different I mean the symmetry around the metal ion suppose you are having a complex let us say european with three different ligand that is l1 l2 and l3 but you can see directly from this figure that although they are having european in the center but the peak intensities and the splitting and the pattern is quite different from each other so just by looking at this spectrum what information you can directly drive is that the symmetry around european ion in the three system are different so this is the direct information we can get suppose you want to have information about the stability then you can take any one system and as we are doing titrations in the emission spectra you can do some sort of titration here also and from the titration data you will get the stability constant of that particular complex so this can also be used for the conclusion of the stability constant you can also use this kind of spectroscopy for the detection of lanthanide and actinide in the environmental sample and detection of uranium in various kind of environmental sample using laser photometry which is a kind of emission technology technique is very common so this is also used for the understanding of symmetry as well as for the quantification of the metal ion into the environmental samples they can also tell you about the symmetry exact symmetry around the metal ion as i said that you can see the symmetry is different but what is the symmetry that you can tell using this emission spectra that will come in the next slide but before that as i told you that you have certain peaks and out of those peaks the peak at 7 at 1 is magnetic dipole rest others are electric dipole so if you take the ratio if you take the ratio of the magnetic tribal transition to the electric dipole transition you will get something that is called asymmetry ratio and this asymmetry ratio is very important when you want to understand the symmetry around the european ion it so happens that this ratio is very high when the symmetry is very low and the ratio is low when the symmetry is high for example in water where the symmetry is very high this ratio is around 0.5 to 0.6 so this asymmetry ratio can be used to understand at least to say that whether the symmetry is high or the symmetry is low but what is the exact symmetry to get that information we have to look this table so as we have known that when we are having some states let us say 7f0 or 7f1 or 7f2 any state that we are having any term symbol so we have seen that okay these are getting split because of ls coupling but what about this state they further get splitted because of the jj coupling and what we get the splitting is nothing but 2j plus one so you can say the 7f1 can split into 2j plus one means like three another state so that is 7f plus one zero and minus one so you can say that all the j states can further split depending on the field around them depending on the electric field around them so from this splitting pattern that we get in the j we can understand what is the exact symmetry class of that particular metal ion or what is the symmetry around that particular metal ion one thing you have to take care that you can just tell about the symmetry class which you may not be able to tell you about the exact point group what belongs to because for a given point group the splitting pattern is identical so you may not be able to get exactly whether it is d4h d4v but you can certainly say that yes when we have certain splitting suppose you are having this splitting that the first peak is mono splitted and this is the 2 and this is 4 so you are having this kind of splitting pattern you can definitely tell yes the european is having a tetragonal environment but exactly this d4h and d4v it is not that easy to tell but people try to tell that using studies at low temperature but that require a lot of experience and it's not that straightforward but you can at least have an idea about the class symmetry class using just by looking at the splitting of the j level so here i have given some example that how they look like so suppose you have splitting in this 7f2 level here you can say the maximum is 5 and to get maximum you should be having symmetry in the trichlyonic region where you can say that 7f2 should be 5 so the more unsymmetric the environment more is the jj splitting so trichlyonic is the less asymmetric or the most asymmetric so we are getting 5 peaks here and you can say 7f1 which has maximum jj splitting of 3 you are getting 3 peaks so like that if you are doing studies at a very low temperature you can get these fine splittings and from this number of fine splitting of different j levels you can get information about the class the symmetry class of european man that what is the symmetry around the european man in this particular complexes we have also studied about the hydration of european man and there we have seen that deluminescence purpose can also be used to find out the number of water molecule into the primary hydration sphere and for that one needs to measure something called decay last time and i've shown you that for measuring this decay half-life and decay time you have to excite at certain wavelength and then you have to measure emission at a certain wavelength and that should be done at a given wavelength at given excitation wavelength at given emission wavelength so once you have a certain wavelength let us say for european the excitation at around 394 and emission at 612 you'll get some kind of curve like this which you follow with time once you get this kind of curve what we have to do you have to just fit this curve using a mono exponential decay line time so what is that decay you have curve that is intensity here intensity and time is here you are measuring time suppose in millisecond or microsecond so if the curve is like you have a exponential to the power minus t that is your x axis into decay constant that is so the equation is like a exponential minus t that is the time on the x axis into your decay constant that will give you the intensity this is for the mono exponential similarly we can write for the bi exponential or the right exponential and from there you can get information about k obs that is the decay observed decay constant and from this observed decay constant you can have idea about the number of water molecule in the primary sphere how we can get that idea because we are having certain little relationships so suppose you take about european we are having a relationship between number of primary hydration sphere water in the primary hydration sphere and your observed decay constant here you have to take care that all these values are given in millisecond so suppose you have a lifetime of 100 microsecond so before using this application before using this equation you have to convert this microsecond to the millisecond so you have to convert that before using this equation and once you do that you can put the equation in this and for 100 microsecond you will be getting around 8 to 9 monotone molecule so directly using this relationship and the knowledge of decay constant you can get the idea about the number of water molecule in the primary hydration sphere the graph here shows that the variation in the primary hydration sphere number of water molecule in the primary hydration sphere with the ph where you are titrating a given metal ion here the metal ion taken is the curium so suppose you have curium and you are titrating you have added some ligand any ligand you can choose here suppose you have added that ligand into the system and now you are wearing the ph what will happen that when the ligand when you are wearing the ph a ph will come when the ligand is more and more deprotonated and the moment is deprotonated what will happen suppose curium is having 8 water molecules here around them and your ligand is deprotonated and it has two sides so now it can attach to the metal ion and it can remove two water molecules and since it is removing two water molecule so whatever is there in your aqua complex you will get a decrease of two water molecule so depending on the nature of ligand that can happen at a different ph for example in the first two ligands you can see that even at ph2 the complexation is stored strong that almost all the water molecules have been removed whereas for certain other other complexes such as NTFC and lutein acetic acid this is not that straightforward so it is a stepwise removal of the water molecule so just by doing the lifetime spectroscopy you will get this kind of information in changing number of primary water molecule using different ligand in a set of ph conditions and this table is also showing with that for a given ligand depending on the statutory material of the metal ligand complex how many water molecules are possible so suppose I give you a ligand that is again nitro nitro triacetic acid and I assume that it has a stratumetry of 1.1 so if you have a stratumetry of 1.1 how many water molecules should be there in the primary sphere and you can just follow the equation that is given on the top that from this you can always get the information about the number of primary water molecule into the metal adhesion sphere so with that I would like to end thank you thank you very much for listening