The polarized optical spectra of the ions Ti3+, V3+, Cr3+, Mn3+, Co3+, and Ni3+ in corundum single crystals have been studied at temperatures from 4.2° to 1200°K. A theory of the band strength based on the point‐charge model and p‐d mixing has been developed and applied to the data with results in fair agreement with experiment. The effects of temperature show that the vibrational‐electronic contribution to band strength is quite small at low temperature but may be appreciable at high temperatures. The crystal‐field parameters have been calculated as convergent lattice sums. The observed trigonal‐field parameter has the opposite sign from that calculated by the point‐charge model if the impurity ion is assumed to occupy an Al3+ ion position in the lattice, but has the same sign as calculated for an ion 0.1 A displaced along the c3 axis toward the empty octahedral site. Details of the spectra have been interpreted as showing that the surroundings of an ion are distorted in some electronic states.

Optical spectra of transition-metal ions in corundum

Here we report a series of multifunctional Cr3+-doped magnesium gallogermanate particles Several minutes of ultraviolet (UV) light excitation can lead to strong near-infrared (NIR) long persistent luminescence (LPL) at 600–850 nm with a long lasting time of at least 25 h After the disappearance of LPL, NIR photostimulated persistent luminescence (PSPL) can be rejuvenated repeatedly several times by an external photostimulus (visible or NIR light) Meanwhile, the material shows photochromic (PC) properties, ie, the surface color can change reversibly between white/pale green and rosybrown with high fatigue resistance by alternating UV and visible light irradiation When the temperature is increased to 300 °C, the induced rosybrown surface color can also be bleached This new multifunctional material has potential applications in a wide range of fields, such as in vivo bio-imaging, optical information write-in and read-out media, erasable optical memory media and optical sensors The continuous trap distribution and modulation were characterized The optimum trap depth was determined to be 051–086 eV In addition, we gained insight into the mechanism of multifunctional properties and the interconnection between them

Multifunctional near-infrared emitting Cr3+-doped Mg4Ga8Ge2O20 particles with long persistent and photostimulated persistent luminescence, and photochromic properties

Ligand-field models and the photochemistry of coordination compounds

Complexes of CrIII and MnII of general formula [Cr(L)X2] X and [Mn(L)X2] respectively were prepared from N2O2, N2S2 and N4 donor macrocyclic ligands. The complexes have been characterized by elemental analysis, molar conductance measurements, spectral methods (i.r, mass, 1H-n.m.r, electronic spectra and e.p.r.) and magnetic measurements. The macrocyclic ligands have three different donating atom cavities, one with two unsaturated nitrogens and the other two have saturated nitrogen, oxygen and sulphur atoms. The effect of different donor atoms on the spectra and ligand field parameters is discussed. All the complexes show magnetic moments corresponding to a high-spin configuration. On the basis of spectral studies a six coordinated octahedral geometry may be assigned to these complexes.

Synthesis and spectral studies on mononuclear complexes of chromium(III) and manganese(II) with 12-membered tetradentate N 2 O 2 , N 2 S 2 and N 4 donor macrocyclic ligands

Near-infrared (NIR) phosphor-converted light-emitting diodes (pc-LEDs) have great potential in photonic, optoelectronic and biological applications, while the discovery of a broad-band NIR phosphor still remains a challenge. Here, we report a novel Cr3+-activated MgTa2O6 phosphor with an asymmetrical emission band ranging from 700 to 1150 nm and a large full width at half maximum (FWHM) of 140 nm upon 460 nm blue light excitation. The broad spectrum is assigned to the overlap of two bands centered at 910 and 834 nm, which originate from the spin-allowed transition of 4T2 → 4A2 for different Cr3+ ions located in the two six-coordinated crystallographic sites of Mg2+ and Ta5+, respectively. The distribution of blood vessels and bones in human palm and wrist is observed with the assistance of a commercial NIR camera and a fabricated pc-LED, which demonstrates that the MgTa2O6:Cr3+ phosphor is promising in biological applications.

Two-site Cr3+ occupation in the MgTa2O6:Cr3+ phosphor toward broad-band near-infrared emission for vessel visualization

Electronic spectra of quadrate chromium(III) complexes

In the presence of spin-orbit interaction, in addition to the well-known weak-field coupling scheme for cubic complexes in which the ligand field perturbation is applied last, we show that it is possible to devise a second weak-field coupling scheme in which the spin-orbit perturbation is applied last by constructing the corresponding energy matrices for d
2,8 electronic configurations. We also show that for the parameters applicable to actual experimental systems, the new weak-field coupling scheme yields purer eigenfunctions than the well-known weak-field coupling scheme.

Jayarama R. Perumareddi

Papers

Electronic spectra of quadrate chromium(III) complexes

A new weak-field coupling scheme for cubic complexes