Effect of Molten Salt Synthesis Processing Duration on the Photo- and Radioluminescence of UV-, Visible-, and X-ray-Excitable La₂Hf₂O₇:Eu³⁺ Nanoparticles

Abstract

Ln 3+ -ion-doped nanomaterials possess excellent properties because of their high color purity, longer excited state lifetime, narrow emission, and large Stokes shifts. In this work, we studied the correlation between the luminescence properties of La 2 Hf 2 O 7 :Eu 3+ pyrochlore nanoparticles (NPs) synthesized by a molten salt synthesis (MSS) method at a relatively low temperature and several MSS processing durations (from 1 to 12 h). We synthesized these NPs with different sizes just by changing the MSS processing time without subjecting to high temperature. Raman spectroscopy confirmed the stabilization of the ideal pyrochlore structure of the La 2 Hf 2 O 7 :Eu 3+ NPs at various MSS processing durations. The synthesized NPs exhibited bright red emission under UV, visible, and X-ray excitations, highlighting their potential applications as a red phosphor and scintillator. As the MSS processing time was increased from 1 to 12 h, a spectral change in the position of the charge transfer state in the La 2 Hf 2 O 7 :Eu 3+ NPs was observed. The sample processed by the MSS with a duration of 3 h exhibited the highest luminescence intensity, which was attributed to its optimum crystals with least surface defects and less agglomeration. The obtained results strongly and unambiguously indicate the brighter side of this new type of pyrochlore-based NPs in the fast growing field of solid-state lighting and scintillator materials.

On comparison of luminescence properties of La2Zr2O7 and La2Hf2O7 nanoparticles

“…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 .…”

“…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. 11,12,[36][37][38][39] 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. 40 From these studies, we found that the La 2 Hf 2 O 7 -based NPs display better luminescence and scintillation performance compared to the La 2 Zr 2 O 7 NPs, but could not understand the underlying reasons for their luminescence differences.…”

Luminescent PVDF nanocomposite films and fibers encapsulated with La2Hf2O7:Eu3+ nanoparticles

“…We also want to emphasize here that photophysical properties of pristine LHOE powder NPs published before [5,7,21] looks very similar to that of film in terms of emission bandwidth and asymmetry ratio. Only difference is increase in stark component of MDT to 3 in film compared 2 in pristine powder.…”

“…Some of the favorable properties include excellent dielectric properties due to its small number of defect densities, ability to accommodate large concentration of dopant both at A and B sites with a general formula of A 2 B 2 O 7 , wide bandgap, moderate phonon E = 745 cm −1 and high stopping power for X-and γ-rays with Z Hf = 72, and high density of 7.9 g/cm 3 . [19][20][21] We have done extensive work on red-emitting La 2 Hf 2 O 7 :Eu 3+ (LHOE) down-converting nanoparticle (NP) powders for several applications in the areas of phosphors, scintillators, thermographic phosphors, etc. [5,7,21].…”

“…[19][20][21] We have done extensive work on red-emitting La 2 Hf 2 O 7 :Eu 3+ (LHOE) down-converting nanoparticle (NP) powders for several applications in the areas of phosphors, scintillators, thermographic phosphors, etc. [5,7,21].…”