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A series of 5mol% Eu 3+ doped rare earth (RE) hafnium oxide RE 2 Hf 2 O 7 (RE = Y, La, Pr, Gd, Er, and Lu) nanoparticles (NPs) have been synthesized, calcinated, and systematically investigated using X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and optically excited luminescence. Effects of the A-site RE 3+ cation and calcination on the crystal structure of the RE 2 Hf 2 O 7 :5%Eu NPs were distinguished using XRD and Raman studies.Spectroscopic analysis showed that the La 2 Hf 2 O 7 :5%Eu 3+ and Pr 2 Hf 2 O 7 :5%Eu 3+ possessed ordered pyrochlore structures while the RE 2 Hf 2 O 7 :5%Eu 3+ compositions (RE = Y, Er, and Lu) possessed disordered fluorite structure and were thermodynamically stable up to the highest calcination temperature employed in this study (1500°C). However, a disordered-ordered transition observed in the Gd 2 Hf 2 O 7 :5%Eu 3+ composition indicated that it was not thermodynamically stable. Detailed photoluminescence (PL) studies, including quantum yield and decay properties of each sample before and after calcination, were performed and correlated with their compositions and crystal structures. These results suggest that the A site RE 3+ cations and calcination of these RE 2 Hf 2 O 7 :5%Eu NPs play important roles in their PL properties.

There is an increasing interest in rare earth (RE) doped nanoparticles (NPs) due to their sharp absorption and photoluminescence (PL) in the near infrared (NIR) spectral region. These NIR based nanoparticles (NPs) could allow biological imaging at substantial depths with enhanced contrast and high spatial resolution due to the absence of auto fluorescence in biological samples under infrared excitation. Here, we present the highly efficient infrared photoluminescence in GdF3:Nd3+ nanoparticles under 800 nm excitation within the hydrodynamic size limitations for bio-applications. The downconversion (Stokes emission) absolute quantum yield (QY) measurements in powder, poly maleic anhydride- alt-1- octadicene (PMAO) coated powder and colloidal solutions have been investigated. QY measurements have revealed that downconversion(Stokes emission)QY in an average 5 ± 2 nm sized GdF3: 1% Nd3+colloidalNPs are 2000 times higher than efficient upconversion (UC) particles NaYF4: 20 % Er/ 2% Yb of same size. Furthermore, the utility of these NIR emitting nanoparticles forbioimagingprobe has been demonstrated by confocal imaging and spectroscopic study.

This study presents the structural, optical, and radioluminescent characterization of newly synthesized europium-doped lanthanum hafnate (La 2 Hf 2 O 7 :xmol%Eu 3+ , x = 0 to 35) nanoparticles (NPs) for use as phosphors and scintillation materials. Samples prepared through a combined co-precipitation and molten salt synthetic process were found to crystalize in the pyrochlore phase, a radiation tolerant structure related to the fluorite structure. These samples exhibit red luminescence under ultraviolet and X-ray excitation. Under these excitation wavelengths, the optical intensity and quantum yield of the La 2 Hf 2 O 7 :xmol%Eu 3+ NPs depend on the Eu 3+ concentration and are maximized at 5%. It is proposed that there is a trade-off between the quenching due to defect states/crossrelaxation and a high dopant concentration. An optimal dopant concentration allows La 2 Hf 2 O 7 :5mol%Eu 3+ NPs to show the best luminescent properties of all the samples.

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New optical material of La2Hf2O7:Pr3+ nanoparticles with efficient luminescence and scintillating properties have drawn a great deal of attention due to the demand for optoelectronic devices and medical theranostics.