Luminescence properties of La2W2−xMoxO9 (x = 0–2):Eu3+ materials and their Judd–Ofelt analysis: novel red line emitting phosphors for pcLEDs
A series of novel red emitting La1.95Eu0.05W2−xMoxO9 (x = 0–2, in steps of 0.1) and La2−yEuyW1.6Mo0.4O9 (y = 0–2, insteps of 0.2) phosphors were prepared by a conventional solid state reaction. Powder XRD analysis of La1.95Eu0.05W2−xMoxO9 (x = 0–2, in steps of 0.1) reveals a phase transition from a triclinic to a cubic structure with increasing Mo6+ concentration (x ≥ 0.2). All the compositions show a broad charge transfer (CT) band due to CT from O to W/Mo and red emission (due to Eu3+ ions). In order to obtain the strongest red emission, concentration variation of Eu3+ was performed in La2−yEuyW1.6Mo0.4O9 (x = 0–2, insteps of 0.2). The Eu1.6La0.4W1.6Mo0.4O9 composition shows a high red emission intensity (∼8.2 times) compared to a commercial red phosphor with very good CIE chromaticity coordinates (x = 0.67, y = 0.33). A selected composition has also been synthesized by simple co-precipitation method. The emission intensity of the Eu1.6La0.4W1.6Mo0.4O9 phosphor synthesized by co-precipitation technique is ∼1.78 times higher than that of the phosphor synthesized by the solid state reaction. Phonon sideband spectrum analysis has been carried out for Eu3+ activated La2M2O9 (M = W and Mo). The temperature dependent photoluminescence studies reveal that the Eu1.4La0.6W1.6Mo0.4O9 compositions loses 30% of its efficiency up to 400 K (compared to ∼80% for CaS:Eu2+) and the Judd–Ofelt parameters were also calculated for the Eu3+ ions.