Tuning of Photoluminescence in pH-Dependent Tb - doped LaPO₄

Tb³⁺ doped LaPO₄ nanophosphors were synthesised by using simple co precipitation method in deionised water at various pH values of the precursor solutions (1, 3,4, 6, and 9) keeping concentration as constant. The synthesised samples were characterized by X-ray diffraction (XRD), Fourier Transform Infrared (FTIR) Spectroscopy, Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Energy dispersive X-ray Analysis (EDX) and Photoluminescence (PL) Studies. X-ray diffraction studies indicated a reduction in size beyond pH = 4, which is in close agreement with TEM images. The crystallinity index calculation from XRD showed that the crystallinity of Tb³⁺ doped LaPO₄ increased and then decreased beyond pH value of 4. The photoluminescence studies (PL) also show that there were increased in the intensity with rise in pH values and then decreased at higher pH value which may be due to change in crystallinity, surface defect and also with the quenchers (H⁺, OH^- )concentrations. TEM and SEM images of the nanophosphors reveal nanorods structure. The functional groups and elemental composition of the nanoparticles were studied using FTIR and EDX. The samples appeared greenish blue colour when exposed to UV lamp, thus, it can be used in display, lighting, sensor or bioimaging.