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.
To model the flotation process, we have used the microscopic method developed by Scheludko et al.,
to study the stability of an aqueous thin film containing tetradecyltrimethylammonium bromide (C14TAB)
between an air bubble and a silica substrate. The experiments were performed at a range of C14TAB
concentrations and pH values. Spontaneous rupture of the thin aqueous film was interpreted in terms of
the earlier proposed heterocoagulation mechanism and resulted from the preferential adsorption of relatively
low surfactant concentrations at the vapor/solution interface causing a net positive charge while the solution/silica interface remained negatively charged. This attractive electrostatic interaction was sufficient to
overcome the van der Waals repulsion. At higher amine concentrations, the negative charge at the solution/silica interface was reversed. Finally, on approaching the critical micelle concentration (cmc), both interfaces
were sufficiently positively charged to cause the restabilization of the film by electrostatic repulsion. In
addition, in dilute solution, during the three-phase-contact (TPC) expansion or dewetting step following
film rupture, it was suggested that the movement of TPC across the silica substrate leads to transfer of
amine from the vapor/solution interface to the vapor/silica. This process resembles a Langmuir−Blodgett
deposition process and emphasizes the importance of the solution/vapor interface in the dewetting process.
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