The use of mercury in common mass-produced products is declining because of environmental concerns and increased governmental regulation. This trend keenly affects the lighting industry since mercury has been a primary material in the manufacture of lamps for decades, particularly fluorescent lamps.
In view of this, recent efforts have been made to reduce or eliminate mercury in fluorescent lamps. For example, PCT Patent Application No. WO 02/103748 describes a low-pressure gas discharge lamp based on an indium-containing gas filling. In particular, the lamp contains an indium halide, e.g., indium chloride, and an inert gas. The radiation emitted by the discharge has emission bands around 304, 325, 410 and 451 nm, as well as a continuous molecular spectrum in the visible blue range. A number of phosphors are listed for supplementing the radiation from the discharge in order to obtain white light. PCT Patent Application No. WO 2005/0456881, which is incorporated herein by reference, extends the list of available phosphors to use with the indium halide discharge to nitridosilicate and oxonitridosilicate phosphors.
In order to apply a phosphor coating to the inner surface of a glass tube to produce a fluorescent lamp, the phosphor powders are mixed into slurries containing a polymer and various other liquids. These liquids can be organic solvents and/or water, depending on which polymer is being used. After the coating is applied to the glass and dried, the coating is generally baked at >500° C. in an air atmosphere in order to decompose the polymer and leave behind only the phosphor layer. However, nitridosilicate and oxonitridosilicate phosphors tend to degrade significantly as a result of the baking process which makes them generally unsuited for use in a conventional fluorescent lamp manufacturing process.