Lauren E. Shea-Rohwer

Highly Versatile Rare Earth Tantalate Pyrochlore Nanophosphors

Rare earth tantalate materials are of considerable interest in energy and environmentally related applications including photocatalytic H(2) generation or contaminant decomposition, ion conductivity for batteries and fuel cells, and phosphors for light-emitting diodes (LEDs). These Eu-doped rare earth tantalate pyrochlore nanoparticles, K(1-2x)LnTa(2)O(7-x):Eu(3+) (Ln = Lu, Y, Gd; x = (1)/(3) for Gd, x = 0 for Lu and Y), have quantum yields up to 78% when excited with blue light (464 nm), which is remarkable for nanoparticle forms that can suffer efficiency loss by surface effects or poor crystallinity, and are furthermore quite suitable for LED applications. The Gd analogue with its framework distortions has particularly high quantum yields. The blue excitation peak matches the emission of the GaN LED. The combination of the high quantum yield under blue excitation, low thermal quenching, and chemical stability renders these new materials promising red phosphors for blue-excitation white LEDs for solid-state lighting. In addition, the pyrochlore lattice is very accommodating to dopants and vacancies and will incorporate virtually any metal and coordination environment ranging from four-coordinate to eight-coordinate. Thus, there are virtually unlimited possibilities for tailoring and optimizing photoluminescent properties, as demonstrated by these scoping studies.

Increasing the Luminescent Quantum Yield of CdS Nanoparticles Having Broadband Emission

Studies of the quantum yield (QY) of CdS quantum dots (QDs) with broadband luminescence are presented. These QDs are synthesized using the classic inverse micelle method employing the surfactant dioctyl sulfosuccinate sodium salt in heptane. Previous studies have shown that the QY of these materials is in the range of 10-13%. We have found that dehydration and UV photolysis roughly double the QY to typically ∼20%, while only slightly redshifting the emission. Dehydration is accomplished by cooling the samples to -30°C to remove the water from the inverse micelles. The addition of trialkylamines to dehydrated, photolyzed solutions results in a further improvement in QY to 37%. This effect is independent of amine chain length over the range studied.