Study of (La, Gd)OCl:Eu3+ phosphors for WLEDs application: photoluminescence and Judd-Ofelt analysis

A series of layered La1-x-yGdxEuyOCl (x = 0, 0.25, 0.50, 0.75, 0.99; y = 0.01) phosphors were synthesised by the conventional solid-state method at 700 degrees C for 2 h. When x = 0.00 and 0.99, the phosphors were crystallised in the tetragonal structure with space group P4/nmm (No. 129). On increasing Gd3+ ion concentration in Eu3+ activated LaOCl system, GdOCl phase starts appearing. Field emission scanning electron microscopy (FE-SEM) revealed that the particles were agglomerating and form spherical-like morphology. The photoluminescence (PL) spectra reveal that the relative intensity of D-5(0) -> F-7(2) transition (619 nm) increases with increase in the Gd3+ ions. This was owing to the property of Gd3+ ions to act as an intermediate sub lattice to facilitate the energy transfer to Eu3+ ions. Intensity parameters and radiative properties such as transition probabilities, radiative lifetime and branching ratio were calculated using the Judd-Ofelt theory. The CIE colour coordinates of Gd0.99Eu0.01OCl phosphor are close to the commercial Y2O3: Eu3+, Y2O2S: Eu3+ and National Television System Committee (NTSC) red phosphor. The results indicate that the quality of red colour production is suitable for white LEDs applications