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LMA (Large Mode Area) optical fibers are presently under active investigation to explore their potential for generating laser action or broadband emission directly within the optical fiber structure. Additionally, a wide mode profile significantly reduces the power distribution density in the fiber cross-section, minimizing the power density, photodegradation, or thermal damage. Multi-stage deposition in the MCVD-CDT system was used to obtain the structural doping profile of the LMA fiber multi-ring core doped with Tm3+ and Tm3+/Ho3+ layer profiles. The low alumina content (Al2O3: 0.03wt%) results in low refractive index modification. The maximum concentrations of the lanthanide oxides were Tm2O3: 0.18wt % and Ho2O3: 0.15wt%. The double-clad construction of optical fiber with emission spectra in the eye-safe spectral range of (1.55–2.10 µm). The calculated LP01 Mode Field Diameter (MFD) was 69.7 µm (@ 2000 nm, and 1/e of maximum intensity), which confirms LMA fundamental mode guiding conditions. The FWHM and λmax vs. fiber length are presented and analyzed as a luminescence profile modification. The proposed structured optical fiber with a ring core can be used in new broadband optical radiation source designs. [ABSTRACT FROM AUTHOR]

Double-clad optical fiber with a multi-ring core profile doped with thulium and holmium fabricated by Modified Chemical Vapor Deposition Chelate Doping Technology (MCVD-CDT) is presented. The measured Tm2O3 and Ho2O3 complexes' weight concentrations were 0.5% and 0.2% respectively. Numerical analyses show weakly guiding conditions and 42.2 µm of MFD LP01 at 2000 nm. The low NA numerical aperture (NA = 0.054) was obtained for the 20/250 µm core/cladding ratio optical fiber construction. The emission spectra in the range of 1.6–2.1 µm vs. the fiber length are presented. The full width at half maximum (FWHM) decreases from 318 to 270 nm for fiber lengths from 2 to 10 m. The presented fiber design is of interest for the development of new construction of optical fibers operating in the eye-safe spectral range. [ABSTRACT FROM AUTHOR]

An investigation of fluoroindate glass and fiber co-doped with Yb3+/Er3+ ions as a potential temperature sensor was assessed using the fluorescence intensity ratio (FIR) technique. Analysis of thermally coupled levels (TCLs—2H11/2 and 4S3/2), non-thermally coupled levels (non-TCLs—4F7/2 and 4F9/2), and their combination were examined. Additionally, the luminescent stability of the samples under constant NIR excitation using different density power at three different temperatures was carried out. The obtained values of absolute sensitivity (0.003 K−1—glass, 0.0019 K−1—glass fiber 2H11/2 → 4S3/2 transition) and relative sensitivity (2.05% K−1—glass, 1.64% K−1—glass fiber 4F7/2 → 4F9/2 transition), as well as high repeatability of the signal, indicate that this material could be used in temperature sensing applications. [ABSTRACT FROM AUTHOR]

Nanophosphors are widely used, especially in biological applications in the first and second biological windows. Currently, nanophosphors doped with lanthanide ions (Ln3+) are attracting much attention. However, doping the matrix with lanthanide ions is associated with a narrow luminescence bandwidth. This paper describes the structural and luminescence properties of co-doped LaPO4 nanophosphors, fabricated by the co-precipitation method. X-ray structural analysis, scanning electron microscope measurements with EDS analysis, and luminescence measurements (excitation 395 nm) of LaPO4:Eu3+/Nd3+ and LaPO4:Eu3+/Nd3+/Yb3+ nanophosphors were made and energy transfer between rare-earth ions was investigated. Tests performed confirmed the crystal structure of the produced phosphors and deposition of rare-earth ions in the structure of LaPO4 nanocrystals. In the range of the first biological window (650–950 nm), strong luminescence bands at the wavelengths of 687 nm and 698 nm (5D0 → 7F4:Eu3+) and 867 nm, 873 nm, 889 nm, 896 nm, and 907 nm (4F3/2 → 4I9/2:Nd3+) were observed. At 980 nm, 991 nm, 1033 nm (2F5/2 → 2F7/2:Yb3+) and 1048 nm, 1060 nm, 1073 nm, and 1080 nm (4F3/2 → 4I9/2:Nd3+), strong bands of luminescence were visible in the 950 nm–1100 nm range, demonstrating that energy transfer took place. [ABSTRACT FROM AUTHOR]

The effect of BaF2, MgF2, and AlF3 on the structural and luminescent properties of gallo-germanate glass (BGG) doped with erbium ions was investigated. A detailed analysis of infrared and Raman spectra shows that the local environment of erbium ions in the glass was influenced mainly by [GeO]4 and [GeO]6 units. Moreover, the highest number of non-bridging oxygens was found in the network of the BGG glass modified by MgF2. The 27Al MAS NMR spectrum of BGG glass with AlF3 suggests the presence of aluminum in tetra-, penta-, and octahedral coordination geometry. Therefore, the probability of the 4I13/2→4I15/2 transition of Er3+ ions increases in the BGG + MgF2 glass system. On the other hand, the luminescence spectra showed that the fluoride modifiers lead to an enhancement in the emission of each analyzed transition when different excitation sources are employed (808 nm and 980 nm). The analysis of energy transfer mechanisms shows that the fluoride compounds promote the emission intensity in different channels. These results represent a strong base for designing glasses with unique luminescent properties. [ABSTRACT FROM AUTHOR]

Glass-ceramic is semi-novel material with many applications, but it is still problematic in obtaining fibers. This paper aims to develop a new glass-ceramic material that is a compromise between crystallization, thermal stability, and optical properties required for optical fiber technology. This compromise is made possible by an alternative method with a controlled crystallization process and a suitable choice of the chemical composition of the core material. In this way, the annealing process is eliminated, and the core material adopts a glass-ceramic character with high transparency directly in the drawing process. In the experiment, low phonon antimony-germanate-silicate glass (SGS) doped with Eu3+ ions and different concentrations of P2O5 were fabricated. The glass material crystallized during the cooling process under conditions similar to the drawing processes'. Thermal stability (DSC), X-ray photo analysis (XRD), and spectroscopic were measured. Eu3+ ions were used as spectral probes to determine the effect of P2O5 on the asymmetry ratio for the selected transitions (5D0 → 7F1 and 5D0 → 7F2). From the measurements, it was observed that the material produced exhibited amorphous or glass-ceramic properties, strongly dependent on the nucleator concentration. In addition, the conducted study confirmed that europium ions co-form the EuPO4 structure during the cooling process from 730 °C to room temperature. Moreover, the asymmetry ratio was changed from over 4 to under 1. The result obtained confirms that the developed material has properties typical of transparent glass-ceramic while maintaining high thermal stability, which will enable the fabrication of fibers with the glass-ceramic core. [ABSTRACT FROM AUTHOR]