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Uniform spheres are highly desired for the fabrication of advanced ceramics and as phosphor for lighting and display. Green emitting (Y 0.95− x Gd x Tb 0.05 ) 2 O 3 phosphor spheres were successfully synthesized in this work via homogeneous precipitation, with particular emphases on size enlargement of the particles and the effects of particle size, Gd 3+ incorporation and calcination on photoluminescence. Ammonium nitrate (NH 4 NO 3 ) was originally used to effectively enlarge the precursor particles from ∼150 ± 10 to 590 ± 43 nm, whose effects were found to tend to saturate at NH 4 NO 3 :rare-earth = 1:1 molar ratio. Size enlargement up to ∼630 ± 57 nm has also been achieved via a self-seeded growth approach. The optimal Gd 3+ content for luminescence was determined to be 2 at% ( x = 0.02) for the phosphors, and the spin-allowed 7 F 6 → 7 D J Tb 3+ excitation at ∼278 nm successively lowers at a higher Gd 3+ content or calcination temperature owing to bandgap narrowing of the host lattice. Intensity of the 543 nm green emission steadily improves with increasing temperature of calcination or particle size, and the lifetime of the 543 nm emission, affected by particle size and calcination, falls in the range of ∼1.75–2.81 ms. The phosphors have similar color coordinates of around (0.32, 0.56), irrespective of the Gd content, particle size, and calcination temperature. [ABSTRACT FROM AUTHOR]

The two important groups of Ln 2 O 2 SO 4 and Ln 2 O 2 S compounds are traditionally synthesized with the involvements of environmentally harmful sulfur-containing reagents. We developed in this work a unique green approach for their synthesis, using Ln 2 (OH) 4 SO 4 ·2H 2 O layered hydroxyl sulfate as the precursor (Ln-241 phase). Phase selective crystallization of La-241 under both atmospheric pressure and hydrothermal conditions was firstly optimized, followed by transformation into La 2 O 2 S and La 2 O 2 SO 4 by controlled calcination. Rietveld structure refinement was performed for La-241, La(OH)SO 4 , La 2 O 2 SO 4 , and La 2 O 2 S, and the crystal structure and cell parameters of La-241 were originally reported. The photoluminescence performances of several important activators (Pr 3+ , Sm 3+ , Eu 3+ , Tb 3+ , and Dy 3+ ) in the two hosts, in terms of excitation, emission, quantum yield, and color coordinates of emission, were thoroughly investigated, and multi-color luminescence including bright red, green, orange red, and yellow was obtained under ultraviolet excitation. Detailed investigations of Tb 3+ photoluminescence revealed that the lack of 5 D 3 emission in La 2 O 2 S and the gradual quenching of 5 D 3 blue emission at a higher Tb 3+ content (hence decreasing I 488 /I 545 ratio and changing color coordinates) in La 2 O 2 SO 4 were suggested to be due to thermal activation of the 5 D 3 electrons into the conduction band and cross relaxation between adjacent Tb 3+ , respectively. The synthesis approach developed in this work for La 2 O 2 SO 4 and La 2 O 2 S, with water vapor as the only exhaust gas, is environmentally benign and holds great potential in the facile synthesis of analogous compounds of other lanthanides. [ABSTRACT FROM AUTHOR]