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.

Synthesis and photoluminescent characterization of ceramic phosphors Li2MgGeO4:Ln3+ (Ln3+ = Pr3+ or Tm3+) under different excitation wavelengths

In the current work, germanate phosphors Li₂MgGeO₄:Ln³⁺ (Ln = Pr, Tm) have been synthesized and then investigated using luminescence spectroscopy. The X-ray diffraction analysis demonstrate that ceramic compounds Li₂MgGeO₄ containing Pr³⁺ and Tm³⁺ ions crystallize in a monoclinic crystal lattice. Luminescence properties of Pr³⁺ and Tm³⁺ ions have been examined under different excitation wavelengths. The most intense blue emission band related to the ¹D₂ → ³F₄ transition of Tm³⁺ is overlaps well with broad band located near 500 nm, which is assigned to F-type centers. These effects are not evident for Pr³⁺ ions. Ceramic phosphors Li₂MgGeO₄:Ln³⁺ (Ln = Pr, Tm) are characterized based on measurements of the excitation/emission spectra and their decays. The experimental results indicate that germanate ceramics Li₂MgGeO₄ doped with trivalent rare earth ions can be applied as inorganic phosphors emitting orange (Pr³⁺) or blue (Tm³⁺) light.

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.

Raman and Infrared Spectroscopy of Barium-Gallo Germanate Glasses Containing B2O3/TiO2

Modified barium gallo-germanate glass hosts are still worthy of attention in studying structure-property relationships. In this work, two different series of glass systems based on (60-x)GeO₂-xTiO₂-30BaO-10Ga₂O₃ and (60-x)GeO₂-xB₂O₃-30BaO-10Ga₂O₃ (x = 10, 30, 50 mol%) were synthesized, and their properties were studied using spectroscopic techniques. X-ray diffraction (XRD) patterns revealed that all fabricated glasses were fully amorphous material. The absorption edge shifted toward the longer wavelengths with a gradual substitution of GeO₂. The spectroscopic assignments of titanium ions were performed with excitation and emission spectra compared to the additional sample containing an extremely low content of TiO₂ (0.005 mol%). On the basis of Raman and FT-IR investigations, it was found that increasing the TiO₂ content caused a destructive effect on the GeO₄ and GeO₆ structural units. The Raman spectra of a sample containing a predominantly TiO₂ (50 mol%) proved that the band was located near 650 cm^-1, which corresponded to the stretching vibration of Ti-O in TiO₆ unit. The deconvoluted IR results showed that the germanate glass network consisted of the coexistence of two BO₃ and BO₄ structural groups. Based on the experimental investigations, we concluded that the developed materials are a promising candidate for use as novel glass host matrices for doping rare-earth and/or transition metal ions.

Spectroscopic Properties of Pr3+, Tm3+, and Ho3+ in Germanate-Based Glass Systems Modified by TiO2

In this paper, the effect of the GeO₂:TiO₂ molar ratio in glass composition on the spectroscopic properties of germanate glasses was systematically investigated. The visible luminescence bands associated with characteristic ¹D₂ → ³H₄ (red), ⁵S₂, ⁵F₄ → ⁵I₈ (green), and ¹D₂ → ³F₄ (blue) transitions of Pr³⁺, Ho³⁺, and Tm³⁺ ions in systems modified by TiO₂ were well observed, respectively. It was found that the luminescence intensity of glasses containing Pr³⁺ and Ho³⁺ ions increases, whereas, for Tm³⁺-doped systems, luminescence quenching with increasing content of TiO₂ was observed. Based on Commission Internationale de I'Eclairage (CIE) chromaticity coordinates (x, y) analysis, it was demonstrated that the value of chromaticity coordinates for all glasses depends on the GeO₂:TiO₂ molar ratio. The addition of TiO₂ to system compositions doped with Tm³⁺ ions shifts the (x, y) to the center of the CIE diagram. However, chromaticity coordinates evaluated for glasses containing Pr³⁺ ions move to a purer red color. Our results confirm that the spectroscopic properties of the studied glasses strongly depend on TiO₂ content. Moreover, it can be stated that germanate-based glass systems modified by TiO₂ can be used for optoelectronics in RGB technology as red (Pr³⁺), green (Ho³⁺), and blue (Tm³⁺) emitters.

