The Inductive Effect in Nitridosilicates and Oxysilicates and Its Effects on 5d Energy Levels of Ce3+

Inorg. Chem. 2018, 57, 4, 2320–2331. https://doi.org/10.1021/acs.inorgchem.7b03253

The inductive effect exists widely in inorganic compounds and accounts well for many physicochemical properties. However, until now this effect has not been characterized quantitatively. In this work, we collected and analyzed the structural data of more than 100 nitridosilicates and oxysilicates, whose structures typically consist of [SiN4] or [SiO4] tetrahedra. We introduce a new parameter, the inductive effect factor μΔχ, related to the difference of electronegativity between constituent metal elements and silicon. Then, a linear relationship is established between average length of Si–N/Si–O bonds and the inductive factor with the help of statistical method, that is, l̅ = 1.7313 + 0.0166 μΔχ (Å) with adjusted (adj) R2 = 0.800 for Si–N and l̅ = 1.6221 + 0.0035 μΔχ(Å) with adj R2 = 0.240 for Si–O. Furthermore, our research shows that the distinct positive correlation does exist between the inductive factor and the centroid shift of 5d levels of Ce3+. This work will help us understanding the inductive effect deeply and quantitatively.

After-glow, luminescent thermal quenching, and energy band structure of Ce-doped yttrium aluminum-gallium garnets

Journal of Luminescence, 2017,9, 192

Yttrium aluminum-gallium garnets with cerium doped is most widely used as green-yellow phosphor in solid state lighting. Extensive research has been performed on this material concerning the luminescent thermal quenching resistance and persistent luminescence. In this paper we find that a negative correlation exists between temperature-dependent luminescence and persistent luminescence with gallium content varying. The correlation originates from the electronic structures which influence both the thermal quenching of luminescence and persistent luminescence. A detailed crystal-field calculation has been performed to understand the peak shifts. In addition, theoretical calculations reveal that oxygen vacancies provide trap levels which implement the persistent luminescence. This material could be used as potential blue-light excited persistent luminescent material, with the after-glow time up to about 1. h with only cerium as the dopant, which is expected to be prolonged by co-doping other elements. This work may be helpful in guiding the discovery of other after-glow materials.

Crystal Structure and Photoluminescence Evolution of La5(Si2+xB1–x)(O13–xNx):Ce3+ Solid Solution Phosphors

J. Phys. Chem. C., 2015, 119, 17, 9488. https://pubs.acs.org/doi/10.1021/acs.jpcc.5b01211

A series of iso-structural La5(Si2+xB1–x)(O13–xNx):Ce3+ phosphors with apatite structure have been prepared. A combination of powder X-ray diffraction and neutron scattering technique was employed to explore the crystal structural evolution and the rigid nature from oxy- to oxynitride-based apatites, and some local structures were also characterized by HRTEM and 29Si NMR data, respectively. The new La5(Si2+xB1–x)(O13–xNx):Ce3+ solid solution phosphors gave continuously controlled emission from 421 nm [La5Si2BO13:Ce3+, end-member (x = 0)] to 463 nm (La5Si3O12N:Ce3+, end-member (x = 1)). Substitution of B3+ and O2– by Si4+ and N3– in La5(Si2+xB1–x)(O13–xNx):Ce3+ phosphors produced more covalency into the crystal field environment around the Ce3+ ions inducing the red-shifted emission, further improving the thermal stability of the oxynitride-based apatite phosphors. The proposed approach from oxy- to oxynitride based iso-structural phases could significantly contribute to future research in designing complex solid solution phosphors.

Crystal structure and photoluminescence of (Y1−xCex)2Si3O3N4

J. Lumin., 2011, 131, 2, 336. https://doi.org/10.1016/j.jlumin.2010.10.032

Oxonitridosilicate phosphors with compositions of (Y1−xCex)2Si3O3N4 (x=0−0.2) have been synthesized by solid state reaction method. The structures and photoluminescence properties have been investigated. Ce3+ ions have substituted for Y3+ ions in the lattice. The emission and excitation spectra of these phosphors show the characteristic photoluminescence spectra of Ce3+ ions. Based on the analyses of the diffuse reflection spectra and the PL spectra, a systematic energy diagram of Ce3+ ion in the forbidden band of sample with x=0.02 is given. The best doping Ce content in these phosphors is ∼2 mol%. The quenching temperature is ∼405 K for the 2 mol% Ce content sample. The luminescence decay properties were investigated. The primary studies indicate that these phosphors are potential candidates for application in three-phosphor-converted white LEDs.

Crystal structure and photoluminescence of (La1-xCex)5Si3O12N

J. Alloys Compd., 2011, 509, 5, 2099. https://doi.org/10.1016/j.jallcom.2010.10.148

Oxonitridosilicate phosphors with compositions of (La1−xCex)5Si3O12N (x = 0–0.1) have been synthesized. The XRD analyses show that all the compounds are single polycrystalline La5Si3O12N phase. La atoms occupy two crystallographic sites in the structure. Two groups of photoluminescence spectra have been observed and can be ascribed to the excitation and emission of the two types of Ce3+ photoluminescence centers (Ce(1)3+ and Ce(2)3+) in the crystallographic sites of La(1) and La(2). The energy transfer between the two types of photoluminescence centers has been discussed. Schematic energy levels of Ce3+ ions at the two crystallographic sites are given. Luminescence concentration quenching occurs when Ce content is more than 3 mol%. The quenching temperature is evaluated to be about 406 K for the 3 mol% Ce content sample. This study shows these phosphors potential candidates for application in three-phosphor-converted white LEDs.

Synthesis, structure and luminescence of LaSi3N5:Ce3+ phosphor

J. Lumin., 2009, 129, 3,165. https://doi.org/10.1016/j.jlumin.2008.08.005

In this work, new LaSi3N5:Ce3+ phosphors have been synthesized by solid-state reaction. Rietveld refinement of the crystal structure of La1−xCexSi3N5 reveals that Ce atoms substituted for La atoms occupy 4a crystallographic positions. Broad emission and excitation bands observed were attributed to the transitions between the doublet ground state of the 4f1 configuration and the crystal field components of the 5d1 excited state. At 77 K, the centroid and crystal field splitting εcfs of the 5d levels of Ce3+ in LaSi3N5:Ce3+ compounds were valuated at 33.4×103 and 11.3×103 cm−1, respectively. The zero-phonon line and the Stokes shift were measured to be 26.0×103 and 5.0×103 cm−1, respectively.