LED lamps using phosphor downconversion can be designed to replace incandescent or halogen sources with a "warm-white" correlated color temperature (CCT) of 2700-3200 K and a color rendering index (CRI) greater than 90. However, these lamps have efficacies of ∼70% of standard "cool-white" LED packages (CCT = 4500-6000 K; CRI = 75-80). In this report, we describe structural and luminescence properties of fluoride and oxyfluoride phosphors, specifically a (Sr,Ca) 3 (Al,Si)O 4 (F,O):Ce 3þ yellow-green phosphor and a K 2 TiF 6 :Mn 4þ red phosphor, that can reduce this gap and therefore meet the spectral and efficiency requirements for high-efficacy LED lighting. LED lamps with a warm-white color temperature (3088 K), high CRI (90), and an efficacy of ∼82 lm/W are demonstrated using these phosphors. This efficacy is ∼85% of comparable cool-white lamps using typical Y 3 Al 5 O 12 :Ce 3þ -based phosphors, significantly reducing the efficacy gap between warm-white and cool-white LED lamps that use phosphor downconversion.

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Lithium intercalation in phase-pure nanocrystalline brookite TiO 2 is demonstrated for the first time. Galvanostatic studies show that 0.9 Li per formula unit can be intercalated into this phase in initial discharge. Ex situ X-ray diffraction studies on the electrodes at different levels of lithium intercalation show that the structure is stable toward lithium intercalation and deintercation. In the initial charge, an irreversible capacity loss is observed. However, on further cycling, the phase shows excellent cycling behavior. A reversible capacity of 170 mAhg −1 is observed even after 40 cycles.TiO 2 exists in eight crystal modifications and among them anatase, TiO 2 B, ramsdellite and hollandite are well studied for chemical or electrochemical lithium intercalation. 1-6 It has been shown that at elevated temperature ͑120°C͒, lithium can be intercalated into rutile TiO 2 . 7 With a simultaneous report by Hu et al., 8 recently we have demonstrated the lithium insertion into nanophase rutile TiO 2 , synthesized at room temperature ͑RT͒. 9 The rutile phase, however, undergoes an irreversible phase transformation from tetragonal to hexagonal Li x TiO 2 structure upon Li insertion with a capacity of 140 mAhg −1 at 1.5 V vs Li/Li + . 9 These studies emphasize the role of the particle size in determining the reactivity of the rutile phase towards lithium. We decided then to revisit another allotropic form of titanium dioxide, namely, the brookite phase. There are no conclusive studies on Li insertion in this phase even though some suggestions were made to this effect. 5 Herein, we report, for the first time, the intercalation of Li into the nanophase brookite TiO 2 . About 0.9 Li per formula unit can be intercalated. The structural integrity is maintained after Li intercalation. ExperimentalBrookite TiO 2 was prepared by thermolysis of TiCl 4 at 100°C in concentrated HCl solution as described by Pottier et al. 10 Typical synthesis was as follows: In a 500 mL reagent bottle 250 mL of 3 M HCl was taken and 0.15 M TiCl 4 was added slowly. The bottle was closed and kept at 100°C in an oven for 48 h. After thermolysis, the obtained white precipitate was separated by centrifugation. At this stage, the sample consists of both brookite and rutile phases. The rutile phase was separated by peptization in a 3 M nitric acid followed by centrifugation. Finally, the obtained residue was dispersed in water and centrifuged at 10000 rpm for 10 min. The centrifugate was collected and freeze dried to obtain pure brookite TiO 2 . The as obtained sample was dried at 100°C for 4 h and used for electrochemical studies and other characterization. X-ray diffraction ͑XRD͒ patterns were collected in the 2 range 10-100°using a Philips X'pert diffractometer with Bragg-Brentano geometry ͑Cu K␣ rad͒. Electron diffraction study was carried out on a JEOL 200CX transmission electron microscope ͑TEM͒ equipped with a KEVEX analyzer ͑energy dispersive spectroscopy, EDS͒. For electrochemical studies, electrodes were fabricated by mixing active material, ...

In this article, we describe various oxide, oxyhalide, and halide phosphors that can be used in combination with blue light emitting diodes (LEDs) for lighting and display systems. Within specific host-activator combinations, we briefly discuss composition-property relationships and the potential impact upon LED system performance. In addition, some of the practical drawbacks and open issues for many of these materials are discussed, giving potential routes for future work.