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In the framework of luminescent rare-earth-doped glasses for near-infrared applications, TiO 2 -containing inorganic glasses have been recently demonstrated to be a promising alternative to commercially used high-phonon SiO 2 -based glasses. This study investigates the effect of TiO 2 concentration on the near-infrared spectroscopic properties of Yb 3+ ions in multicomponent titanate-germanate glasses. A series of glass samples in the xTiO 2 -(60-x)GeO 2 -BaO-Ga 2 O 3 -Yb 2 O 3 system (x ranging from 0 to 50 mol%) were synthesized using the melt-quenching technique. X-ray diffraction analysis confirmed the fully amorphous nature of the fabricated titanate-germanate samples. Fundamental spectroscopic properties of Yb 3+ -doped titanate-germanate system consisting of absorption spectra, near-IR emission spectra, and luminescence decay curves have been determined based on measurement using optical spectroscopy. The intensity of the emission band at 1 µm due to the 2 F 5/2 → 2 F 7/2 laser transition of Yb 3+ ions increases by over 2.3-fold (TiO 2 as the network former) compared to a barium gallo-germanate sample without TiO 2 . Our previous studies indicate that Yb 3+ -doped titanate-germanate glass is a promising optical material and could be successfully applied to laser technology.

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 Tm 3+ and Tm 3+ /Ho 3+ layer profiles. The low alumina content (Al 2 O 3 : 0.03wt%) results in low refractive index modification. The maximum concentrations of the lanthanide oxides were Tm 2 O 3 : 0.18wt % and Ho 2 O 3 : 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 LP 01 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.

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)GeO 2 -xTiO 2 -30BaO-10Ga 2 O 3 and (60-x)GeO 2 -xB 2 O 3 -30BaO-10Ga 2 O 3 (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 GeO 2 . The spectroscopic assignments of titanium ions were performed with excitation and emission spectra compared to the additional sample containing an extremely low content of TiO 2 (0.005 mol%). On the basis of Raman and FT-IR investigations, it was found that increasing the TiO 2 content caused a destructive effect on the GeO 4 and GeO 6 structural units. The Raman spectra of a sample containing a predominantly TiO 2 (50 mol%) proved that the band was located near 650 cm -1 , which corresponded to the stretching vibration of Ti-O in TiO 6 unit. The deconvoluted IR results showed that the germanate glass network consisted of the coexistence of two BO 3 and BO 4 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.

In this paper, the effect of the GeO 2 :TiO 2 molar ratio in glass composition on the spectroscopic properties of germanate glasses was systematically investigated. The visible luminescence bands associated with characteristic 1 D 2 → 3 H 4 (red), 5 S 2 , 5 F 4 → 5 I 8 (green), and 1 D 2 → 3 F 4 (blue) transitions of Pr 3+ , Ho 3+ , and Tm 3+ ions in systems modified by TiO 2 were well observed, respectively. It was found that the luminescence intensity of glasses containing Pr 3+ and Ho 3+ ions increases, whereas, for Tm 3+ -doped systems, luminescence quenching with increasing content of TiO 2 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 GeO 2 :TiO 2 molar ratio. The addition of TiO 2 to system compositions doped with Tm 3+ ions shifts the (x, y) to the center of the CIE diagram. However, chromaticity coordinates evaluated for glasses containing Pr 3+ ions move to a purer red color. Our results confirm that the spectroscopic properties of the studied glasses strongly depend on TiO 2 content. Moreover, it can be stated that germanate-based glass systems modified by TiO 2 can be used for optoelectronics in RGB technology as red (Pr 3+ ), green (Ho 3+ ), and blue (Tm 3+ ) emitters.

