Fluorescent lamp

A mercury vapour discharge fluorescent lamp (10) is provided having a phosphor layer (16) that has a yttria-based red emitting rare earth phosphor. The phosphor layer (16) is prepared from an aqueous phosphor slurry that is coated onto the inner surface of the glass envelope (12) of the lamp, then baked in a lehring oven to vaporize or decompose non-phosphor components of the slurry to leave behind the finished phosphor layer. The phosphor slurry contains a non-ionizing thickener, preferably polyethylene oxide, but does not contain any calcium carbonate or carbonate salts.