Local microstructural analysis for Y2O3/Eu3＋/Mg2＋ nanorods by Raman and photoluminescence spectra under high pressure

In this paper, we investigate the Raman and photoluminescence spectra of Y_2O_3/Eu^（3＋） and Y_2O_3/Eu^（3＋）/Mg^（2＋） nanorods under high pressures using 514-nm and 532-nm laser light excitation. We observe transitions from the initial cubic phase to amorphous at pressures higher than 24 GPa for both Y_2O_3/Eu^（3＋） and Y_2O_3/Eu^（3＋）/Mg^（2＋） nanorods. In addition, Y_2O_3/Eu^（3＋） and Y_2O_3/Eu^（3＋）/Mg^（2＋） nanorods exhibit different distorted states after the pressure has been raised to 8 GPa. The analyses of intensity ratios, I_（0-2）/I_（0-1） from ~5D_（0–）~7F2_to^5D_（0–）~7F_1and I_（0-2）A/B of ~5D_（0–）7F_2 transitions indicate that Y_2O_3/Eu^（3＋）/Mg^（2＋） nanorods exhibit stronger local micro-surrounding characteristics for Eu^（3＋） ions in a pressuremodulated crystal field. The doped Mg2＋ion results in reducing the crystal ionicity in the distorted lattice state under high pressures. The use of doped ions as an ion modifier can be applied to the study of small local microstructural changes through Eu^（3＋） luminescence.

Synthesis and Photoluminescence Properties of Uniform Y_2O_3:Eu^(3+) Hollow Spheres with Tunable Shell Thickness

Y2O3：Eu3＋ hollow spheres were successfully prepared with melamine formaldehyde（MF） spheres as template. The MF spheres played a significant role in directing the formation of the hollow shells which are composed of numerous primary nanoparticles. Furthermore, the shell thickness of these hollow spheres could be readily tailored by adjusting the dosage of MF template. Based on the photoluminescence（PL） investigation, the red emission intensities（613 nm） of these Y2O3：Eu3＋ hollow spheres are greatly influenced by their shell thickness and it was found that hollow spheres with thin shell thickness and intact hollow structures permit a better PL performance.

Crystalline phase of Y_2O_3 :Eu particles generated in a substrate-free flame process

In this study, factors affecting the crystal structure of flame-synthesized Y2O3 ：Eu particles were investigated, especially the particle size effect and its interaction with Eu doping concentration, Polydisperse Y2O3：Eu （size range 200 nm to 3μm） powder samples with Eu doping concentrations from 2,5 mol% to 25 mol% were generated in either H2/air or H2/O2 substrate-free flames. The crystal structure of the powder samples was determined by powder X-ray diffraction （XRD）, which was complemented by pho- toluminescence （PL） measurements. Single particle crystal structure was determined by single particle selected area electron diffraction （SAED）, and for the first time, by electron backscatter diffraction （EBSD）. H2/air flames resulted in cubic phase Y2O3：Eu particles with hollow morphology and irregular shapes, Particles from H2/O2 flames had dense and spherical morphology; samples with lower Eu doping concen- trations had mixed cubic/monoclinic phases; samples with the highest Eu doping concentrations were phase-pure monoclinic. For samples generated from H2/02 flames, a particle size effect and its interaction with Eu doping concentration were found： particles smaller than a critical diameter had the monoclinic phase, and this critical diameter increased with increasing Eu doping concentration, These findings suggest that the formation of monoclinic Y2O3：Eu is inevitable when extremely hot substrate-free flames are used, because typical flame-synthesized Y203 ：Eu particle sizes are well below the critical diameter, However, it may be possible to generate particles with dense, spherical morphology and the desired cubic structure by using a moderately high flame temperature that enables fast sintering without melting the particles.