The interest in nanoscale materials stems from the fact that new properties are acquired at this length scale and, equally important, that these properties * To whom correspondence should be addressed. Phone, 404-8940292; fax, 404-894-0294; e-mail, mostafa.el-sayed@ chemistry.gatech.edu. † Case Western Reserve UniversitysMillis 2258. ‡ Phone, 216-368-5918; fax, 216-368-3006; e-mail, burda@case.edu. § Georgia Institute of Technology. 1025 Chem. Rev. 2005, 105, 1025−1102

Chemistry and properties of nanocrystals of different shapes.

Mechanical alloying (MA) is a solid-state powder processng technique involving repeated welding, fracturing, and rewelding of powder particles in a high-energy ball mill. Originally developed to produce oxide-dispersion strengthened (ODS) nickel- and iron-base superalloys for applications in the aerospace industry, MA has now been shown to be capable of synthesizing a variety of equilibrium and non-equilibrium alloy phases starting from blended elemental or prealloyed powders. The non-equilibrium phases synthesized include supersaturated solid solutions, metastable crystalline and quasicrystalline phases, nanostructures, and amorphous alloys. Recent advances in these areas and also on disordering of ordered intermetallics and mechanochemical synthesis of materials have been critically reviewed after discussing the process and process variables involved in MA. The often vexing problem of powder contamination has been analyzed and methods have been suggested to avoid/minimize it. The present understanding of the modeling of the MA process has also been discussed. The present and potential applications of MA are described. Wherever possible, comparisons have been made on the product phases obtained by MA with those of rapid solidification processing, another non-equilibrium processing technique.

Mechanical Alloying And Milling

The development of novel materials is a fundamental focal point of chemical research; and this interest is mandated by advancements in all areas of industry and technology. A good example of the synergism between scientific discovery and technological development is the electronics industry, where discoveries of new semiconducting materials resulted in the evolution from vacuum tubes to diodes and transistors, and eventually to miniature chips. The progression of this technology led to the development * To whom correspondence should be addressed. B.L.C.: (504) 2801385 (phone); (504) 280-3185 (fax); bcushing@uno.edu (e-mail). C.J.O.: (504)280-6846(phone);(504)280-3185(fax);coconnor@uno.edu (e-mail). 3893 Chem. Rev. 2004, 104, 3893−3946

http://depa.fquim.unam.mx/amyd//archivero/FidelmarLechugaSanabria_4940.pdf

Recent advances in the liquid-phase syntheses of inorganic nanoparticles.

Phosphor-converted white light-emitting diodes (pc-WLEDs) are emerging as an indispensable solid-state light source for the next generation lighting industry and display systems due to their unique properties including but not limited to energy savings, environment-friendliness, small volume, and long persistence. Until now, major challenges in pc-WLEDs have been to achieve high luminous efficacy, high chromatic stability, brilliant color-rending properties, and price competitiveness against fluorescent lamps, which rely critically on the phosphor properties. A comprehensive understanding of the nature and limitations of phosphors and the factors dominating the general trends in pc-WLEDs is of fundamental importance for advancing technological applications. This report aims to provide the most recent advances in the synthesis and application of phosphors for pc-WLEDs with emphasis specifically on: (a) principles to tune the excitation and emission spectra of phosphors: prediction according to crystal field theory, and structural chemistry characteristics (e.g. covalence of chemical bonds, electronegativity, and polarization effects of element); (b) pc-WLEDs with phosphors excited by blue-LED chips: phosphor characteristics, structure, and activated ions (i.e. Ce 3+ and Eu 2+ ), including YAG:Ce, other garnets, non-garnets, sulfides, and (oxy)nitrides; (c) pc-WLEDs with phosphors excited by near ultraviolet LED chips: single-phased white-emitting phosphors (e.g. Eu 2+ –Mn 2+ activated phosphors), red-green-blue phosphors, energy transfer, and mechanisms involved; and (d) new clues for designing novel high-performance phosphors for pc-WLEDs based on available LED chips. Emphasis shall also be placed on the relationships among crystal structure, luminescence properties, and device performances. In addition, applications, challenges and future advances of pc-WLEDs will be discussed.

