Structural and photoluminescence studies of LaNbO4:Er3+ phosphors synthesized via citric based sol-gel route for WLED applications

Abstract

A series of Er³⁺ activated LaNbO₄ phosphor were synthesized via citric sol-gel method. The structural, elemental and morphological investigations were done by XRD, FTIR, EDS, SEM and TEM analysis. Structural studies confirm the monoclinic phase of the phosphor and micro structure nature of the samples were analyzed by SEM and TEM analysis. UV–Vis–NIR optical absorption spectrum of La_0.99NbO₄:0.01Er³⁺ phosphor was analyzed on the basis of Judd-Ofelt theory and radiative properties were calculated using JO intensity parameters. The energy transfer from host to Er³⁺ ions were studied at host excitation of 251 nm. Under 379 nm excitation of Er³⁺ ions, LaNbO₄:Er³⁺ phosphors emit intense green light due to transitions ²H_11/2 → ⁴I_15/2 and ⁴S_3/2 → ⁴I_15/2. NIR photoluminescence spectra were measured and intense near infrared emission at 980 nm (⁴I_11/2 → ⁴I_15/2) and 1535 nm (⁴I_13/2 → ⁴I_15/2) were observed under 800 nm excitation. Upconversion fluorescence properties of La_1-xNbO₄:xEr³⁺ phosphors have also been studied at 980 nm excitation and three strong emissions were observed around 529 nm (²H_11/2 → ⁴I_15/2), 551 nm (²S_3/2 → ⁴I_15/2) and 668 nm (⁴F_9/2 → ⁴I_15/2). CIE chromaticity studies were done for both downconversion and upconversion fluorescence. The samples are exhibiting yellowish green emission under both 379 nm and 980 nm excitations and the corresponding CCT values and color purity were also calculated.