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.

Near-IR Luminescence of Rare-Earth Ions (Er3+, Pr3+, Ho3+, Tm3+) in Titanate-Germanate Glasses under Excitation of Yb3

Inorganic glasses co-doped with rare-earth ions have a key potential application value in the field of optical communications. In this paper, we have fabricated and then characterized multicomponent TiO₂-modified germanate glasses co-doped with Yb³⁺/Ln³⁺ (Ln = Pr, Er, Tm, Ho) with excellent spectroscopic properties. Glass systems were directly excited at 980 nm (the ²F_7/2 → ²F_5/2 transition of Yb³⁺). We demonstrated that the introduction of TiO₂ is a promising option to significantly enhance the main near-infrared luminescence bands located at the optical telecommunication window at 1.3 μm (Pr³⁺: ¹G₄ → ³H₅), 1.5 μm (Er³⁺: ⁴I_13/2 → ⁴I_15/2), 1.8 μm (Tm³⁺: ³F₄ → ³H₆) and 2.0 μm (Ho³⁺: ⁵I₇ → ⁷I₈). Based on the lifetime values, the energy transfer efficiencies (η_ET) were estimated. The values of η_ET are changed from 31% for Yb³⁺/Ho³⁺ glass to nearly 53% for Yb³⁺/Pr³⁺ glass. The investigations show that obtained titanate-germanate glass is an interesting type of special glasses integrating luminescence properties and spectroscopic parameters, which may be a promising candidate for application in laser sources emitting radiation and broadband tunable amplifiers operating in the near-infrared range.

Influence of glass formers and glass modifiers on spectral properties and CIE coordinates of Dy3+ ions in lead-free borate glasses

Spectral properties of lead-free glasses doped with Dy³⁺ ions in function of glass formers and glass modifiers were studied. The glass systems in a function of concentration GeO₂ and CaO/SrO/BaO which was partially or totally replaced by CaF₂/SrF₂/BaF₂ were synthesized. The visible luminescence spectra for obtained glasses were registered and value of parameters such as ratio of yellow-to-blue luminescence and the Commission Internationale de I'Eclairage (CIE) chromaticity coordinates (x, y) were analyzed in detail. The Y/B increase from 2.97 to 3.8 in systems with increasing of concentration glass former (GeO₂), whereas ratio Y/B slightly decreases when the of content fluoride glass modifiers increases. The obtained results confirm that impact on visible luminescence of lead-free borate glasses doped with Dy³⁺ ions is greater for glass former than glass modifier. Moreover, studied systems can be used for optoelectronic as yellowish emitters.

Spectroscopic Properties of Inorganic Glasses Doped with Pr3+: A Comparative Study

The results presented in this communication concern visible and near-IR emission of Pr3+ ions in selected inorganic glasses, i.e., borate-based glass with Ga2O3 and BaO, lead-phosphate glass with Ga2O3, gallo-germanate glass modified by BaO/BaF2, and multicomponent fluoride glass based on InF3. Glasses present several emission bands at blue, reddish orange, and near-infrared spectral ranges, which correspond to 4f–4f electronic transitions of Pr3+. The profiles of emission bands and their relative intensity ratios depend strongly on glass-host. Visible emission of Pr3+ ions is tuned from red/orange for borate-based glass to nearly white light for multicomponent fluoride glass based on InF3. The positions and spectral linewidths for near-infrared luminescence bands at the optical telecommunication window corresponding to the 1G4 → 3H5, 1D2 → 1G4, and 3H4 → 3F3,3F4 transitions of Pr3+ are dependent on glass-host matrices and excitation wavelengths. Low-phonon fluoride glasses based on InF3 and gallo-germanate glasses with BaO/BaF2 are excellent candidates for broadband near-infrared optical amplifiers. Spectroscopic properties of Pr3+-doped glasses are compared and discussed in relation to potential optical applications.