Borogermanate glasses singly doped with Dy 3+ ions were synthesized and then studied using the absorption and luminescence spectra. Spectroscopic changes of Dy 3+ ions have been examined for compositional-dependent glasses with various molar ratios GeO 2 :B 2 O 3 . In this work, several spectroscopic parameters of Dy 3+ ions were obtained experimentally and compared to the calculated values from the Judd-Ofelt theory. Luminescence spectra measured for borogermanate glasses consist of blue, yellow and red bands, which correspond to 4 F 9/2 → 6 H 15/2 , 4 F 9/2 → 6 H 13/2 and 4 F 9/2 → 6 H 11/2 transitions of Dy 3+ , respectively. Luminescence lifetimes for the 4 F 9/2 excited state are reduced, whereas the stimulated emission cross-sections for the most intense 4 F 9/2 → 6 H 13/2 yellow transition of Dy 3+ increase with increasing GeO 2 and decreasing B 2 O 3 concentrations in glass-hosts. Quantum efficiency of the 4 F 9/2 (Dy 3+ ) excited state is nearly independent on molar ratios GeO 2 :B 2 O 3 . Attractive spectroscopic properties related to the 4 F 9/2 → 6 H 13/2 transition of Dy 3+ ions are found for borogermanate glasses implying their potential utility for yellow laser action and solid-state lighting technology.

In this work, the synthesis and characterization of Li 2 MgGeO 4 :Ho 3+ ceramics were reported. The X-ray diffraction measurements revealed that the studied ceramics belong to the monoclinic Li 2 MgGeO 4 . Luminescence properties were analyzed in the visible spectral range. Green and red emission bands correspondent to the 5 F 4 , 5 S 2 → 5 I 8 and 5 F 5 → 5 I 8 transitions of Ho 3+ were observed, and their intensities were significantly dependent on activator concentration. Luminescence spectra were also measured under direct excitation of holmium ions or ceramic matrix. Holmium ions were inserted in crystal lattice Li 2 MgGeO 4 , giving broad blue emission and characteristic 4f-4f luminescent transitions of rare earths under the selective excitation of the ceramic matrix. The presence of the energy transfer process between the host lattice and Ho 3+ ions was suggested.

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 TiO 2 -modified germanate glasses co-doped with Yb 3+ /Ln 3+ (Ln = Pr, Er, Tm, Ho) with excellent spectroscopic properties. Glass systems were directly excited at 980 nm (the 2 F 7/2 → 2 F 5/2 transition of Yb 3+ ). We demonstrated that the introduction of TiO 2 is a promising option to significantly enhance the main near-infrared luminescence bands located at the optical telecommunication window at 1.3 μm (Pr 3+ : 1 G 4 → 3 H 5 ), 1.5 μm (Er 3+ : 4 I 13/2 → 4 I 15/2 ), 1.8 μm (Tm 3+ : 3 F 4 → 3 H 6 ) and 2.0 μm (Ho 3+ : 5 I 7 → 7 I 8 ). Based on the lifetime values, the energy transfer efficiencies (η ET ) were estimated. The values of η ET are changed from 31% for Yb 3+ /Ho 3+ glass to nearly 53% for Yb 3+ /Pr 3+ 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.

The results presented in this communication concern visible and near-IR emission of Pr 3+ ions in selected inorganic glasses, i.e., borate-based glass with Ga 2 O 3 and BaO, lead-phosphate glass with Ga 2 O 3 , gallo-germanate glass modified by BaO/BaF 2 , and multicomponent fluoride glass based on InF 3 . Glasses present several emission bands at blue, reddish orange, and near-infrared spectral ranges, which correspond to 4f-4f electronic transitions of Pr 3+ . The profiles of emission bands and their relative intensity ratios depend strongly on glass-host. Visible emission of Pr 3+ ions is tuned from red/orange for borate-based glass to nearly white light for multicomponent fluoride glass based on InF 3 . The positions and spectral linewidths for near-infrared luminescence bands at the optical telecommunication window corresponding to the 1 G 4 → 3 H 5 , 1 D 2 → 1 G 4 , and 3 H 4 → 3 F 3 , 3 F 4 transitions of Pr 3+ are dependent on glass-host matrices and excitation wavelengths. Low-phonon fluoride glasses based on InF 3 and gallo-germanate glasses with BaO/BaF 2 are excellent candidates for broadband near-infrared optical amplifiers. Spectroscopic properties of Pr 3+ -doped glasses are compared and discussed in relation to potential optical applications.

