Holly Ann Comanzo

Nature of luminescent centers in cerium-activated materials with the CaFe2O4 structure

Abstract The cerium luminescence in SrY 2 O 4 shows two bands emitting in the blue and green regions of the optical spectrum. Based on standard emission and excitation spectroscopy combined with time-resolved emission studies, we can attribute the blue emission to a Ce 3+ 5d–4f transition and tentatively assign the green emission to a “Ce 4+ –O 2− ”charge transfer transition.

Optical Spectroscopy and Crystal Field Studies of the Mn4+ Ion (3d3) in the Double Perovskite NaLaMgTeO6

The spectroscopic properties of the Mn4+ ion (3d3) in the double perovskite NaLaMgTeO6 are reported in this work. Evidence is presented for the occupation by the Mn4+ ion of both the six coordinated Mg2+ and Te6+ sites in the host structure. The Mn4+ energy levels are calculated using the exchange charge model of crystal field theory for both occupied sites. The results of our calculations yield the crystal field splitting and Racah parameters of Dq = 2008 cm−1, B = 790 cm−1, C =2881 cm−1, with C/B=3:65 (Mg2+ site) and Dq=2008 cm−1, B=790 cm−1,C =2949 cm−1, with C/B = 3:73 (Te6+ site). A cross-cutting comparative study of the variations in the crystal field splitting and the Racah parameters of the six-coordinated Mn4+ ion in a series of materials with the perovskite structure are presented. Graphical Abstract Optical Spectroscopy and Crystal Field Studies of the Mn4+ Ion (3d3) in the Double Perovskite NaLaMgTeO6

Ce3+-based phosphors for blue LED excitation

The luminescence of Ce3+ in host lattices based on Y3Al5O12 garnets that can be used in blue LED based solid state lighting sources is discussed. Specifically, the effect of Ga3+ and Tb3+ substitution for Al3+ and Y3+, respectively, on the emission color and thermal quenching of these phosphors is described with the initial implications for white light devices.

Microwave Sintering of ZnO Varistor Ceramics

ZnO varistors are electronic ceramics whose electrical behavior is dominated by grain boundary effects. A careful evaluation of the effect of microwave sintering compared to conventional sintering revealed no significant differences between varistor devices processed by these two methods. A slight apparent enhancement of grain growth was observed for microwave processing, but further evaluation of this effect leads us to believe that it arises from a small systematic shift in temperature derived from the different experimental configurations.