Energy levels in CaWO4:Tb(3+) at high pressure
S Mahlik1, E Cavalli2, M Amer3
1Institute of Experimental Physics, University of Gdańsk, WitaStwosza 57, 80-952 Gdańsk, Poland. s.mahlik@ug.edu.pl.
Abstract:
The luminescence properties of Tb(3+) in CaWO4 crystals are investigated under a hydrostatic pressure of up to 200 kbar, i.e. across scheelite-to-fergusonite phase transition. It is shown that the typical blue ((5)D3) and green ((5)D4) emissions in this material are progressively quenched at room temperature as pressure is increased. This quenching is caused by a downshift of the charge transfer (or impurity trapped exciton) state that is formed between Tb(3+) and nearby W(6+) cations in conjunction with a pressure-induced increase of the lattice relaxation experienced by this excited state. An empirical model is introduced to calculate the evolution of the (Tb(3+)-W(6+)) charge transfer energy with pressure. Combined with the pressure dependence of the energy bandgap in CaWO4, the model allows locating the 4f levels of Tb(3+) relative to the fundamental host lattice for any pressure in the range 0-200 kbar.
Related Concept Videos
02:58Crystal Field Theory - Octahedral Complexes
To explain the observed behavior of transition metal complexes (such as colors), a model involving electrostatic interactions between the electrons from the ligands and the electrons in the unhybridized d orbitals of the central metal atom has been developed. This electrostatic model is crystal field theory (CFT). It helps to understand, interpret, and predict the colors, magnetic behavior, and some structures of coordination compounds of transition metals.
CFT focuses on...
03:02Colors and Magnetism
When atoms or molecules absorb light at the proper frequency, their electrons are excited to higher-energy orbitals. For many main group atoms and molecules, the absorbed photons are in the ultraviolet range of the electromagnetic spectrum, which cannot be detected by the human eye. For coordination compounds, the energy difference between the d orbitals often allows photons in the visible range to be absorbed and emitted, which is seen as colors by the human...
02:46Crystal Field Theory - Tetrahedral and Square Planar Complexes
Crystal field theory (CFT) is applicable to molecules in geometries other than octahedral. In octahedral complexes, the lobes of the dx2−y2 and dz2 orbitals point directly at the ligands. For tetrahedral complexes, the d orbitals remain in place, but with only four ligands located between the axes. None of the orbitals points directly at the tetrahedral ligands. However, the dx2−y2 and dz2 orbitals (along the Cartesian axes) overlap with the ligands less than the dxy,...
02:42Valence Bond Theory
01:19Phase Diagram
01:01Energy Bands in Solids
Band Formation:
When atoms are brought close together, as in a solid, these discrete energy levels begin to split due to the overlap of electron orbitals from adjacent atoms. This split occurs because of the Pauli exclusion principle, which states...