Structural, photoluminescence and radioluminescence properties of Eu3+ doped La2Hf2O7 nanoparticles

Abstract

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.

Nanoparticles to mediate X‐ray‐induced photodynamic therapy and Cherenkov radiation photodynamic therapy

“…While the aforementioned principles still apply, nanoparticle scintillators have their own sets of rules for synthesis and luminescent properties. Nanomaterials have expanded the possibilities for X-ray luminescence uses in high-energy physics and medical imaging, providing a large portfolio of compositions including composite films, vitroceramics, thin films, coordination compounds, metal-organic frameworks (MOFs), and organic-inorganic hybrid materials (Cooper, Bekah, & Nadeau, 2014;Hamieh, Dorkenoo, Taupier, Henry, & Halley, 2017;Pereira, Martin, Levinta, & Dujardin, 2015;Vistovskyy et al, 2014;Vistovskyy et al, 2016;Wahid, Pokhrel, & Mao, 2017). Even pure metals and semiconductors, which usually do not function as X-ray scintillators, may function as such if formed into nanoparticles (Brus, 1984;Paillard et al, 1999;Yuan et al, 2013).…”

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, magnetic materials, electrocatalysis, sensors, optical materials, solid‐oxide fuel cells, high level nuclear waste hosts, etc. Moreover, recently relevant nanostructured pyrochlore materials have gained significant attention compared with their bulk counterparts in the areas of photoluminescence, scintillation, and magnetism …”

“…Recent studies on zirconate based phosphors show that, Zr 4+ exists in d 0 configuration play a very decisive role in ligand to metal charge transfer (LMCT) . 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 …”

“…The photophysical properties of luminescent Eu 3+ ions are strongly governed by the local environment, which depends on the crystal field surrounding the emitting ion. In our earlier work, we focused on separate exploration of the effect of Eu 3+ doping concentration, effect of molten salt processing time, effect annealing temperature, effect of co‐precipitating pH on the emission output, quantum efficiency, radioluminescence output and excited state lifetime of La 2 Zr 2 O 7 and La 2 Hf 2 O 7 NPs . Molten salt synthesis has several advantages for an unique materials synthesis method, such as low formation temperature, environment benignness, simple to operate in normal research laboratory, easy to scale up, and cost efficient .…”

“…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.…”