We have investigated the luminescence of a series of M5Eu(WO4)(4-x)(MoO4)(x) (M = Li, Na, K) phosphors and discovered that Na5Eu(WO4)(4-x)(MoO4)(x) (0 <= x <= 4.0) exhibit the most intense red emission among the three investigated. Powder X-ray diffraction investigations show that a complete solid solution can be formed in the indicated composition range. The effect of chemical compositions on the luminescence properties of Na5Eu(WO4)(4-x)(MoO4)(x) has been investigated and discussed. The Commission International de l'Eclairage chromaticity coordinates were found to be (0.66,0.33) for Na5Eu(WO4)(4-x)(MoO4)(x), which reaches the same level as that of the Y2O2S:Eu3+ commodity. The color-rendering index (Ra) of a typical white-light-light emitting diode (WL-LED) based on Na5Eu(WO4)(2)(MoO4)(2) was found to be 82.3, higher than that (i.e., Ra similar to 70.8) obtained for the WL-LED fabricated using the commodity of La2O2S:Eu3+ when the WL-LEDs were operated at a forward-bias current (I-f) of 20 mA at room temperature. Na5Eu(WO4)(4-x)(MoO4)(x) is therefore suggested to be a potential red-emitting phosphor for WL-LED. (c) 2008 The Electrochemical Society.