Exploring the effect of boron on the grain morphology change and spectral properties of Eu3+ activated barium tantalate phosphor

The effect of the grain morphology on the photoluminescence, charge transfer band, and decay properties was investigated by xEu3+, yB3+ (x = 10 mol%, y = 0, 5, 15, 30, 50, 70, and 100 mol%) co-doped BaTa2O6 ceramics fabricated by solid-state reaction. X-ray diffractions of the samples showed that the single-phase structure persisted up to 100 mol% and there was an improvement in crystallinity with increasing B3+ concentration. SEM micrographs of the Eu3+, B3+ co-doped grains showed that the flux effect of boron promotes grain growth and elongated grain shape. The PL emissions of the BaTa2O6:xEu3+, yB3+ co-doped phosphors increased up to 100 mol% B3+ concentration, and there was an increase in the intensities of the CTB energy 5D0 → 7F1 transition. The increase in PL may be attributed to the increased grain size leading to a decrease in the surface area (SA)/volume (vol) ratio with increasing B3+ concentration, as well as the improvement in crystallinity. However, the decrease in asymmetry ratio was related to the occupation of centrosymmetric (B) sites and the transformation from a rounded/irregular-like to an elongated/rod-like grain shape which has an increasing effect on the SA/vol ratio. The decreasing trend of the Judd-Ofelt parameters (Ω2, and Ω4) with the increase in boron was related to a high local symmetry of Eu3+ sites, and an increase in the electron density of the surrounding ligands, respectively. The increase in boron led to longer decays in the observed lifetime with bi-exponential characteristics. The CIE diagram and UV lamp photographs of the phosphors showed a color transition from red to orange associated with the increasing magnetic dipole transition. This study may provide an alternative perspective and new strategies to describe the control of grain morphology and luminescence concerning RE-doped phosphors.

Luminescence investigation of red-emitting Sr2MgMoO6:Eu3+ phosphor for visualization of latent fingerprint

Fingerprints are widely studied due to their unique shape and lifelong properties. The latent fingerprint (LFP) visualization is critical in identifying crime scenes and personal information. At present, the powder dusting method for LFP detection is favored due to its environmental friendliness and nontoxicity. However, this method has low resolution, low sensitivity, and large background interference. To address these shortcomings, the red-emitting Sr₂MgMoO₆:xEu³⁺ (x = 0-0.50) phosphors were synthesized using the solid-state reaction process. The products were systematically studied through the structural phase, luminescent property, decay curve, and color purity. Sr₂MgMoO₆:xEu³⁺ phosphors were monitored at 596 nm and exhibited a commendable broad excitation band between 250 and 475 nm. This result indicated that the disadvantage of the poor absorption of commercial red phosphors (Y₂O₂S:Eu³⁺) in the near-ultraviolet region was overcome. Under excitation at 393 nm, the synthesized Sr₂MgMoO₆:Eu³⁺ phosphor exhibited intense red light at 596 and 616 nm, due to the ⁵D₀ → ⁷F₁ and ⁵D₀ → ⁷F₂ transitions of Eu³⁺ ions. The optimal concentration for the Sr₂MgMoO₆:xEu³⁺ phosphor was x = 20 mol%, and the concentration quenching effect was ascribed to the dipole-dipole interaction. The Commission International del'Eclairage (CIE) chromaticity coordinates of Sr₂MgMoO₆:Eu³⁺ were (0.643, 0.356), and the color purity was 99.8%. Furthermore, the fluorescent LFP images developed by Sr₂MgMoO₆:0.20Eu³⁺ phosphors were well visualized, and level 1-3 details were well identified with high resolution, contrast, sensitivity, and selectivity. The obtained results suggested that the Sr₂MgMoO₆:Eu³⁺ phosphor can be applied for LFP detection.

Stabilizing the B-site oxidation state in ABO3 perovskite nanoparticles

The stabilization of the B-site oxidation state in ABO3 perovskites using wet-chemical methods is a synthetic challenge, which is of fundamental and practical interest for energy storage and conversion devices. In this work, defect-controlled (Sr-deficiency and oxygen vacancies) strontium niobium(iv) oxide (Sr1-xNbO3-δ, SNO) metal oxide nanoparticles (NPs) were synthesized for the first time using a low-pressure wet-chemistry synthesis. The experiments were performed under reduced oxygen partial pressure to prevent by-product formation and with varying Sr/Nb molar ratio to favor the formation of Nb4+ pervoskites. At a critical Sr to Nb ratio (Sr/Nb = 1.3), a phase transition is observed forming an oxygen-deficient SrNbO3 phase. Structural refinement on the resultant diffraction pattern shows that the SNO NPs consists of a near equal mixture of SrNbO3 and Sr0.7NbO3-δ crystal phases. A combination of Rietveld refinement and X-ray photoelectron spectroscopy (XPS) confirmed the stabilization of the +4 oxidation state and the formation of oxygen vacancies. The Nb local site symmetry was extracted through Raman spectroscopy and modeled using DFT. As further confirmation, the particles demonstrate the expected absorption highlighting their restored optoelectronic properties. This low-pressure wet-chemical approach for stabilizing the oxidation state of a transition metal has the potential to be extended to other oxygen sensitive, low dimensional perovskite oxides with unique properties.

Synthesis and Rational design of Europium and Lithium Doped Sodium Zinc Molybdate with Red Emission for Optical Imaging

Highly efficient fluorescent and biocompatible europium doped sodium zinc molybdate (NZMOE) nanoprobes were successfully synthesized via Polyol method. Non-radiative defect centres get reduced with Li+ co-doping in NZMOE nanoprobes. XRD spectra and Rietveld refinement confirmed successful incorporation of lithium ion and crystallinity was also improved with Li+ co-doping. The shape of phosphor is rod shaped, as determined by TEM. Significant enhancement in photoluminescence intensity was observed with 266, 395 and 465 nm excitations. Profound red emission was recorded for 5 at% Li+ co-doped NZMOE nanoprobes with 266 nm excitation. It shows high asymmetry ratio (~15), color purity (94.90%) and good quantum efficiency (~70%). Judd Ofelt parameters have been calculated to measure intensity parameters and radiative transition rates. In order to measure biocompatibility of the nanoprobes, cytotoxicity assays were performed with HePG2 cells. The fluorescence emitted from phosphor material treated HePG2 cells was also measured by Laser Scanning Confocal Microscopy. The bright red fluorescence in HePG2 cells treated with very low concentration (20 μg/ml) of phosphor material indicates that it could be a promising phosphor for biological detection or bio-imaging.