The optical spectroscopic properties of Cr3+ in LiNbO3 have been investigated using optical absorption, fluorescence, fluorescence line narrowing (FLN), selective excitation and radiative lifetime measurements. The present results are compared with data obtained using other techniques including electron spin resonance (ESR) and electron nuclear double resonance (ENDOR), and shown to be consistent with there being five Cr3+ centres. The predominant centre is due to substitution at the Li+ site, which provides the weak crystal field in which Cr3+ ions emit into a broad 4T2 to 4A2 band. Using FLN, two centres experiencing a stronger crystal field are shown to be due to substitution at this same site, probably perturbed by the location of Nb5+ antisites and Nb5+ vacancies in the next-nearest-neighbour cation shell. The addition of Mg2+ ions to LiNbO3 appears not to create new Cr3+ complexes: rather it modifies the nature of the disorder, thereby changing the relative concentrations of the different centres. To this extent it becomes possible to identify two other lightly occupied Cr3+ centres where substitution is at the Nb5+ site. This total of five Cr3+ centres in LiNbO3 gives a consistent interpretation of all the available spectroscopic evidence, including ESR and ENDOR, while pointing to the difficulties of theoretical work in sites where the differences in the energy levels of Cr3+ ions are too small to be distinguished by the available models.

https://iopscience.iop.org/article/10.1088/0953-8984/7/49/026/pdf

Characterization of Cr3+ centres in LiNbO3 using fluorescence line narrowing

This paper presents a cluster approach to the calculation of the g factor in RX:V 2+ (R=Na,K,Rb; X=Cl,Br), in which not only the contribution due to the spin-orbit coupling of the central transition-metal ion but also that of the ligands are included. The calculated results agree well with the available experimental data. The results show that the contribution to the g shift due to the spin-orbit coupling of the ligands is small in RCl:V 2+ but is about 80% of that of the central transition-metal ion in RBr:V 2+

Theoretical investigation of the g factor in RX:V2+ (R=Na,K,Rb;X=Cl,Br).

sichuan normal univ,inst solid state phys,chengdu 610066,peoples r china. acad sinica,int ctr mat phys,shenyang,peoples r china. sichuan normal univ,dept phys,chengdu,peoples r china.;chen, jj (reprint author), sichuan teachers coll,dept phys,nanchung 637002,peoples r china

Investigation on the gyromagnetic factor of ni(ii), v(ii), and cr(iii) in csmgx3 (x=cl,br,i)

Rutile-type compounds. IV. SiO2, GeO2 and a comparison with other rutile-type structures Locality: Meteor Crater, Arizona, USA

A complete diagonalization (of energy matrix) method based on the cluster approach (where the covalence effect due to the admixture between the orbitals of the central d(n) ion and that of ligands is considered) was applied to calculate the spin-Hamiltonian parameters (g factors, g(parallel to) and g(perpendicular to), and hyperfine structure constants, A(parallel to) and A(perpendicular to)) for two Cu2+ centers in ZnGa2O4 spinel at the temperature T approximate to 110 K. In both Cu2+ centers, Cu2+ ions occupy the trigonally-distorted octahedral sites 16d and the octahedrons undergo the static Jahn-Teller distortions from trigonal to tetragonally-elongated and tetragonally-compressed, respectively. The calculated spin-Hamiltonian parameters of the elongated Cu2+ center show good agreement with the experimental values and those of the compressed Cu2+ center are close to the observed values. The better agreement of spin-Hamiltonian parameter between calculation and experiment for the compressed Cu2+ center can be acquired by considering a small admixture of vertical bar d(x2-y2)> state to the vertical bar d(z2)> ground state due to the vibrational motion of ligands. The defect structures of both Cu2+ centers (characterized by the ligand displacements a(1) and a(2), respectively) in ZnGa2O4 spinel were also determined from the calculation.

