SYNTHESIS AND LUMINESCENT INVESTIGATION ON THE CALCIUM SILICATE CA3 SI 2 O7 , ACTIVATED WITH EU2+ IONS

The thermodynamic analysis of possible chemical processes occurring in the system CaO:SiO2=3:2 was carried out. Optimized conditions for the preparation Ca3(1-х)Eu3xSi2O7 firm solutions have been determined. It was shown that the effective luminescence of Eu2+ions in Ca3Si2O7 with a maximum at 625 nm creates pre-conditions for the use of this material as a phosphor for white light-emitting diodes

Position of the optical absorption edge of alkaline earth borates

Based on the results of luminescent measurements on MB$_2$O$_4$ (M = Ca, Sr), Ca$_2$B$_5$O$_9$Cl, SrB$_6$O$_{10}$, SrAl_2$B_2O$_7$and the literature data, the influence of the crystal structure of alkaline earth borates on the position of their optical absorption edge is discussed. It is found that the optical absorption edge tends to shift to higher energy from β-BaB$_2$O$_4$(6.4 eV) to M$_3$(BO$_3$)$_2$, MB$_2$O$_4$(6.9–7.2 eV) to SrB$_6$O$_{10}$(7.7 eV), SrB$_4$O$_7$(>7.8 eV). It is shown that this tendency can be interpreted as a result of (a) the removal of M$^{2+}$ states from the top of the valence band; (b) a more efficient stabilization of the O 2p states by B–O covalent bonding with increasing condensation degree of the borate anion

Luminescence properties and electronic structure of Ce3+\mathrm{Ce^{3+}}-doped gadolinium aluminum garnet

Yttrium-gadolinium aluminum garnets (YGdAG) doped with Ce3+ ions have been prepared by co-precipitation method. The luminescent properties of Ce3+ ions in Gd3(1−x)Ce3xAl5O12 (х = 0.01) have been studied upon excitation in the 2–20 eV region. The substitution of Gd3+ for Y3+ in the garnet structure results in broadening the emission band and shifting its maximum towards the longer wavelengths. It was found that in addition to the 4f → 5d excitation bands of Ce3+ ions, the excitation spectra for the Ce3+ emission contain bands at 6.67, 7.75, and 9.76 eV. These bands are attributed to the Ce3+-bound exciton formation and O 2p → Al 3s, 3p transitions, respectively. Although gadolinium states dominate near the bottom of the conduction band of Gd3Al5O12, contributions from Altetr and Aloct atoms to the conduction-band density of states are evaluated as quite essential