Determining binding energies of valence-band electrons in insulators and semiconductors via lanthanide spectroscopy

Abstract

Models and methods to determine the absolute binding energy of 4f -shell electrons in lanthanide dopants will be combined with data on the energy of electron transfer from the valence band to a lanthanide dopant. This work will show that it provides a powerful tool to determine the absolute binding energy of valence band electrons throughout the entire family of insulator and semiconductor compounds. The tool will be applied to 28 fluoride, oxide, and nitride compounds providing the work function and electron affinity together with the location of the energy levels of all divalent and all trivalent lanthanide dopants with an accuracy that surpasses that of traditional methods like photoelectron spectroscopy. The 28 compounds were selected to demonstrate how work function and electron affinity change with composition and structure, and how electronic structure affects the optical properties of the lanthanide dopants. Data covering more than 1000 different halide (F, Cl, Br, I), chalcogenide (O, S, Se), and nitride compounds are available in the archival literature enabling us to routinely establish work function and electron affinity for this much wider collection of compounds.

Luminescence spectroscopy and energy level location of lanthanide ions doped in La(PO3)3

“…7. The energy difference E VC between the top of the valence band at E V and the bottom of the conduction band at E C is taken 8% larger than the exciton creation energy E ex ¼ 8.45 eV in order to account for the estimated exciton binding energy [18]. E CT defines the energy difference between E V and the ground state energy E 4f (7,2þ,A) of Eu 2 þ .…”

“…Such scheme provides a new method for the visualization of the location of the relevant lanthanide states with respect to each other and to the bands of the host compound. The first VRBE schemes were constructed for fluorides, aluminates, nitride compounds [18] and also already presented for some oxide materials [19][20][21].…”

The Electronic Structure of Lanthanide Impurities in TiO2, ZnO, SnO2, and Related Compounds

“…In the case of TiO 2 , bondlengths around a lanthanide on those sites will be smaller too resulting in smaller centroid energy and U (6, A). We therefore estimate for TiO 2 and ZnO U (6, A) ≈ 6.7 eV and for SnO 2 with the larger value for χ U (6, A) ≈ 6.8 eV. Figure 1 shows the VRBE for all lanthanide states when a value of 6.7 eV is used for U (6, A).…”

“…and full consistency with available experimental data from different fields of science was demonstrated. [2][3][4] It was found that in inorganic compounds based on rare earth cations, like YPO 4 and LaBO 3 , and/or alkaline and/or alkaline earth cations like CaF 2 and CaGa 2 S 4 , the binding energy at the bottom of the conduction band E C is typically near −2 eV. Sc-based compounds like ScBO 3 and ScPO 4 tend to show lower values for E C which was attributed to a large binding energy of electrons in the 3d-shell of Sc 3+ /Sc 2+ that forms the bottom of the conduction band.…”

“…By using spectroscopic data for different lanthanides like Ce 3+ , Pr 3+ , Tb 3+ , Eu 3+ , Yb 3+ in the same compound, the model enables to derive the electronic structure with the absolute electron binding energies, i.e., relative to the energy of the electron at rest in vacuum, in all divalent and all trivalent lanthanides. 2 It has been applied to about 50 different compounds (fluorides, chlorides, aluminates, phosphates, borates etc.) and full consistency with available experimental data from different fields of science was demonstrated.…”