White LEDs (light-emitting diodes) are devices that emits white light in combination of a semiconductor light-emitting device and a phosphor and a typical known example thereof is a combination of a blue LED and a YAG (Yttrium Aluminum Garnet) yellow phosphor. However, YAG phosphors, which contain a smaller amount of red light-emitting component, have problems that they are inferior in color rendering properties for use in illumination application, and lose their color reproducibility when used as a backlight for image display devices such as liquid-crystal display devices.
As a method for improving the color rendering properties of white LEDs, proposed was a method of compensating the red component by using a YAG phosphor and a red light-emitting nitride-based phosphor in combination (see Patent Document 1). It is also known that, among red light-emitting nitride-based phosphors, CaAlSiN3-based nitrides or oxynitride materials that contain an inorganic compound having a crystalline structure identical with CaAlSiN3 crystalline phase as the host crystal and additionally an optically active element, in particular Eu, as the emission center emit orange to red light particularly at high brightness (see Patent Document 2).
It is possible to produce the CaAlSiN3-based nitride phosphor by using a mixture of the nitrides of the elements constituting the phosphor (see Patent Document 3). In the production method for a phosphor described in Patent Document 3, a phosphor is produced by mixing nitrides of the elements constituting the phosphor and calcining the mixture obtained in a calcination furnace, using nitrogen gas as the atmospheric gas.