Spectroscopic Studies of Nanopowder and Nanoceramics La2Hf2O7:PrLa_2 Hf_2 O_7:Pr Scintillator

Sintered nanoceramics of Pr-doped lanthanum hafnate, $La_{2}Hf_{2}O_{7}:Pr$, were prepared by means of a high-pressure sintering technique using nanopowders made by Pechini method. Structure, morphology, and spectroscopic properties of the ceramics compared to the starting powder are presented and discussed. Emission and excitation spectra recorded at room temperature as well as at 7 K using synchrotron radiation are presented together with results of luminescence kinetics measurements. In ceramics, at 7 K, the $Pr^{3+}$ luminescence from $^{3}P_{0}$ (blue-green, green, and red region) and $^{1}D_{2}$ (red) levels is accompanied by a broad-band emission located in the 380–530 nm range of wavelengths, whereas powders gives only the $Pr^{3+}$-related luminescence. Depending on the excitation wavelength, the broad-band emission maximum moves between 430 and 470 nm indicating superposition of at least two components. In sintered nanoceramics, the lifetimes of $Pr^{3+}$ emissions from $^{3}P_{0}$ and $^{1}D_{2}$ levels were by 10%–20% shorter compared to the powder. The existence of different luminescence centers was proved by the selective emission decays examination. The fast 5$\mathit{d}$ $\rightarrow$ 4$\mathit{f}$ luminescence of $Pr^{3+}$ was not observed from either of the two types of $La_{2}Hf_{2}O_{7}:Pr$ materials

Nano- and Microcrystalline Lu_2O_3:Eu Phosphors: Variations in Occupancy of C_2 and S_6 Sites by Eu^(3+) Ions

The occupancy of C-2 and S-6 sites by Eu3+, ions in nanocrystalline powders and microcrystalline ceramics of Lu2O3 prepared from these powders was studied by Mossbauer spectroscopy. It was proved that in nanopowders prepared by vigorous combustion syntheses the occupancy of the C-2 and S-6 sites by Eu3+, is almost random, with only a very limited preference for the former. For ceramic specimens formed at 1750 degrees C within a few hours, it was found that Eu3+ ions strongly prefer to enter the Lu2O3 host at the C-2 site. We concluded that thermodynamically the non-centrosymmetric site C-2 is preferred to the S-6 site by Eu3+. However, if the formation of crystallites is very fast, like in combustion syntheses, the Eu3+ ions are entrapped into the two sites nearly randomly