Near-infrared (808 and 980 nm) excited photoluminescence study in Nd-doped Y2O3phosphor for bio-imaging

Effect of the Growth Conditions on Organic Crystals with Rare Earth Ions and 1,10-Phenanthroline

Using a simple solution growth technique, we grow crystals with phenanthroline as a ligand and various rare earth ions: thulium (Tm), ytterbium (Yb), gadolinium (Gd), lanthanum (La), neodymium (Nd), europium (Eu), and erbium (Er). We then selected the composition that forms thin plates with well-defined shapes, Er(NO3)Phen2, and explored the effects of various conditions on crystal formation and growth, including temperature regime, light illumination, and substrates where the crystals are formed and grown. The composition and local environment strongly affect the size and shape of microcrystals and substrate coverage. The use of gold substrates significantly enhances the crystal growing process. Elevated temperatures negatively affect the crystal growth.

Transparent nanocrystal-in-glass composite fibers for multifunctional temperature and pressure sensing

The pursuit of compact and integrated devices has stimulated a growing demand for multifunctional sensors with rapid and accurate responses to various physical parameters, either separately or simultaneously. Fluorescent fiber sensors have the advantages of robust stability, light weight, and compact geometry, enabling real-time and noninvasive signal detection by monitoring the fluorescence parameters. Despite substantial progress in fluorescence sensors, achieving multifunctional sensing in a single optical fiber remains challenging. To solve this problem, in this study, we present a bottom-up strategy to design and fabricate thermally drawn multifunctional fiber sensors by incorporating functional nanocrystals with temperature and pressure fluorescence responses into a transparent glass matrix. To generate the desired nanocrystal-in-glass composite (NGC) fiber, the fluorescent activators, incorporated nanocrystals, glassy core materials, and cladding matrix are rationally designed. Utilizing the fluorescence intensity ratio technique, a self-calibrated fiber sensor is demonstrated, with a bi-functional response to temperature and pressure. For temperature sensing, the NGC fiber exhibits temperature-dependent near-infrared emission at temperatures up to 573 K with a maximum absolute sensitivity of 0.019 K-1. A pressure-dependent upconversion emission is also realized in the visible spectral region, with a linear slope of -0.065. The successful demonstration of multifunctional NGC fiber sensors provides an efficient pathway for new paradigms of multifunctional sensors as well as a versatile strategy for future hybrid fibers with novel combinations of magnetic, optical, and mechanical properties.

Comparative study of upconversion and photoacoustic measurements of Er3+/Yb3+ doped La2O3 phosphor under 980 nm

The Er3+/Yb3+doped La2O3 phosphor samples were synthesized by the combustion method and then photoluminescence and photoacoustic spectroscopic studies were done. Prepared samples were annealed at 800 °C, 1000 °C and 1300 °C and all samples were found in pure hexagonal phase as confirmed by XRD analysis. From FE-SEM images it is found that particle size increases with increase in annealing temperature. The frequency upconversion emission spectra of samples were recorded by exciting the sample with 980 nm diode laser and maximum emission intensity is obtained for the sample annealed at 1000 °C for 2 h. A photoacoustic cell was designed and wavelength dependent photoacoustic spectra were measured. The effect of sample storage time on radiative and non-radiative emission properties of sample was checked by measuring upconversion emission and photoacoustic spectra, simultaneously. It is observed that the emission intensity and photoacoustic signal both decreases with time. The maximum photoacoustic signal is obtained around 974 nm wavelength and it indicates its potential for photo-thermal therapy using infrared excitation.

Rare earth-doped nanocrystals for bioimaging in the near-infrared region

Rare earth-doped nanocrystals are widely used in medical diagnostics and bioimaging due to their narrow luminescence emission spectra (10-20 nm), long lifetime, and no photobleaching properties. Especially in the near-infrared (NIR) region, deeper tissue imaging can be achieved with low background luminescence and high spatial resolution. Further precise image-guided diagnosis and treatment can be achieved by using multimodal imaging such as MRI/CT/NIR/PA. Here, we focus on the construction of rare earth-doped nanocrystals, optical properties, and progress of such nanocomposites for bioimaging in the NIR region. In addition, the limitations at this stage in the field of bioimaging and the prospects for future technological development of rare earth-doped nanocrystals are present.

Boltzmann relation reliability in optical temperature sensing based on upconversion studies of Er3+ /Yb3+ codoped PZT ceramics

The fluorescence intensity ratio (FIR) of two thermally coupled levels with temperature follows the Boltzmann equation and shows an exponential nature to the temperature which is purely dependent on the energy difference between the levels. Despite the identical energy difference between the thermally coupled levels, researchers have observed varying sensitivities for various samples. In this article, the FIR and sensitivities were calculated using the Boltzmann equation by changing various parameters such as energy difference (ΔE) and the value of the constant C. The results were compared with various reports for Er³⁺ /Yb³⁺ ions. After analysis, a new polynomial fit equation was used to determine the temperature sensitivities for the Er³⁺ /Yb³⁺ codoped PbZrTiO₃ phosphor in lieu of the conventional Boltzmann equation. The polynomial fit equation eliminated the dependency of the sensitivity on the inverse of the FIR factor and a flat sensitivity curve was obtained with temperature.