Investigation On The Structure And Photoluminescence Properties Of PVP Capped Mgal2o4:Tb3+ Doped Nanophosphors

The demand for highly luminescent nanophosphors for high resolution displays and lighting with high energy saving capability are potentially important due to their numerous advantageous properties such as long lifetime, high energy efficiency, better quantum yield, better reliability and environmentally friendly characteristics. Rare earth incorporated nanophosphors have opened up exciting avenues for new applications across various fields. Spinel oxides with general formula, AB2O4 are indeed known for their thermal and chemical stability. Magnesium aluminate (MgAl2O4) is a well known spinel material that has been extensively used as the host material for developing phosphors due to their range of excellent properties such as low density, high melting point, good resistance against chemical attacks and excellent strength at high temperatures. In the present study, green light emitting Mg1-xTbxAl2O4 (x = 0.02, 0.04, 0.06, 0.08 and 0.10) nanophosphors have been synthesized by polyvinylpyrrolidone (PVP) polymer capped citrate nitrate sol-gel method. The effect of Tb3+ doping on the structural and luminescent characteristics of the prepared nanophosphors were examined using a variety of characterization techniques such as X- ray diffraction (XRD), Transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), UV-diffuse reflectance (DRS) and Photoluminescence (PL) spectroscopy. X-ray diffraction and transmission electron microscopic techniques reveal the structural characteristics of the prepared samples. UV visible diffuse reflectance spectra were employed to find the optical band gap of the samples by utilising the Kubelka-Munk function. Fourier transform infrared spectra provided information about various functional groups present in the samples. Photoluminescence excitation and emission spectra as well as lifetime measurements were used to analyse the luminescence dynamics of the prepared nanophosphors. Photoluminescence emission spectra comprised of two regions, characteristic of blue emissions and green emissions corresponding to 5D3→7FJ (J=5, 4, 3) transitions and 5D4→7FJ (J=6, 5, 4, 3) transitions respectively. Increase in the Tb3+ ion concentration lead to concentration quenching phenomenon which can be interpreted by evaluating the critical distance between the dopant ions and confirmed that phonon-assisted multipole-multipole interaction is the mechanism behind energy transfer process. Dexter’s theory further concluded that the interaction involved among Tb3+ ions is dipole-dipole in nature. Evaluation of photometric parameters such as CIE co-ordinates, correlated colour temperature and colour purity indicates that the obtained phosphors can serve as promising materials for solid state lighting as well as for optoelectronic applications specifically for white LEDs.