Dear Sir,

maybe you should think again about the screening argument. In complete spin polarized electron energy loss spectroscopy (CSPEELS), Fromme et al. have observed distinct 4f-4f crystal field transitions in EuO(001) single crystals, i.e. the crystal field has a distinct impact on energy levels. For details see

DOI: http://dx.doi.org/10.1103/PhysRevB.64.125114

Sincerely, FM

The answer is based upon the following two well established concepts:

[i]The occurrence LMCT in RE compounds and the transfer of this energy to the neighbouring RE ion to cause excitation of the neighbouring RE is a well reported concept.

[ii]No transfer of energy is permitted between the RE ion and a non RE/Transition ion.

Considering these two points ,there occurs LMCT in between Eu^2-Y^3 while no LMCT phenomenon occurs in between Eu^2-Ca^2.

So ground state energies of Eu^2 in YPO4 and that in CaF2 are expected to differ.

For transition metals the crystal field (typically 5,000-30000 cm-1) is much larger than the spin-orbit coupling (Delta < 1000 cm-1) so we consider the effect of the crystal/ligand field first (which removes the degeneracy of the d orbitals) then we apply a perturbation to take into account spin-orbit coupling; for A and E terms this is a second order effect but for transition metals with T terms the spin orbit coupling is a first order effect and couples the residual L(eff) to the spin S to give J(eff) values. These give rise to (I) temperature dependent magnetism and (ii) fine structure associated with the different J(eff) states arising from spin-orbit coupling.

For lanthanides the spin orbit coupling (which depends upon the atomic number Z^4) is large (1000 cm-1 or so) whilst the crystal field effects are small (Delta maybe 100 cm-1 or so). So, at undergraduate level, for lanthanides the crystal field effect is ignored and we consider only spin-orbit coupling. For magnetism, for most lanthanides the room temperature moment corresponds closely to that we expect for the free ion ground term since lambda >> kT. However there is a small crystal field and if we include the effect of the crystal field on the ground term (and the excited state terms) then the J ground state splits, leading to fine structure in the spectroscopic properties. The nature of the splitting reflects the local symmetry of the lanthanide ion.

Thank you very much for the valuable suggestions.

To determine the position of 4f ground state energy of Eu2+ ions in the different compounds, the usual way is to utilize the charge transfer energy (CT band)of Eu3+ in the same host. I found myself a mistake understanding about the fact. The CT energy equals to the energy from the top of the valence band to the ground state of Eu2+, but not the real energy of the ground state of Eu2+ ions in the compound. So, if we did not take the spin-orbit coupling of 4f states into consideration, the real energy of 4f ground state energy of Eu2+ should be the same in the different host. I believe that the different CT band energy is due to the binding energy of anion ions differ in the various compounds, which composed the top of valence band. The nature of the transition from the valence band to conduction band, as well the transition from the valence band to the 4f state of Eu3+ ions is the same, and the binding energy affects a lot.

Dear Yongchao Jia,

If your good self have carefully gone through my humble answer,

your self woud have certainly found it what you are yourself proposing now.

But, I, very humbly ,add to your answer. The term CT needs to be qualified- whether LMCT( Ligand to Metal Charge Transfer) or MLCT(Metal to Ligand Charge Transfer) and why?

Here it is LMCT and not MLCT and that too only in Eu^2-Y^3 and not in Eu^2-Ca^2.

So a part is still left unanswered- why LMCT& not MLCT?And why only in in Eu^2-Y^3 and not in Eu^2-Ca^2? For this explanation , more is needed but available in the literature in abundance.

Good luck.

Dear Dr. Jeremy Rawson ,

Feeling honored to engage myself briefly in an academic discussion with a person of your excellence, your exalted point of view holds good for explanation of large difference in theoretical & experimental magnetic moment values of Eu^2,3 complexes where the various J components are comparable to kT in their energies to make some contribution in their magnetic moments from the successive J components in addition to the ground J component( The formula applied to Large Multiple Width is not applicable). But the said query pertains to the difference in energy brought about by in the ground J component by the neighboring Ca^2/ Y^3 ions. Regards.

Dear Mr. Sehgal,

I appreciate that you can have an interest to the question.

In my opinion, the CT band of trivalent lanthanide ions, Eu3+ ions, in the simple compounds,such as the oxides and fluorides, is the electron transition between the the surrounding anion ions to the Eu3+ ions. For example, the electron transition from O2- to Eu3+ in the Y2O3, and the corresponding transition from F- to Eu3+ in the YF3.

I cannot understand CT transition between Eu2+-Y3+, as you mentioned, would you like give me some references? I did not the reverent information in the google site.

Best Wishes,

Yongchao

[A]Normally, Eu(II)[4f^7] is not expected to undergo CT, yet with its various J components having energy difference comparable to kT,it MAY undergo CT if its neighbouring RE ions have their ground states energies less than the energy of ^8S7/2 of Eu(II)

[B] Pls. find below a few examples where Eu(II) does show CT in in Y(III) as well as other ions:

[I]DISSOCIATION OF THE Eu+2 CHARGE-TRANSFER STATE INTO Eu+2AND A FREE HOLE IN Y AND La OXYSULFIDES

Struck, C. W.; Fonger, W. H.

[II]Charge-Transfer Luminescence and Energy Transfer in Eu2+-Doped Barium Zirconosilicates

1. De-Yin Wanga, Ling-Li Wangb, Te-Ju Leea, Teng-Ming Chena,z and

2. Bing-Ming Chengc

ECS - The Electrochemical Society

0013-4651/2011/158(12)/J377/6/

[III]Journal of Photochemistry & Photobiology, A: Chemistry

2014 | 274 | Complete | 64-72

Photoinduced electron transfer from Eu(II)-complexes to organic molecules: Rate and mechanistic investigation

Sandeepan Maity Edamana Prasad

[IV]Radiation Effects and Defects in Solids: Incorporating Plasma Science and Plasma Technology

Volume 158, Issue 1-6, 2003

Charge-Transfer Processes in Doped Alkali Halides

V. Babina, A. Krasnikova & S. Zazubovicha*

pages 227-230

Published online: 14 Mar 2014

•

Thank you very much for providing such information, Mr.Sehgal.