Electronic Structures and Host Excitation of LaPO₄, La₂O₃, and AlPO₄

Abstract

We report the electronic structures and associated optical properties of three inorganic oxides, namely lanthanum oxide, aluminum phosphate, and lanthanum phosphate, calculated by the first principles augmented spherical wave (ASW) and full potential linear muffin tin orbital (FP-LMTO) band structure methods, and the self-consistent field Xα scattered wave (Xα SW) molecular orbital cluster approach. Our calculations indicate negligible effect of the choice of exchange correlation potentials on the position, shape, and relative ordering of the energy bands. The ASW energy gaps in lanthanum phosphate and aluminum phosphate agree satisfactorily with the measured values. A comparison of the electronic density of states for an isolated phosphate group from molecular orbital calculation and that of the valance band from the band structure methods indicates that the nature of bonding within the phosphate groups does not change in aluminum and lanthanum phosphates. The states near the top of the valence band and bottom of the conduction band are mostly due to the phosphate bonding and antibonding orbitals, indicating that optical absorption near the band edge involves excitation of electrons from the bonding levels to antibonding levels associated with phosphate groups. This explains why the optical gaps in many rare earth phosphates are nearly equal.

XPS surface analyses of LaPO4 ceramics prepared by precipitation with or without excess of PO43−

“…A binding energy of 3-4 eV for this state is in good agreement with preliminary density of state (DOS) calculations done by us, DOS calculations reported by Mishra et al 7 and qualitatively with features observed in the rather crude XPS valence-band spectra that we have been able to obtain at the present stage (Fig. 4).…”

Electronic, structural, and optical properties of host materials for inorganic phosphors

“…The most striking difference with previous studies can be found in the relative position of the sharp peak arising from lanthanum. While in our calculations, and in those of Mishra et al [56], the 4f peak lies about 1-1.5 eV above the bottom of the conduction band (associated to the broad La 5d peak of the DOS), in the LSDA + U calculations of Singh et al [54] this difference is around 4 eV.…”

“…Except for the cases of La 2 TeO 6 and Y 2 TeO 6 , the electronic structure of the compounds included in this work has been studied previously using different computational approaches [45][46][47][48][49][52][53][54][55][56][57][58][59][60]. Since one of our principal aims is to obtain a general picture of the nature of the valence and conduction bands for all these compounds and its influence on the resulting optical properties, we will center our discussion on the density of states in the energy region around the band gap.…”

Lanthanum phosphate calcium aluminate glasses: 27Al and 31P NMR spectroscopy

“…[1][2][3] For example, phosphate glass use in optical components is increasing, and for this the glasses are stabilized by the addition of alumina. 4,5 Aluminates figure prominently in several scientific and engineering applications, for example as support structures for optically active components in electronic systems.…”

“…4,5 Aluminates figure prominently in several scientific and engineering applications, for example as support structures for optically active components in electronic systems. 2 Doping of both phosphate and aluminate glasses with rare earth elements allows tuning of the fluorescence of those elements. 2,6 Among materials for high-temperature applications, the refractory compound lanthanum-monazite (LaPO 4 ) has been intensively investigated because of its potential usefulness in * Corresponding author.…”