Recently, there has been a great amount of interest in dioxide (MO2, M = Zr, Ce, and Hf) derivative structures, such as A2M2O7 type compounds, due to their binary metal cation (A) sites which can be readily replaced with trivalent RE ions. Correspondingly these materials have wide technological applications, including hosts of optical active centers, solid electrolytes in solid oxide fuel cells, neutron absorbing materials, nuclear waste storage materials, thermal barrier coatings (TBCs). In this study, we explored the nanoparticles of Pr3+ doped La2Hf2O7 pyrochlore (LPHP) as a new downconversion materials for possible applications in optoelectronics. La2Hf2O7:xmol%Pr3+(x = 0, 0.1, 0.2, 0.3, 0.5 and 1.0) were synthesized using molten salt synthesis and characterized systematically using XRD, Raman, FTIR, XPS techniques. Photophysical properties were probed using time resolved photoluminescence. The emission spectrum shows two dominant peaks arising from a 3P0-3H4 transition in the blue-green region and 1D2-3H4 transition in the red region. Concentration quenching was observed at a very low Pr3+ concentration of 0.2 mol%, which is mainly due to a non-radiative energy transfer mediated by dipole–dipole interaction caused by the accumulation of Pr3+ ion at nanocrystal periphery that provides the relaxation of lattice strain arising from the differences of ionic size and charge of Pr3+ and La3+/Hf4+. Furthermore, the fast decaying Pr3+ (170-310 µs) arises because of Pr3+ ions occupying Hf4+ site whereas slow decaying species (570-960 µs) can be attributed to Pr3+ ions occupying La3+. Quantum yield (QY) measurement reflected that 0.1 mol % doped LPHP NPs have high value of 20.54%. Our study suggested a new Pr3+ based reddish-orange emitting material with relatively high luminescence lifetime and QY can be used for phosphor materials as well as in medical diagnostics where higher lifetimes are desirable. However, the host lattice needs to be modified so that higher concentration of dopant ion can be accommodated and also one need to think on improving the green emission from 3P0 states for scintillator applications.

Molten state synthesis of Pr3+ activated lanthanum hafnate nanoparticles as potential downconversion phosphor

255th National Meeting (2018)

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