Assessment of NIR-triggered PEG-coated NaGdF4:Tm3+/Yb3+bio-compatible upconversion nanoparticles for contrast enhancement in OCT imaging and optical thermometry.

In this investigation, we embarked on the synthesis of polyethylene glycol coated NaGdF4:Tm3+/Yb3+upconversion nanoparticles (UCNPs), aiming to assess their utility in enhancing image contrast within the context of swept source optical coherence tomography (OCT) and photo-thermal OCT imaging. Our research unveiled the remarkable UC emissions stemming from the transitions of Tm3+ions, specifically the1G4→3H6transitions, yielding vibrant blue emissions at 472 nm. We delved further into the UC mechanism, meticulously scrutinizing decay times and the nanoparticles' capacity to convert radiation into heat. Notably, these nanoparticles exhibited an impressive photo-thermal conversion efficiency of 37.5%. Furthermore, our investigations into their bio-compatibility revealed a promising outcome, with more than 90% cell survival after 24 h of incubation with HeLa cells treated with UCNPs. The nanoparticles demonstrated a notable thermal sensitivity of 4.7 × 10-3K-1at 300 K, signifying their potential for precise temperature monitoring at the cellular level.

NaYF4:Ho3+/Yb3+@NaGdF4 core@shell upconversion nanoparticles for contrast enhancement in bimodal in-vitro OCT imaging.

Contrast enhancement is explored in optical coherence tomography images using core NaYF4:Ho3+/Yb3+ and core@shell NaYF4:Ho3+/Yb3+@NaGdF4 nanoparticles. Under 980 nm excitation, core@shell nanoparticles exhibited 2.8 and 3.3 times enhancement at 541 nm and 646 nm emission wavelengths of Ho3+ ions compared to core nanoparticles. Photo-thermal conversion efficiencies were 32% and 20% for core and core@shell nanoparticles. In swept-source optical coherence tomography (SSOCT), core@shell nanoparticles have shown superior contrast, while in photo-thermal optical coherence tomography (PTOCT) core nanoparticles have excelled due to their higher photo-thermal conversion efficiency. The enhancement in contrast to noise ratio obtained is 58 dB. Comparative assessments of scattering coefficients and contrast-to-noise ratios were conducted, providing insights into nanoparticle performance for contrast enhancement in optical coherence tomography.

Exploring the Effect of Size Variability on Efficiency of Upconversion Nanoparticles as Optical Contrast Agents.

The current works explores the optical contrast property and nanaotheranostic capabilities of the rare earth based Upconversion nanoparticles. Optical coherence tomography (OCT) has been used to explore the particles ability to increase contrast and improve signal intensity. Photo thermal OCT, a function extension of OCT has been used to gauge the photo thermal potential of the nanoparticles. The nanoparticles successfully improved contrast and information from the deeper layers of the sample. The particles also showed excellent capability for use as photo thermal agents.

Comparative studies of upconversion luminescence and optical temperature sensing in Tm3+/Yb3+ codoped LaVO4 and GdVO4 phosphors.

Tm3+/Yb3+ codoped LaVO4 and GdVO4 phosphors are successfully synthesized using solid state reaction methods and then upconversion emission studies are performed. X-ray diffraction has confirmed a pure monoclinic phase of LaVO4 and a tetragonal phase of GdVO4. Upconversion emission through 980 nm laser diode excitation has shown a strong blue band at 475 nm and two weak red bands at 647 and 700 nm originating from 1G4 → 3H6, 1G4 → 3F4 and 3F3 → 3H6 transitions of Tm3+ ions, respectively. Non-thermally coupled levels viz.3F3 (700 nm) and 1G4 (475 nm) in both the phosphors are used for fluorescence intensity ratio based optical thermometric studies and a comparison is made. The FIR data against temperature were fitted with polynomial and exponential fittings. The results show that polynomial fitting has a higher absolute sensitivity of 21.2 × 10-3 K-1 at 653 K for the LaVO4: Tm3+/Yb3+ phosphor than the exponential fitting sensitivity of 19.0 × 10-3 K-1 at 653 K, while in the case of the GdVO4: Tm3+/Yb3+ phosphor both fitting functions provided the same value of absolute sensitivity, that is 13.0 × 10-3 K-1 at 653 K. A comparison of the sensitivity values shows that the LaVO4: Tm3+/Yb3+ phosphor provides higher sensitivity than the GdVO4: Tm3+/Yb3+phosphor but the latter one is too high in upconversion emission.

Probing multimodal light emission from Tb3+/Yb3+-doped garnet nanophosphors for lighting applications.

Herein we report the solution-combustion-method-synthesized Tb3+- and Tb3+/Yb3+-doped Gd3Ga5O12 nanophosphors, which possess luminescent and magnetic properties. The phase formation/crystal structure, and morphology of the prepared nanophosphors are studied using X-ray diffraction (XRD)/Raman spectroscopy and a field emission scanning electron microscope (FE-SEM), respectively. Tb3+/Yb3+-doped phosphor samples exhibit green emission with an intense band around 544 nm through downshifting (DS) and upconversion (UC) processes because of the 5D4 → 7F5 transition of Tb3+. In addition to this visible emission, these samples also show a NIR emission band around 1024 nm via the quantum cutting (QC) process due to the 2F5/2 → 2F7/2 transition of Yb3+. Emission decay measurements of the 5D4 → 7F5 transition of Tb3+ are performed to obtain the rate of energy transfer from Tb3+ to nearby Yb3+. Furthermore, using this energy transfer, the quantum cutting efficiencies were estimated. For their practical application, a selected sample was used to fabricate a LED device by combining the sample with a UV-C LED (274 nm). The obtained results, such as the activation energy (∼0.20 eV) and the high CRI value (78), suggest that the prepared sample can be utilized as a green-light-emitting agent in phosphor-coated (pc) WLEDs.

Synthesis and upconversion emission studies of CaYF5:Ho3+/Yb3+ phosphor and its applications in optical thermometry, fingerprint detection, and security ink.

In this work, a CaYF5:Ho3+/Yb3+ upconversion phosphor was synthesized and its structural, morphological, and optical properties were studied. The upconversion emission study was performed at an excitation pump power density of 5 W cm-2 and emissions at 544 nm, 650 nm and 747 nm due to the 5F4(5S2) → 5I8, 5F5 → 5I8 and 5F4(5S2) → 5I7 transitions of the Ho3+ ion, respectively were observed. From temperature-dependent upconversion spectra temperature sensitivity was calculated and sensitivity is found to be 14 × 10-3 K-1 for the synthesized upconversion phosphor. The photothermal conversion efficiency of the prepared sample in ethanol medium was tested. Moreover, the sample was used to develop latent fingerprints on various surfaces and good contrast in recorded images is observed. The invisible ink was prepared using the upconversion phosphor and then written words were recorded in upconversion emission mode.