Investigation of the TeO2/GeO2 Ratio on the Spectroscopic Properties of Eu3+-Doped Oxide Glasses for Optical Fiber Application

This study presented an analysis of the TeO2/GeO2 molar ratio in an oxide glass system. A family of melt-quenched glasses with the range of 0-35 mol% of GeO2 has been characterized by using DSC, Raman, MIR, refractive index, PLE, PL spectra, and time-resolved spectral measurements. The increase in the content of germanium oxide caused an increase in the transition temperature but a decrease in the refractive index. The photoluminescence spectra of europium ions were examined under the excitation of 465 nm, corresponding to 7F0 → 5D2 transition. The PSB (phonon sidebands) analysis was carried out to determine the phonon energy of the glass hosts. It was reported that the red (5D0 → 7F2) to orange (5D0 → 7F1) fluorescence intensity ratio for Eu3+ ions decreased from 4.49 (Te0Ge) to 3.33 (Te15Ge) and showed a constant increase from 4.58 (Te20Ge) to 4.88 (Te35Ge). These optical features were explained in structural studies, especially changes in the coordination of [4]Ge to [6]Ge. The most extended lifetime was reported for the Eu3+ doped glass with the highest content of GeO2. This glass was successfully used for the drawing of optical fiber.

Structure and Luminescence Properties of Transparent Germanate Glass-Ceramics Co-Doped with Ni2+/Er3+ for Near-Infrared Optical Fiber Application

An investigation of the structural and luminescent properties of the transparent germanate glass-ceramics co-doped with Ni²⁺/Er³⁺ for near-infrared optical fiber applications was presented. Modification of germanate glasses with 10–20 ZnO (mol.%) was focused to propose the additional heat treatment process controlled at 650 °C to obtain transparent glass-ceramics. The formation of 11 nm ZnGa₂O₄ nanocrystals was confirmed by the X-ray diffraction (XRD) method. It followed the glass network changes analyzed in detail (MIR—Mid Infrared spectroscopy) with an increasing heating time of precursor glass. The broadband 1000–1650 nm luminescence (λ_exc = 808 nm) was obtained as a result of Ni²⁺: ³T₂(³F) → ³A₂(³F) octahedral Ni²⁺ ions and Er³⁺: ⁴I_13/2 → ⁴I_15/2 radiative transitions and energy transfer from Ni²⁺ to Er³⁺ with the efficiency of 19%. Elaborated glass–nanocrystalline material is a very promising candidate for use as a core of broadband luminescence optical fibers.

Broadband Near-Infrared Luminescence in Lead Germanate Glass Triply Doped with Yb3+/Er3+/Tm3

This paper deals with broadband near-infrared luminescence properties of lead germanate glass triply doped with Yb³⁺/Er³⁺/Tm³⁺. Samples were excited at 800 nm and 975 nm. Their emission intensities and lifetimes depend significantly on Er³⁺ and Tm³⁺ concentrations. For samples excited at 800 nm, broadband emissions corresponding to the overlapped ³H₄ → ³F₄ (Tm³⁺) and ⁴I_13/2 → ⁴I_15/2 (Er³⁺) transitions centered at 1.45 µm and 1.5 µm was identified. Measurements of decay curves confirm reduction of ³H₄ (Tm³⁺), ²F_5/2 (Yb³⁺) and ⁴I_13/2 (Er³⁺) luminescence lifetimes and the presence of energy-transfer processes. The maximal spectral bandwidth equal to 269 nm for the ³F₄ → ³H₆ transition of Tm³⁺ suggests that our glass co-doped with Yb³⁺/Er³⁺/Tm³⁺ is a good candidate for broadband near-infrared emission. The energy transfer from ⁴I_13/2 (Er³⁺) to ³F₄ (Tm³⁺) and cross-relaxation processes are responsible for the enhancement of broadband luminescence near 1.8 µm attributed to the ³F₄ → ³H₆ transition of thulium ions in lead germanate glass under excitation of Yb³⁺ ions at 975 nm.

Structural and Photoluminescence Investigations of Tb3+/Eu3+ Co-Doped Silicate Sol-Gel Glass-Ceramics Containing CaF2 Nanocrystals