Glasses containing two different network-forming components and doped with optically active ions exhibit interesting properties. In this work, glass systems based on germanium dioxide and boron trioxide singly doped with lanthanides (Eu 3+ ) and transition metals (Cr 3+ ) ions are research subjects. Optical spectroscopy was the major research tool used to record excitation and emission spectra in a wide spectral range for studied systems. The emitted radiation of glasses doped with Cr 3+ ions is dominated by broadband luminescence centered at 770 nm and 1050 nm ( 4 T 2 → 4 A 2 ). Interestingly, the increase of concentration of one of the oxides contributed to the detectable changes of the R-line ( 2 E → 4 A 2 ) of Cr 3+ ions. Moreover, EPR spectroscopy confirmed the paramagnetic properties of the obtained glasses. The influence of molar ratio GeO 2 :B 2 O 3 on spectroscopic properties for Eu 3+ ions is discussed. The intensity of luminescence bands due to transitions of trivalent europium ions as well as the ratio R/O decrease with the increase of B 2 O 3 . On the other hand, the increase in concentration B 2 O 3 influences the increasing tendency of luminescence lifetimes for the 5 D 0 state of Eu 3+ ions. The results will contribute to a better understanding of the role of the glass host and thus the prospects for new optical materials.

This paper deals with broadband near-infrared luminescence properties of lead germanate glass triply doped with Yb 3+ /Er 3+ /Tm 3+ . Samples were excited at 800 nm and 975 nm. Their emission intensities and lifetimes depend significantly on Er 3+ and Tm 3+ concentrations. For samples excited at 800 nm, broadband emissions corresponding to the overlapped 3 H 4 → 3 F 4 (Tm 3+ ) and 4 I 13/2 → 4 I 15/2 (Er 3+ ) transitions centered at 1.45 µm and 1.5 µm was identified. Measurements of decay curves confirm reduction of 3 H 4 (Tm 3+ ), 2 F 5/2 (Yb 3+ ) and 4 I 13/2 (Er 3+ ) luminescence lifetimes and the presence of energy-transfer processes. The maximal spectral bandwidth equal to 269 nm for the 3 F 4 → 3 H 6 transition of Tm 3+ suggests that our glass co-doped with Yb 3+ /Er 3+ /Tm 3+ is a good candidate for broadband near-infrared emission. The energy transfer from 4 I 13/2 (Er 3+ ) to 3 F 4 (Tm 3+ ) and cross-relaxation processes are responsible for the enhancement of broadband luminescence near 1.8 µm attributed to the 3 F 4 → 3 H 6 transition of thulium ions in lead germanate glass under excitation of Yb 3+ ions at 975 nm.

In this work, the series of Tb 3+ /Eu 3+ co-doped xerogels and derivative glass-ceramics containing CaF 2 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 Tb 3+ /Eu 3+ 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, 7 F 6 → 5 L 9 transition of Tb 3+ ), the mutual coexistence of the 5 D 4 → 7 F J (J = 6-3) (Tb 3+ ) and the 5 D 0 → 7 F J (J = 0-4) (Eu 3+ ) luminescence bands was clearly observed. The co-doping also resulted in gradual shortening of a lifetime from the 5 D 4 state of Tb 3+ ions, and the ET efficiencies were varied from η ET = 11.9% (Tb 3+ :Eu 3+ = 1:0.5) to η ET = 22.9% (Tb 3+ :Eu 3+ = 1:2) for xerogels, and from η ET = 25.7% (Tb 3+ :Eu 3+ = 1:0.5) up to η ET = 67.4% (Tb 3+ :Eu 3+ = 1:2) for glass-ceramics. Performed decay analysis from the 5 D 0 (Eu 3+ ) and the 5 D 4 (Tb 3+ ) state revealed a correlation with the change in Tb 3+ -Eu 3+ and Eu 3+ -Eu 3+ interionic distances resulting from both the variable Tb 3+ :Eu 3+ molar ratio and their partial segregation in CaF 2 nanophase.

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 Eu 3+ excitation spectra measurements. Near-IR emission spectra at 1550 nm related to 4 I 13/2 → 4 I 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 4 I 13/2 (Er 3+ ) was proposed. The luminescence lifetime for the 4 I 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 5 D 0 lifetime increases with increasing phonon energy. Our investigations suggest that the values of measured 5 D 0 lifetime equal to radiative lifetimes for all heavy metal oxide glasses.

