Broadband Profiled Eye-Safe Emission of LMA Silica Fiber Doped with Tm3+/Ho3+ Ions

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.

Broadband 1.5-2.1 µm emission in gallo-germanate dual-core optical fiber co-doped with Er3+ and Yb3+/Tm3+/Ho3

The near-infrared emission in fabricated low-phonon energy, gallo-germanate glass, and double-core optical fiber has been investigated. Broadband amplified spontaneous emission (ASE) was obtained in optical fiber with cores doped with: 1st - 0.2Er2O3 and 2nd - 0.5Yb2O3/0.4Tm2O3/0.05Ho2O3 as a result of the superposition of emission bands from both cores corresponding to the Er3+:4I13/2→4I15/2 (1st core) and Tm3+:3F4 → 3H6/Ho3+:5I7 → 5I8 (2nd core) transitions. The effect of fiber length and pump wavelength on the near-infrared amplified spontaneous emission (ASE) properties has been analyzed for 1 m and 5 m optical fiber. The widest emission bandwidth (355 nm - 3 dB level) was obtained for a 5 m length optical fiber pumped by a 940 nm laser.

Tm3+/Ho3+ profiled co-doped core area optical fiber for emission in the range of 1.6-2.1 µm

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.

Investigation of Thermal Sensing in Fluoroindate Yb3+/Er3+ Co-Doped Optical Fiber

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-²H_11/2 and ⁴S_3/2), non-thermally coupled levels (non-TCLs-⁴F_7/2 and ⁴F_9/2), 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 ²H_11/2 → ⁴S_3/2 transition) and relative sensitivity (2.05% K^-1-glass, 1.64% K^-1-glass fiber ⁴F_7/2 → ⁴F_9/2 transition), as well as high repeatability of the signal, indicate that this material could be used in temperature sensing applications.

Analysis of Excitation Energy Transfer in LaPO4 Nanophosphors Co-Doped with Eu3+/Nd3+ and Eu3+/Nd3+/Yb3+ Ions

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 (⁴F_3/2 → ⁴I_9/2:Nd³⁺) were observed. At 980 nm, 991 nm, 1033 nm (²F_5/2 → ²F_7/2:Yb³⁺) and 1048 nm, 1060 nm, 1073 nm, and 1080 nm (⁴F_3/2 → ⁴I_9/2:Nd³⁺), strong bands of luminescence were visible in the 950 nm-1100 nm range, demonstrating that energy transfer took place.

The Effect of Fluorides (BaF2, MgF2, AlF3) on Structural and Luminescent Properties of Er3+-Doped Gallo-Germanate Glass

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.

Crystallization Mechanism and Optical Properties of Antimony-Germanate-Silicate Glass-Ceramic Doped with Europium Ions

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.

Fluoroindate glasses co-doped with Pr3+/Er3+ for near-infrared luminescence applications

Fluoroindate glasses co-doped with Pr³⁺/Er³⁺ ions were synthesized and their near-infrared luminescence properties have been examined under selective excitation wavelengths. For the Pr³⁺/Er³⁺ co-doped glass samples several radiative and nonradiative relaxation channels and their mechanisms are proposed under direct excitation of Pr³⁺ and/or Er³⁺. The energy transfer processes between Pr³⁺ and Er³⁺ ions in fluoroindate glasses were identified. In particular, broadband near-infrared luminescence (FWHM = 278 nm) associated to the ¹G₄ → ³H₅ (Pr³⁺), ¹D₂ → ¹G₄ (Pr³⁺) and ⁴I_13/2 → ⁴I_15/2 (Er³⁺) transitions of rare earth ions in fluoroindate glass is successfully observed under direct excitation at 483 nm. Near-infrared luminescence spectra and their decays for glass samples co-doped with Pr³⁺/Er³⁺ are compared to the experimental results obtained for fluoroindate glasses singly doped with rare earth ions.

Luminescent Studies on Germanate Glasses Doped with Europium Ions for Photonic Applications

Glass and ceramic materials doped with rare earth (RE) ions have gained wide interest in photonics as active materials for lasers, optical amplifiers, and luminescent sensors. The emission properties of RE-doped glasses depend on their chemical composition, but they can also be tailored by modifying the surrounding active ions. Typically, this is achieved through heat treatment (including continuous-wave and pulsed lasers) after establishing the ordering mechanisms in the particular glass-RE system. Within the known systems, silicate glasses predominate, while much less work relates to materials with lower energy phonons, which allow more efficient radiation sources to be constructed for photonic applications. In the present work, the luminescent and structural properties of germanate glasses modified with phosphate oxide doped with Eu3+ ions were investigated. Europium dopant was used as a "spectroscopic probe" in order to analyze the luminescence spectra, which characterizes the changes in the local site symmetries of Eu3+ ions. Based on the spectroscopic results, a strong influence of P2O5 content was observed on the excitation and luminescence spectra. The luminescence study of the most intense 5D0→7F2 (electric dipole) transition revealed that the increase in the P2O5 content leads to the linewidth reduction (from 15 nm to 10 nm) and the blue shift (~2 nm) of the emission peak. According to the crystal field theory, the introduction of P2O5 into the glass structure changes the splitting number of sublevels of the 5D0→7F1 (magnetic dipole) transition, confirming the higher polymerization of fabricated glass. The slightly different local environment of Eu3+ centers the results in a number of sites and causes inhomogeneous broadening of spectral lines. It was found that the local asymmetry ratio estimated by the relation of (5D0→7F2)/(5D0→7F1) transitions also confirms greater changes in local symmetry around Eu3+ ions. Our results indicate that modification of germanate glass by P2O5 allows control of their structural properties in order to functionalize the emissions for application as luminescent light sources and sensors.

Synthesis and characterization of poly(methyl methacrylate) co-doped with Tb(tmhd)3 - Rhodamine B for luminescent optical fiber applications

Currently, there is a growing interest in the development of multi-colored materials based on the combination of two or more systems (organic or inorganic) as a strategy to take advantage of their combined physical or chemical properties. These multi-colored materials have found potential applications as sensors, amplifiers, and optical fibers. In this work, the physical characteristics of poly(methyl methacrylate) (PMMA) doped with Terbium(III)-tris-(2,2,6,6-tetramethyl-3,5-heptanedionate) (Tb(tmhd)₃) at 1.57-1.58 mmol and Rhodamine B (RhB) at different concentrations were analyzed. The emission obtained from these samples (multichromophoric samples) varied as function of RhB concentration due to an efficient energy transfer process (33-65%). The role of PMMA as inert matrix that assists in the recombination process was confirmed by FTIR and Raman spectra analysis. Moreover, an improvement in thermal resistance of the materials was observed due to the presence of the dopants during the polymerization process.