In this work, the series of Tb3+/Eu3+ co-doped xerogels and derivative glass-ceramics containing CaF2 nanocrystals were prepared and characterized. The in situ formation of fluoride crystals was verified by an X-ray diffraction technique (XRD) and transmission electron microscopy (TEM). The studies of the Tb3+/Eu3+ energy transfer (ET) process were performed based on excitation and emission spectra along with luminescence decay analysis. According to emission spectra recorded under near-ultraviolet (NUV) excitation (351 nm, 7F6 → 5L9 transition of Tb3+), the mutual coexistence of the 5D4 → 7FJ (J = 6-3) (Tb3+) and the 5D0 → 7FJ (J = 0-4) (Eu3+) luminescence bands was clearly observed. The co-doping also resulted in gradual shortening of a lifetime from the 5D4 state of Tb3+ ions, and the ET efficiencies were varied from ηET = 11.9% (Tb3+:Eu3+ = 1:0.5) to ηET = 22.9% (Tb3+:Eu3+ = 1:2) for xerogels, and from ηET = 25.7% (Tb3+:Eu3+ = 1:0.5) up to ηET = 67.4% (Tb3+:Eu3+ = 1:2) for glass-ceramics. Performed decay analysis from the 5D0 (Eu3+) and the 5D4 (Tb3+) state revealed a correlation with the change in Tb3+-Eu3+ and Eu3+-Eu3+ interionic distances resulting from both the variable Tb3+:Eu3+ molar ratio and their partial segregation in CaF2 nanophase.

Phonon Sideband Analysis and Near-Infrared Emission in Heavy Metal Oxide Glasses

In this work, spectroscopic properties of europium and erbium ions in heavy metal oxide glasses have been studied. The phonon energy of the glass host was determined based on Eu³⁺ excitation spectra measurements. Near-IR emission spectra at 1550 nm related to ⁴I_13/2 → ⁴I_15/2 transition of erbium in heavy metal glasses were examined with special regards to luminescence bandwidth and measured lifetime. In particular, correlation between phonon energy and the measured lifetime ⁴I_13/2 (Er³⁺) was proposed. The luminescence lifetime for the ⁴I_13/2 upper laser state of erbium decreases with increasing phonon energy in glass matrices. Completely different results were obtained glass samples with europium ions, where the ⁵D₀ lifetime increases with increasing phonon energy. Our investigations suggest that the values of measured ⁵D₀ lifetime equal to radiative lifetimes for all heavy metal oxide glasses.

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.

Lead Borate Glasses and Glass-Ceramics Singly Doped with Dy3+ for White LEDs

In this paper, some series of lead borate glasses and glass ceramics singly doped with Dy³⁺ ions were prepared and then studied using spectroscopic techniques. Our research includes mainly studies of the luminescence properties of received materials for white light. The luminescence bands associated with the characteristic ⁴F_9/2→⁶H_15/2 (blue), ⁴F_9/2→⁶H_13/2 (yellow) and ⁴F_9/2→⁶H_11/2 (red) transitions of trivalent dysprosium in lead borate systems are well observed. In particular, the Commission Internationale de I’Eclairage (CIE) chromaticity coordinates (x, y) were calculated in relation to potential applications for white light-emitting diodes (W-LEDs). Their values depend on the relative B₂O₃/PbO ratios and PbX₂ contents (where X = Cl, F, Br) in glass composition. For glass-ceramics, the chromaticity coordinates are changed significantly under different excitation wavelengths.

Influence of Oxide Glass Modifiers on the Structural and Spectroscopic Properties of Phosphate Glasses for Visible and Near-Infrared Photonic Applications

The effect of oxide modifiers on multiple properties (structural and spectroscopic) of phosphate glasses with molar composition 60P₂O₅-(10-x)Ga₂O₃-30MO-xEu₂O₃ and 60P₂O₅-(10-y)Ga₂O₃-30MO-yEr₂O₃ (where M = Ca, Sr, Ba; x = 0, 0.5; y = 0, 1) were systematically examined and discussed. The local structure of systems was evidenced by the infrared (IR-ATR) and Raman spectroscopic techniques. The spectroscopic behaviors of the studied glass systems were determined based on analysis of recorded spectra (excitation and emission) as well as luminescence decay curves. Intense red and near-infrared emissions (1.5 μm) were observed for samples doped with Eu³⁺ and Er³⁺ ions, respectively. It was found that the value of fluorescence intensity ratio R/O related to ⁵D₀→⁷F₂ (red) and ⁵D₀→⁷F₁ (orange) transition of Eu³⁺ ions depends on the oxide modifiers MO in the glass host. However, no clear influence of glass modifiers on the luminescence linewidth (FWHM) was observed for phosphate systems doped with Er³⁺ ions. Moreover, the ⁵D₀ and ⁴I_13/2 luminescence lifetimes of Eu³⁺ and Er³⁺ ions increase with the increasing ionic radius of M²⁺ (M = Ca, Sr, Ba) in the host matrix. The obtained results suggest the applicability of the phosphate glasses with oxide modifiers as potential red and near-infrared photoluminescent materials in photonic devices.