In this paper, some series of lead borate glasses and glass ceramics singly doped with Dy 3+ 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 4 F 9/2 → 6 H 15/2 (blue), 4 F 9/2 → 6 H 13/2 (yellow) and 4 F 9/2 → 6 H 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 B 2 O 3 /PbO ratios and PbX 2 contents (where X = Cl, F, Br) in glass composition. For glass-ceramics, the chromaticity coordinates are changed significantly under different excitation wavelengths.

The effect of oxide modifiers on multiple properties (structural and spectroscopic) of phosphate glasses with molar composition 60P 2 O 5 -(10-x)Ga 2 O 3 -30MO-xEu 2 O 3 and 60P 2 O 5 -(10-y)Ga 2 O 3 -30MO-yEr 2 O 3 (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 Eu 3+ and Er 3+ ions, respectively. It was found that the value of fluorescence intensity ratio R/O related to 5 D 0 → 7 F 2 (red) and 5 D 0 → 7 F 1 (orange) transition of Eu 3+ 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 Er 3+ ions. Moreover, the 5 D 0 and 4 I 13/2 luminescence lifetimes of Eu 3+ and Er 3+ ions increase with the increasing ionic radius of M 2+ (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 singly doped with transition metal (Cr 3+ ) and rare earth ions (Eu 3+ ) 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 TiO 2 . 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 GeO 2 was partially substituted by TiO 2 ., Competing Interests: The authors declare no conflict of interest.

In the present work, the Tb 3+ /Eu 3+ co-activated sol-gel glass-ceramic materials (GCs) containing MF 3 (M = Y, La) nanocrystals were fabricated during controlled heat-treatment of silicate xerogels at 350 °C. The studies of Tb 3+ → Eu 3+ energy transfer process (ET) were performed by excitation and emission spectra along with luminescence decay analysis. The co-activated xerogels and GCs exhibit multicolor emission originated from 4f n -4f n optical transitions of Tb 3+ ( 5 D 4 → 7 F J , J = 6-3) as well as Eu 3+ ions ( 5 D 0 → 7 F J , J = 0-4). Based on recorded decay curves, it was found that there is a significant prolongation in luminescence lifetimes of the 5 D 4 (Tb 3+ ) and the 5 D 0 (Eu 3+ ) levels after the controlled heat-treatment of xerogels. Moreover, for both types of prepared GCs, an increase in ET efficiency was also observed (from η ET ≈ 16% for xerogels up to η ET = 37.3% for SiO 2 -YF 3 GCs and η ET = 60.8% for SiO 2 -LaF 3 GCs). The changes in photoluminescence behavior of rare-earth (RE 3+ ) dopants clearly evidenced their partial segregation inside low-phonon energy fluoride environment. The obtained results suggest that prepared SiO 2 -MF 3 :Tb 3+ , Eu 3+ GC materials could be considered for use as optical elements in RGB-lighting optoelectronic devices operating under near-ultraviolet (NUV) excitation.

Nanocrystalline transparent BaF 2 :Eu 3+ 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 BaF 2 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 Eu 3+ and their decays were examined in detail. Some spectroscopic parameters of Eu 3+ ions in glass-ceramics containing BaF 2 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 5 D 0 → 7 F 2 electric-dipole transition (ED) and the 5 D 0 → 7 F 1 magnetic-dipole (MD) transition are changed significantly during transformation from xerogels to nanocrystalline BaF 2 :Eu 3+ glass-ceramic materials. The luminescence decay analysis clearly indicates that the measured lifetime 5 D 0 (Eu 3+ ) considerably enhanced in nanocrystalline BaF 2 :Eu 3+ glass-ceramic materials compared to precursor xerogels. The evident changes in luminescence spectra and their decays suggest the successful migration of Eu 3+ ions from amorphous silica network to low-phonon BaF 2 nanocrystals.

The ErF 3 -doped oxyfluoride phospho-tellurite glasses in the (40-x) TeO 2 -10P 2 O 5 -45 (BaF 2 -ZnF 2 ) -5Na 2 O-xErF 3 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 ErF 3 . 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 ErF 3 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 BaF 2 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 ErF 3 (the base glass).

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 Eu 3+ 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 Eu 3+ 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., Competing Interests: The authors declare no conflict of interest.