Systematic Studies on RE₂Hf₂O₇:5%Eu³⁺ (RE = Y, La, Pr, Gd, Er, and Lu) Nanoparticles: Effects of the A-Site RE³⁺ Cation and Calcination on Structure and Photoluminescence

Abstract

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.

Nanoscale insights into doping behavior, particle size and surface effects in trivalent metal doped SnO2

“…5) and those of the II – IV centers. Next, the absence in the Raman spectra of the strongest characteristic phonon mode of stannate pyrochlore (around 510 cm −1   67 ) along with the strongly dissimilar emission exhibited by Eu 2 Sn 2 O 7 68–70 grown by us using a sol-gel method 71 (also included in Fig. 5 as orange spectrum) to Eu centers II – IV dismiss the occurrence of this phase in our samples.…”

On comparison of luminescence properties of La2Zr2O7 and La2Hf2O7 nanoparticles

“…These properties make them suitable for scientific and technological applications such as thermal barrier coatings, 1 magnetic materials, 2,3 electrocatalysis, 4,5 sensors, 6 optical materials, 7 solid-oxide fuel cells, 8 high level nuclear waste hosts, 9 etc. Moreover, recently relevant nanostructured pyrochlore materials have gained significant attention compared with their bulk counterparts in the areas of photoluminescence, [10][11][12][13] scintillation, [11][12][13] and magnetism. 14 In this context, La 2 Zr 2 O 7 and La 2 Hf 2 O 7 have been two standout pyrochlores for their suitability in various kinds of technological applications such as luminescence, scintillator, ferroelectric material, nuclear waste host, catalyst, and electrode material in fuel cells, etc.…”

“…34 There are only a few independent reports on the luminescence studies of La 2 X 2 O 7 :Eu 3+ (X = Zr and Hf), but comparative studies for the observed differences are missing, not to mention the understanding of the underlying mechanisms both experimentally and theoretically, including the energetics of ionized oxygen vacancies, the host to dopant energy transfer, and non-radiative channels. [10][11][12]22,23 Doping host materials is an efficient way to synthesize tunable luminescent phosphors. Moreover, doping can shift the light emission from undoped La 2 B 2 O 7 (B = Zr and Hf) NPs to other regions.…”

Molten-Salt Synthesis of Complex Metal Oxide Nanoparticles

“…The formation of nanomaterials is ultimately governed by the melting point of salts used as molten solvents, such as alkali chloride, sulfate, carbonate, or hydroxide 1,6,31,32 . It has been reported that the use of different molten salts can modify the formation temperature, thereby altering the particle size and morphology 18 .…”

“…Generalizability: The MSS method is also a generalizable technique to produce nanoparticles with various compositions. Other than simple metal oxides and some fluorides, nanomaterials of complex metal oxides that have been successfully synthesized by the MSS method include perovskites (ABO 3 ) 10,11,12,13,14 , spinel (AB 2 O 4 ) 15,16 , pyrochlore (A 2 B 2 O 7 ) 4,17,18,19 , and orthorhombicstructures (A 2 B 4 O 9 ) 2,3,20 . More specifically, these nanomaterials include ferrites, titanates, niobates, mullite, aluminium borate, wollastonite, and carbonated apatite 7,9,21 .…”