Novel Multicomponent Titanate-Germanate Glasses: Synthesis, Structure, Properties, Transition Metal, and Rare Earth Doping

Novel multicomponent titanate-germanate glasses singly doped with transition metal (Cr³⁺) and rare earth ions (Eu³⁺) were synthesized and the glass transition temperatures and thermal stability parameters were determined using DSC measurements. X-ray diffraction analysis confirmed fully amorphous nature of the received samples. Their structural and optical properties were compared with germanate glasses without TiO₂. Correlation between local structure and optical properties in titanate-germanate glasses is well evidenced by FT-IR, Raman, EPR, and luminescence spectroscopy. In particular, luminescence spectra and their decays are examined for glass samples, where GeO₂ was partially substituted by TiO₂.

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.

Reddish-Orange Luminescence from BaF2:Eu3+ Fluoride Nanocrystals Dispersed in Sol-Gel Materials

Nanocrystalline transparent BaF2:Eu3+ glass-ceramic materials emitting reddish-orange light were fabricated using a low-temperature sol-gel method. Several experimental techniques were used to verify structural transformation from precursor xerogels to sol-gel glass-ceramic materials containing fluoride nanocrystals. Thermal degradation of xerogels was analyzed by thermogravimetric analysis (TG) and differential scanning calorimetry method (DSC). The presence of BaF2 nanocrystals dispersed in sol-gel materials was confirmed by the X-ray diffraction (XRD) analysis and transmission electron microscopy (TEM). In order to detect structural changes in silica network during annealing process, the infrared spectroscopy (IR-ATR) was carried out. In particular, luminescence spectra of Eu3+ and their decays were examined in detail. Some spectroscopic parameters of Eu3+ ions in glass-ceramics containing BaF2 nanocrystals were determined and compared to the values obtained for precursor xerogels. It was observed, that the intensities of two main red and orange emission bands corresponding to the 5D0→7F2 electric-dipole transition (ED) and the 5D0→7F1 magnetic-dipole (MD) transition are changed significantly during transformation from xerogels to nanocrystalline BaF2:Eu3+ glass-ceramic materials. The luminescence decay analysis clearly indicates that the measured lifetime 5D0 (Eu3+) considerably enhanced in nanocrystalline BaF2:Eu3+ glass-ceramic materials compared to precursor xerogels. The evident changes in luminescence spectra and their decays suggest the successful migration of Eu3+ ions from amorphous silica network to low-phonon BaF2 nanocrystals.

Spectroscopic Properties of Erbium-Doped Oxyfluoride Phospho-Tellurite Glass and Transparent Glass-Ceramic Containing BaF2 Nanocrystals

The ErF₃-doped oxyfluoride phospho-tellurite glasses in the (40-x) TeO₂-10P₂O₅-45 (BaF₂-ZnF₂) -5Na₂O-xErF₃ system (where x = 0.25, 0.50, 0.75, 1.00, and 1.25 mol%) have been prepared by the conventional melt-quenching method. The effect of erbium trifluoride addition on thermal, structure, and spectroscopic properties of oxyfluoride phospho-tellurite precursor glass was studied by differential scanning calorimetry (DSC), Fourier-transform infrared (FTIR), and Raman spectroscopy as well as emission measurements, respectively. The DSC curves were used to investigate characteristic temperatures and thermal stability of the precursor glass doped with varying content of ErF₃. FTIR and Raman spectra were introduced to characterize the evolution of structure and phonon energy of the glasses. It was found that the addition of ErF₃ up to 1.25 mol% into the chemical composition of phospho-tellurite precursor glass enhanced 2.7 µm emission and upconversion. By controlled heat-treatment process of the host glass doped with the highest content of erbium trifluoride (1.25 mol%), transparent erbium-doped phospho-tellurite glass-ceramic (GC) was obtained. X-ray diffraction analysis confirmed the presence of BaF₂ nanocrystals with the average 16 nm diameter in a glass matrix. Moreover, MIR, NIR, and UC emissions of the glass-ceramic were discussed in detail and compared to the spectroscopic properties of the glass doped with 1.25 mol% of ErF₃ (the base glass).

