Alkaline earth metal tungstate compounds activated by trivalent europium (Eu3+) are promising candidates for narrow spectral emission red phosphors suitable for high efficacy white light emitting diodes (LEDs). By growing crystals of these compounds from high temperature flux containing Na+ as the charge compensation element, enhancement in the emission intensity of A1 − xWO4: (A = Mg, Ca, Sr) has been demonstrated compared to phosphor powders synthesized using traditional solid state reaction. An optimum flux to solute ratio of 1.5:1 resulted in the largest size crystals using the sodium tungstate flux at growth temperature around 1300 °C. Amongst the three compounds studied, calcium tungstate exhibited the highest luminescence and magnesium tungstate the lowest. These results have been explained by the differences in the ionic radii of the cations compared to the europium activator and the energy bandgap of the host lattice.
CaWO4:Eu3+/Na+ flux grown phosphor crystals exhibit almost five times higher emission intensity as compared to phosphor powders synthesized by solid-state reaction.