Publication Date:
2015-02-12
Description:
Chemical precipitation at the freezing temperature of ~4°C has directly yielded layered rare-earth hydroxide [LRH, Ln 2 (OH) 5 NO 3 · n H 2 O, Ln = Y 0.95 Eu 0.05 ] nanosheets (up to 7 nm thick) for the Y/Eu binary system, with the interlayer NO 3 − exchangeable with SO 4 2− . Calcining the sulfate derivative at 1100°C for 4 h produces well-dispersed and readily sinterable Ln 2 O 3 red phosphor powders (~14.8 m 2 /g) that can be densified into highly transparent ceramics via optimized vacuum sintering at the relatively low temperature of 1700°C for 4 h (average grain size ~14 μm; in-line transmittance ~80% at the 613 nm Eu 3+ emission or ~99% of the theoretical transmittance of Y 2 O 3 single crystal). Our systematic studies also found that (1) the extent of SO 4 2− exchange and the interlayer distance of LRH are both affected by the SO 4 2− /Ln 3+ molar ratio ( R ), and an almost complete exchange is achievable at R = 0.25 as expected from the chemical formula (one SO 4 2− replaces two NO 3 − for charge balance). The optimal R value for sintering, however, was found to be 0.03; (2) The Ln 3+ concentration for LRH synthesis substantially affects properties of the resultant oxides, and hard agglomeration has been significantly reduced at the optimized Ln 3+ concentration of 0.05–0.075 mol/L; (3) Sulfate exchange significantly alters the thermal decomposition pathway of LRH, and was found essential to produce well-dispersed and highly sinterable oxide powders; (4) Both the oxide powders and transparent ceramics exhibit the typical red emission of Eu 3+ at ~613 nm (the 5 D 0 7 F 2 transition) under charge-transfer (CT) excitation. Red-shifted CT band center, stronger excitation/emission, and shorter fluorescence lifetime were, however, observed for the transparent ceramics.
Print ISSN:
0002-7820
Electronic ISSN:
1551-2916
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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