Observation of up conversion/down conversion luminescence and structural analysis of La2Zr2O7: Pr3+ nano phosphors

Charge transfer band (CTB) transition significantly improves the photoluminescence properties of phosphor materials due to its higher absorption efficiency than the characteristic excitations of rare-earth ions. La2Zr2O7 (LZO): Pr3+ phosphors with varying doping concentrations of Pr3+ were synthesized through the hydrothermal method. The formation of the pure pyrochlore phase was confirmed from powder X-ray diffraction (XRD). The structural analysis was performed from Rietveld refinement of the XRD data. Field emission electron microscope (FESM) equipped with EDX spectroscopy was used to study the surface morphology and elemental compositions. X-ray photoelectron spectroscopy (XPS) analysis of the optimized sample provides the bonding state of the compositions. Under 257 nm CTB excitation, the photoluminescence emission spectra (PL) exhibit all the characteristic emission peaks of Pr3+ ion. The transitions involved in the excitation and emission process have been shown in the energy level diagram of Pr3+ ions. The Concentration quenching effect was explained from Bless relation and Dexter energy transfer theory between activator ions. Decay curves of the prepared phosphors show bi-exponential behavior. The up-conversion emission spectra were recorded under 980 nm laser excitation. The optical transition in the UV-Vis range was investigated based on the diffuse reflectance spectra, and the results match well with the excitation spectra. The photometric study informs the color and the quality of the emitted light. The outcomes produce a new synthesis method to prepare La2Zr2O7:Pr3+ nano phosphor that can be an excellent candidate for solid-state lighting and UV/NIR to the visible converter in solar cell applications.