Stability of divalent/trivalent oxidation state of europium in some Sr-based inorganic compounds

Journal of Luminescence 132 (2012) 1768-1773

This work investigates the stability of Eu2+ and Eu3+ in some Sr-based inorganic compounds. Generally reducing condition is adopted in order to obtain Eu2+, however, the Eu doped SrAl2O4/SrLaAlO4 case indicates that for some compounds Eu3+ is stabilized even in reducing atmosphere. Bond valence method is applied to explain this phenomenon and it reveals that crystal structure also determines the valence state of europium cations along with reducing/oxidizing condition. An analysis of other Eu doped Sr-based materials is performed which shows the relationship between Eu2+/Eu3+ stability and the Global Instability Index (GII). This research provides a guideline for synthesizing specific novel Eu2+/Eu3+ phosphors.

Photoluminescence properties of Y5Si3O12N:Ce3+ blue-emitting phosphors for white LED

Journal of Alloys and Compounds 521 (2012) 77-82

Blue oxonitridosilicate phosphors with compositions of (Y1−xCex)5Si3O12N (x = 0–0.1) have been synthesized. The structures, photoluminescence properties and the relations between the structure and luminescence have been investigated and discussed. The atomic positions and the lattice parameters of Y5Si3O12N were acquired. Y atoms occupy two crystallographic sites (Y(1) and Y(2)) in the structure. Ce3+ ions were substituted for Y3+ ions and two types of photoluminescence centers (Ce(1)3+ and Ce(2)3+) have been formed. The excitation and emission processes of Ce(1)3+ and Ce(2)3+ photoluminescence centers were identified and studied. The concentration- and temperature-dependent properties of these Y5Si3O12N:Ce3+ phosphors were investigated. This study shows these blue Y5Si3O12N:Ce3+ phosphors the potential applications in the three-RGB phosphor-converted white LEDs.

An investigation of crystal chemistry and luminescence properties of Eu-doped pure-nitride α–sialon fabricated by the alloy-nitridation method

journal of luminescence 132 (2012) 2390-2397

A novel synthesis route of Eu2+-doped pure-nitride α-sialons has been reported. It is through an alloy-nitridation method at ∼2173 K in nitrogen atmosphere, with stable alloys (CaAl, SiEu), AlN, and α-Si3N4 powders as starting materials. A linear relationship between the lattice parameters and m values of (Ca0.995Eu0.005)m/2Si12−mAlmN16 compositions is obtained, indicating that our samples contain very little oxygen, i.e. herein so-called Eu-doped pure-nitride α-sialons. The (Ca0.995Eu0.005)m/2Si12−mAlmN16 compounds with 2.4≤m≤4.0 give the strongest emission. The emission shifts to longer wavelength with m values increasing as well as Eu contents increasing. (Ca0.995Eu0.005)m/2Si12−mAlmN16 compositions with smaller m values exhibit better thermal quenching properties.