Investigation of the aluminum oxide content on structural and optical properties of germanium glasses doped with RE ions

In this paper structural and optical properties of Rare Earth doped (RE) gallo-germanate glasses modified with various amount of Al₂O₃ have been investigated. Glasses doped with Yb³⁺, Tm^3+, and Ho³⁺ ions were synthesized to study Al₂O₃ additive influence on their structural and emission properties in the visible spectral region. MIR spectra indicated that the structure of prepared glasses tends to order and its polymerization along with the aluminum content increase. Glass samples consisting of the low molar content of Al₂O₃ are characterized by a significant contribution of Tm³⁺ ions in light emission while Ho³⁺ ions luminescence dominates in samples consisting of the higher molar content of Al₂O₃. Additionally, investigation of light emission in visible range showed that samples consisting of the low molar content of Al₂O₃ are characterized by greenish blue light emission whereas light emitted by samples consisting of 15-20 mol% is much closer to the white colour.

Rare earth-doped barium gallo-germanate glasses and their near-infrared luminescence properties

Near-infrared luminescence properties of Nd³⁺ and Ho³⁺ ions in barium gallo-germanate glasses have been reported. Several spectroscopic parameters for Nd³⁺ and Ho³⁺ ions have been determined from the Judd-Ofelt analysis and absorption/luminescence measurements. Quite large luminescence lifetime, quantum efficiency and stimulated emission cross-section have been obtained for the main ⁴F_3/2 → ⁴I_11/2 (Nd³⁺) and ⁵I₇ → ⁵I₈ (Ho³⁺) laser transitions of rare earths in barium gallo-germanate glasses. It suggests that barium gallo-germanate glass is promising for near-infrared laser application at emission wavelengths 1064 nm (Nd³⁺) and 2020 nm (Ho³⁺).

Structural and optical properties of antimony-germanate-borate glass and glass fiber co-doped Eu3+ and Ag nanoparticles

In the paper analysis of structural and luminescent properties of antimony-germanate-borate glasses and glass fiber co-doped with 0.6AgNO₃/0.2Eu₂O₃are presented. Heat treatment of the fabricated glass and optical fiber (400 °C, 12 h) enabled to obtain Ag nanoparticles (NPs) with average size 30-50 nm on their surface. It has been proofed that silver ions migrate to the glass surface, where they are reduced to Ag⁰ nanoparticles. Simultaneously, FTIR analysis showed that heat treatment of the glass and optical fiber increases the local symmetry of the Eu³⁺ site.

Spectroscopy and energy transfer in lead borate glasses doubly doped with Tm3+ and Dy3+ ions

Lead borate glasses singly and doubly doped with Tm³⁺ and Dy³⁺ were prepared by traditional melt-quenching technique. The emission spectra of rare earths in studied glass systems were registered under different excitation wavelengths. The observed emission bands are located in the visible spectral region. They correspond to ¹D₂→³F₄ (blue) and ¹G₄→³H₆ (blue) transitions of Tm³⁺ as well as ⁴F_9/2→⁶H_15/2 (blue), ⁴F_9/2→⁶H_13/2 (yellow) and ⁴F_9/2→⁶H_11/2 (red) transitions of Dy³⁺. Moreover, the energy transfer process from Tm³⁺ to Dy³⁺ was observed. The luminescence bands originating to characteristic transitions of thulium and dysprosium ions are present on emission spectra under direct excitation of Tm³⁺. Luminescence lifetimes for the excited states of Tm³⁺ and Dy³⁺ ions in lead borate glass were also determined based on decay measurements. The luminescence intensities and lifetimes depend significantly on the relative concentrations of the optically active dopants.