Phosphors in phosphor-converted white light-emitting diodes: Recent advances in materials, techniques and properties

Leu-M

http://nfudee.nfu.edu.tw/ezfiles/43/1043/img/341/A19%3DSynthesisandluminescentpropertiesofLn3%2B(Eu3%2B,Sm3%2B,Dy3%2B)-doped.pdf

Synthesis and luminescent properties of Ln3+ (Eu3+, Sm3+, Dy3+)-doped lanthanum aluminum germanate LaAlGe2O7 phosphors

Powders of ilmenite structure NiTiO 3 and CoTiO 3 were prepared by a simple method based on the modified Pechini process. The raw compounds and citric acid (CA) were mixed in ethanol (EA) with the molar ratio Ni(Co)/Ti/CA/EA = 1/1/1/7.5. The DTA curve shows exothermic peaks only around 300–350 °C and 600 °C, which correspond to the decomposition of the organic compound and direct crystallization of the ilmenite phase. X-ray diffraction patterns indicated that the ilmenite phase was successfully synthesized as the Ni(Co)-Ti precursor calcined above 600–900 °C for 3 h, and the activation energies of NiTiO 3 and CoTiO 3 were calculated to be about 8.84 and 13.23 kJ/mol. TEM bright field images showed that the grain sizes of powders of NiTiO 3 and CoTiO 3 at 600–900 °C were estimated to be about 10–250 and 20–200 nm depending on the nature of the aggregate. The samples of NiTiO 3 calcined at 600–800 °C have the larger specific surface area of 31.51, 18.78, and 6.01 m 2 /g, respectively. The UV-Vis diffuse reflectance spectra show the optical band gaps of NiTiO 3 and CoTiO 3 as 3.02 and 2.43 eV.

Synthesis and characterization of ilmenite NiTiO3 and CoTiO3 prepared by a modified Pechini method

Synthesis and characterization of zinc titanate nano-crystal powders by sol–gel technique

The novel phosphors of LaAlGe 2 O 7 doped with Gd 3+ and Tb 3+ were synthesized, and their luminescence properties were investigated. In Tb 3+ -activated LaAlGe 2 O 7 , the unusual excitation spectra showed only intense f-f transition of Tb 3+ ions around the near-UV region, whereas the 4f-5d transition could be neglected. In the Gd 3+ -Tb 3+ -activated system, the decay time of Tb 3+ emission under Gd 3+ excitation at the 6I J energy level was longer than that measured under direct Tb 3+ excitation at the 5 L 10 energy level, which reinforces the existence of effective Gd 3+ -to-Tb 3+ energy transfer. In the 5 D 4 decay measurements, time-resolved spectra exhibited a "grow-in" behavior as the Tb 3+ concentration was diluted ( 0.05 mol) Tb 3+ concentrations. Two linear relationships were found between the energy transfer probability (P Gd→1b ) and the Tb 3+ concentration, which is clear evidence that there were two kinds of efficient Gd 3+ -to-Tb 3+ energy transfer processes in terms of Tb 3+ concentration.

Luminescence and Energy Transfer Properties of Gd3+ and Tb3+ in LaAlGe2O7

Phosphors of LaAlGe2O7 doped with Tm3+ and Er3+ of high color purity, exhibiting a narrow band emission in the blue and green regions, were obtained. (La1−xLnx)AlGe2O7 (Ln=Tm,Er) powders are bright emitters, with chromaticity color coordinates that are comparable to or better than those of standard phosphors for display or lighting devices. The blue emission of the Tm3+-doped phosphor had CIE chromaticity coordinates (0.151, 0.033) with a dominant wavelength of 455nm and a color purity of 94%. The Er3+-doped phosphor had color coordinates (0.249, 0.718), a dominant wavelength of 542nm, and 92% purity.

/pdf/high-color-purity-phosphors-of-laalge2o7-doped-with-tm3-and-1a3ukekgbc.pdf

Yen-Hwei Chang

Papers

Synthesis and luminescent properties of Ln3+ (Eu3+, Sm3+, Dy3+)-doped lanthanum aluminum germanate LaAlGe2O7 phosphors

Synthesis and characterization of ilmenite NiTiO3 and CoTiO3 prepared by a modified Pechini method

Synthesis and characterization of zinc titanate nano-crystal powders by sol–gel technique

Luminescence and Energy Transfer Properties of Gd3+ and Tb3+ in LaAlGe2O7

High color purity phosphors of LaAlGe2O7 doped with Tm3+ and Er3+