Studies on the spin-Hamiltonian parameters of two Cu2+ centers and their defect structures due to Jahn-Teller effect for Cu2+-doped ZnGa2O4 spinel

A perturbation expression of the gyromagnetic factor of d3 ions is derived considering the spinorbit coupling of the ligand ions and taking into account all the excited states besides 4T2 state. The molecular orbital coefficients are determined by means of a semiempirical method in estimating the g-shift. The results show that the contribution of the spin–orbit coupling of the ligand ions to the g-shift must be considered for ligand ions possessing large spin–orbit coupling constants. The g-shifts of CsVX3 are calculated and the results agree well with experimental data.



Ein Storungsausdruck des gyromagnetischen Faktors von d3-Ionen wird abgeleitet, wobei die Spin–Bahn-Kopplung der Ligandenionen berucksichtigt wird, sowie alle angeregten Zustande, neben dem 4T2-Zustand. Die Molekularorbital-Koeffizienten werden mittels einer halbempirischen Methode fur die Berechnung der g-Verschiebung bestimmt. Die Ergebnisse zeigen, das der Beitrag der Spin–Bahn-Kopplung der Ligandenionen zur g-Verschiebung fur Ligandenionen mit grosen Spin–Bahn-Kopplungskonstanten berucksichtigt werden mus. Die g-Verschiebungen von CsVX3 werden berechnet und die Ergebnisse stimmen gut mit experimentellen Werten uberein.

Gyromagnetic Factor and Spin–Orbit Coupling of Ligands in CsVX3 (X = Cl, Br, I)

High-order perturbation formulae of the spin-Hamiltonian parameters D and E and the g-factor for the ground state 3A2(F) of d8 ions are obtained in the strong-field coupling scheme. In the derivation, not only spin triplet states but also spin singlet states are considered. According to Zhao's μkα-correlation ligand field model for the Ni2+−6X−(F−, Cl−, Br−, I−) complexes, the relationships between the spin-Hamiltonian parameters and the crystalline ones of the Ni2+−6X− cluster are established and applied to ZnF2:Ni2+ and NiF2. In the calculation, no adjustable parameter is introduced. The results agree well with the experimental findings, indicating that the given relationships are reasonable.



Storungsformeln hoherer Ordnung fur die Spin-Hamiltonparameter D, E und den g-Faktor werden fur den Grundzustand 3A2(F) von d8-Ionen im Fall des starken Kopplungsfeldes erhalten. In der Ableitung werden nicht nur Spintriplett sondern auch Spin-Singulettzustande betrachtet. Entsprechend dem μkα;-Korrelationsligandenfeldmodells von Zhao fur Ni2+-6X−(F−, Cl−, Br−, I−)- Komplexe werden die Beziehungen zwischen den Spin-Hamiltonparametern und den Kristallparametern des Ni2+-6X−-Clusters aufgestellt und auf ZnF2: Ni2+ und NiF2 angewendet. In die Berechnung werden keine anpasbaren Parameter eingefuhrt. Die Ergebnisse stimmen gut mit experimentellen Ergebnissen uberein und zeigen, das die angegebenen Beziehungen vernunftig sind.

High-Order Perturbation Formulae of the Spin-Hamiltonian Parameters for the Ground State3A2(F) of d8 Ions in Rhombic Symmetry

The dependence of the optical spectrum of the Mn 2+ -6F - cluster in crystals upon the true metal-ligand (M-L) bond length is studied by using a new refinement technique for the determination of the structure. Calculations show that the present theory gives a unified explanation for the d-d transition spectra, the paramagnetic properties, and thermal expansion of RbMnF 3 and KMgF 3 :Mn 2+

Min-Guang Zhao

Papers

Gyromagnetic Factor and Spin–Orbit Coupling of Ligands in CsVX3 (X = Cl, Br, I)

High-Order Perturbation Formulae of the Spin-Hamiltonian Parameters for the Ground State3A2(F) of d8 Ions in Rhombic Symmetry

Determination of the True Metal‐Ligand Bond Lengths from the Optical Spectrum for Transition‐Metal Ions in Crystals

Determination of the EPR ParameterD from the Optical Spectra for Cr3+ : LiNbO3

The Relationship between the Pressure and Zero-Field Splitting of ZnSiF6·6H2O:Ni2+ and the Determination of Its Equations of State