Optical Characterization of Nano- and Microcrystals of EuPO₄ Created by One-Step Synthesis of Antimony-Germanate-Silicate Glass Modified by P₂O₅

Technology of active glass-ceramics (GC) is an important part of luminescent materials engineering. The classic method to obtain GC is based on annealing of parent glass in proper temperature and different time periods. Generally, only the bulk materials are investigated as a starting host for further applications. However, the effect of an additional heat-treatment process on emission and structural properties during GC processing is omitted. Here, we focus on the possibility of obtaining transparent glass-ceramic doped with europium ions directly with a melt-quenching method. The influence of phosphate concentration (up to 10 mol %) on the inversion symmetry of local environment of Eu3+ ions in antimony-germanate-silicate (SGS) glass has been investigated. The Stark splitting of luminescence spectra and the local asymmetry ratio estimated by relation of (⁵D₀→⁷F₂)/(⁵D₀→⁷F₁) transitions in fabricated glass confirms higher local symmetry around Eu3+ ions. Based on XRD and SEM/EDX measurements, the EuPO₄ nano- and microcrystals with monoclinic geometry were determined. Therefore, in our experiment, we confirmed possibility of one-step approach to fabricate crystalline structures (glass-ceramic) in Eu-doped SGS glass without additional annealing process.

Analysis of upconversion luminescence in germanate glass and optical fiber codoped with Yb3+/Tb3+

In this paper, upconversion (UC) luminescence processes in a GeO₂-Ga₂O₃-BaO glass system codoped with 0.7Yb₂O₃/(0.07-0.7)Tb₂O₃ (mol.%) and double-clad optical fiber codoped with 0.7Yb₂O₃/0.7Tb₂O₃ (mol.%) were investigated. The highest emission intensity (energy transfer efficiency equals 12.92%) was obtained for 0.7Yb₂O₃/0.7Tb₂O₃ codoped glass. Comparative analysis showed significant differences in the shape of luminescence of fabricated germanate glass and optical fiber. Due to dominant transition from D₄5 sublevel the main green UC peak (Tb³⁺:  D₄5→F₅7) of fabricated double-clad optical fiber is shifted by 4 nm toward longer wavelengths.

Influence of BaF2 and activator concentration on broadband near-infrared luminescence of Pr3+ ions in gallo-germanate glasses

Thermal stability and broadband NIR luminescence of Pr(3+) doped gallo-germanate glasses with BaF2 have been studied. The thermal factors are larger for glass samples with low BaF2 content exhibiting good thermal stability against devitrification. Luminescence due to (1)D2 → (1)G4 transition of Pr(3+) was measured under 450 nm excitation. The (1)D2 measured lifetimes depend critically on activator concentration, but remain nearly unchanged with BaF2 content. The emission linewidth, the emission cross-section, the figure of merit (FOM) and the σem x FWHM product are relatively large, suggesting that Pr(3+)-doped gallo-germanate glasses with presence of BaF2 are promising as gain media for broadband near-infrared amplifiers.

Rare earths in lead-free oxyfluoride germanate glasses

Spectroscopic properties of rare earths in lead-free oxyfluoride germanate glasses were studied. The absorption and luminescence spectra of Eu(3+), Pr(3+) and Er(3+) ions were examined as a function of BaF₂ concentration and several spectroscopic parameters for rare earths were determined. The ratio of integrated luminescence intensity of the (5)D₀→(7)F₂ transition to that of the (5)D₀→(7)F₁ transition of Eu(3+) decrease significantly with increasing BaF₂ content. The absorption (Er(3+)) and emission (Pr(3+)) 'hypersensitive transitions' of rare earths are shifted in direction to shorter wavelengths with increasing BaF₂ content in glass composition. Emission spectra and their decays corresponding to the main (4)I₁₃/₂→(4)I₁₅/₂ laser transition of Er(3+) were also analyzed. Quite long-lived NIR luminescence of Er(3+) is observed for lead-free glass samples with low BaF₂ concentration.

Spectroscopy and energy transfer in lead borate glasses doubly doped with Dy(3)(+)-Tb(3+) and Tb(3)(+)-Eu(3+) ions

Lead borate glasses doubly doped with Dy(3)(+)-Tb(3+) and Tb(3+)-Eu(3+) were investigated using optical spectroscopy. Luminescence spectra of rare earths were detected under various excitation wavelengths. The main green emission band due to (5)D4→(7)F5 transition of Tb(3+) is observed under excitation of Dy(3+), whereas the main red emission band related to (5)D0→(7)F2 transition of Eu(3+) is successfully observed under direct excitation of Tb(3+). In both cases, the energy transfer processes from Dy(3+) to Tb(3+) and from Tb(3+) to Eu(3+) in lead borate glasses occur through a nonradiative processes with efficiencies up to 16% and 18%, respectively. The presence of energy transfer process was also confirmed by excitation spectra measurements.

