Lanthanide vanadate-based trimodal probes for near-infrared luminescent bioimaging, high-field magnetic resonance imaging, and X-ray computed tomography

We have developed a trimodal bioimaging probe for near-infrared luminescent imaging, high-field magnetic resonance imaging, and X-ray computed tomography using Dy³⁺ as the paramagnetic component and Nd³⁺ as the luminescent cation, both of them incorporated in a vanadate matrix. Among different essayed architectures (single phase and core-shell nanoparticles) the one showing the best luminescent properties is that consisting of uniform DyVO₄ nanoparticles coated with a first uniform layer of LaVO₄ and a second layer of Nd^3+-doped LaVO₄. The magnetic relaxivity (r₂) at high field (9.4 T) of these nanoparticles was among the highest values ever reported for this kind of probes and their X-ray attenuation properties, due to the presence of lanthanide cations, were also better than those of a commercial contrast agent (iohexol) commonly used for X-ray computed tomography. In addition, they were chemically stable in a physiological medium in which they could be easily dispersed owing to their one-pot functionalization with polyacrylic acid, and, finally, they were non-toxic for human fibroblast cells. Such a probe is, therefore, an excellent multimodal contrast agent for near-infrared luminescent imaging, high-field magnetic resonance imaging, and X-ray computed tomography.

Effect of Cr3+ doping on structural and optical properties of Eu3+ doped LaVO4 phosphor

In this work, the Eu³⁺, Cr³⁺ doped and co-doped LaVO₄ phosphors have been prepared through a high temperature solid-state reaction method. The powder XRD patterns of phosphors are very sharp and intense, which reflects a highly crystalline nature of phosphors. The XRD data were also refined by a Rietveld refinement method. The particle size of the phosphor samples lies in the sub-micron to micron range. The existence of La, Eu, Cr, V and O elements was verified by EDS spectra. The FTIR spectra show various absorption bands due to different vibrating groups. The optical band gap of the phosphor decreases on increasing concentration of Cr³⁺ ion. The photoluminescence excitation spectra of Eu³⁺, Cr³⁺ co-doped LaVO₄ phosphor exhibit bands due to Eu³⁺ and Cr³⁺ ions. The Eu³⁺ doped LaVO₄ phosphor exciting at 393 and 316 nm wavelengths gives intense red color at 614 nm due to the ⁵D₀ → ⁷F₂ transition of the Eu³⁺ ion. When the Cr³⁺ ion is co-doped in the Eu³⁺ doped LaVO₄ phosphor the emission spectra contain emission bands due to Eu³⁺ and Cr³⁺ ions. The emission intensity of Eu³⁺ doped phosphor reduces due to energy transfer from Eu³⁺ to Cr³⁺ ions in presence of Cr³⁺ ions upon 393 and 386 nm excitations. The lifetime of the ⁵D₀ level of Eu³⁺ ions decreases in the Eu³⁺, Cr³⁺ co-doped LaVO₄ phosphor, which also reflects the energy transfer. The Eu³⁺, Cr³⁺ co-doped LaVO₄ phosphor also produces a large amount of heat upon 980 nm excitation. Thus, the Eu³⁺, Cr³⁺ co-doped LaVO₄ phosphors may be used for LEDs, solid state lighting and heat generating devices.

Influence of Bi3+ ion on structural, optical, dielectric and magnetic properties of Eu3+ doped LaVO4 phosphor

In this paper, we have studied the structural, optical, dielectric and magnetic properties of Eu³⁺, Bi³⁺ co-doped LaVO₄ phosphors prepared by solid state reaction method. Rietveld structural analysis of the samples confirms the monoclinic crystal structure with P2₁/n space group. The particles size of Eu³⁺ doped LaVO₄ phosphor increased in presence of Bi³⁺ ion. The excitation spectrum of Eu³⁺, Bi³⁺ co-doped LaVO₄ phosphor reveals bands due to charge transfer state (CTS) and electronic transitions of Eu³⁺ and Bi³⁺ ions. The Eu³⁺ doped LaVO₄ phosphor gives intense red emission centred at 613 nm due to ⁵D₀ → ⁷F₂ transition of Eu³⁺ ion excited at 266, 355 and 394 nm wavelengths. When Bi³⁺ and Eu³⁺ ions are co-doped in the LaVO₄ phosphor the photoluminescence intensity is enhanced upto two times. The photoluminescence intensity is largest for the 266 nm excitation. This is due to energy transfer from CTS and (¹P₁, ³P₁) levels of the Bi³⁺ ion to ⁵D₄ level of the Eu³⁺ ion and increase in the particles size of phosphor. The Eu³⁺, Bi³⁺ co-doped LaVO₄ phosphors also show excellent dielectric and magnetic properties with a variation in frequency and magnetic field, respectively. Thus, the Eu³⁺, Bi³⁺ co-doped LaVO₄ phosphor may be useful in fabricating displays devices, red emitting phosphors, dielectric capacitors and magnetic devices.