Correlating Structure and Luminescence Properties of Undoped and Eu³⁺-Doped La₂Hf₂O₇ Nanoparticles Prepared with Different Coprecipitating pH Values through Experimental and Theoretical Studies

Abstract

Understanding the structure-property relationship and optimizing properties of phosphors for use in lighting and scintillation fields is an important materials challenge. In this work, we investigated the effects of the pH value of the coprecipitating solution adjusted by the concentration of NHOH(aq) on the structure and optical properties of the obtained LaHfO nanoparticles (NPs). The obtained NPs stabilize in the ideal pyrochlore structure, but the extent of ordering increased with an increase in the pH value used. The NPs prepared at pH = 12.1 displayed the best optical performance owing to the balance of the crystallinity, agglomeration, and surface defects. On the basis of density functional theory (DFT) calculations, the origin of violet-blue emission in undoped LaHfO NPs was attributed to defect states in the electronic band gap arising due to oxygen defects. For the LaHfO:Eu NPs, the Eu dopants possess low symmetry and their occupancy is more favorable at the LaO site. DFT calculations further justify the complete host-to-dopant energy transfer and origin of the most intense red emission observed experimentally. Understanding the interplay of the experimental and theoretical results thus is a very useful general approach for improving the efficiency of luminescent materials.

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

“…Several parameters affect the morphology and size of NPs synthesized by the molten salt method. In our previous investigation, we demonstrated that the level of OH − concentration during the synthesis of the precursor affects the size of the synthesized NPs without manipulating the molten salt synthesis time and temperature [7]. For the LHOE system, as the concentration of OH − increased, the size of the particles increases proportionally [7].…”

“…N, N-Dimethylacetamide (DMA, ≥ 99%), acetone (≥ 99.5%), PVDF (average molecular weight of 534,000) were purchased from Sigma-Aldrich USA. The LHOE NPs were synthesized by a molten salt method as reported in our previous publications [5][6][7]10]. 1.0 wt% of LHOE NPs and 22wt%of PVDF were mixed in a 77 wt% solvent (50:50 weight percentage ratio of acetone: DMA) by stirring with a magnet bead for 2 h. The LHOE-PVDF nanocomposite films were fabricated through a drop-casting technique by dropping 1 mL of the solution on a planar surface of a watch glass.…”

“…In our previous investigation, we demonstrated that the level of OH − concentration during the synthesis of the precursor affects the size of the synthesized NPs without manipulating the molten salt synthesis time and temperature [7]. For the LHOE system, as the concentration of OH − increased, the size of the particles increases proportionally [7]. In the present study, the LHOE NPs were synthesized using a 10% NH 4 OH aqueous solution, which agrees with the correlated size revealed by the SEM image analysis, Fig.…”

“…For the same reason, they have been getting significant attention for applications in solid-state lighting, scintillators, thermal sensor, pressure sensor, bioimaging, catalysis, biosensor, photodynamic therapy, fingerprint imaging, etc. [1][2][3][4][5][6][7][8][9]. Synthesis of LNPs plays a vital role in deciding its optimal usage and designated field [10].…”

“…[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].…”