Visible luminescence of dysprosium ions in oxyhalide lead borate glasses

Visible luminescence of Dy(3+) ions in oxyhalide lead borate glasses was examined. Luminescence spectra show two intense bands at 480 nm and 573 nm due to (4)F(9/2)→(6)H(15/2) (blue) and (4)F(9/2)→(6)H(13/2) (yellow) transitions of Dy(3+). Luminescence decays from (4)F(9/2) state and yellow-to-blue luminescence intensity ratios (Y/B) were analysed with PbX(2) (X=F, Cl) content. An introduction of PbX(2) to the borate glass results in the increasing of (4)F(9/2) lifetime and the decreasing of yellow-to-blue luminescence intensity ratio, which is due to reduction of covalency between Dy(3+) and O(2-)/X(-) ions.

Rare earth-doped lead borate glasses and transparent glass-ceramics: structure-property relationship

Correlation between structure and optical properties of rare earth ions in lead borate glasses and glass-ceramics was evidenced by X-ray-diffraction, Raman, FT-IR and luminescence spectroscopy. The rare earths were limited to Eu(3+) and Er(3+) ions. The observed BO(3)↔BO(4) conversion strongly depends on the relative PbO/B(2)O(3) ratios in glass composition, giving important contribution to the luminescence intensities associated to (5)D(0)-(7)F(2) and (5)D(0)-(7)F(1) transitions of Eu(3+). The near-infrared luminescence and up-conversion spectra for Er(3+) ions in lead borate glasses before and after heat treatment were measured. The more intense and narrowing luminescence lines suggest partial incorporation of Er(3+) ions into the orthorhombic PbF(2) crystalline phase, which was identified using X-ray diffraction analysis.

Optical transitions of Eu3+ and Dy3+ ions in lead phosphate glasses

Lead phosphate glasses containing Eu(3+) and Dy(3+) have been studied. Local structure was verified using Fourier transform (FT)-IR spectroscopy. Emission bands of Eu(3+) and Dy(3+) ions in lead phosphate glasses are observed in the visible spectral range, which correspond to 5D0→7F(J) (J=0,1,2,4) and 4F(9/2)→6H(J/2) (J=15,13,11) transitions, respectively. Shorter luminescence decays from excited states of Eu(3+) and Dy(3+0 are due to the presence of PbO in phosphate glass.

Optical properties of lead borate glasses containing Dy(3+) ions

Optical properties of lead borate glasses containing Dy(3+) ions were examined using absorption and luminescence measurements and theoretical calculations based on the Judd-Ofelt framework and the Inokuti-Hirayama model. The luminescence spectra show two characteristic bands at 480 and 573 nm, which are due to (4)F(9/2)-(6)H(15/2) (blue) and (4)F(9/2)-(6)H(13/2) (yellow) transitions of trivalent Dy(3+) ions. The yellow/blue luminescence and its decay were analyzed as a function of activator concentration.

Er-Doped Lead Borate Glasses and Transparent Glass Ceramics for Near-Infrared Luminescence and Up-Conversion Applications

Lead borate based glasses have been analyzed using Raman and infrared spectroscopy. The formation of different borate groups and the direction of BO3 <--> BO4 conversion strongly depends on the PbO- and/or PbF2-to-B2O3 ratio in chemical composition. PbF2-PbO-B2O3 based glasses containing Er3+ ions have been studied after annealing. The orthorhombic PbF2 crystallites are formed during thermal treatment, which was evidenced by X-ray diffraction analysis. Near-infrared luminescence at 1530 nm and green up-conversion at 545 nm have been registered for samples before and after annealing. The luminescence bands correspond to 4I13/2-4I15/2 and 4S3/2-4I15/2 transitions of Er3+ ions, respectively. In comparison to the precursor glasses, the luminescence intensities are higher in the studied transparent oxyfluoride glass ceramics. Simultaneously, the half-width of the luminescence lines slightly decreases. It can be the evidence that a small amount of the Er3+ ions is incorporated into the orthorhombic PbF2 phase.