Erbium-Doped Fluoroborate Glasses for Near Infrared Broadband Amplifiers

Erbium (Er³⁺)-doped alkali lead tellurofluoroborate (RLTB) glasses were prepared and characterized systematically through optical absorption and emission measurements. The emission spectra in the range 450–900 and 1400–1800 nm were recorded by exciting the samples with 532 nm (Nd : YVO₄ crystal) and 514.5 nm (Ar⁺ laser), respectively. Applying Judd–Ofelt analysis, the intensity parameters have been determined using experimental oscillator strengths of absorption bands. From the Judd–Ofelt intensity parameters, some important fluorescence properties such as spontaneous transition probabilities, radiative lifetimes and luminescence branching ratios for the ⁴S_3/2→⁴I_15/2 (0.55 μm), ⁴S_3/2→⁴I_13/2 (0.85 μm), and ⁴I_13/2→⁴I_15/2 (1.54 μm) emission transitions of Er³⁺ ion in RLTB glasses have been calculated. The continuous pumping of the samples results in fast nonradiative decay through ²H_11/2→⁴F_9/2 (~3500 cm⁻¹) transition, which in turn causes the population of Er³⁺ ions from ²H_11/2 state to the higher ⁴F_3/2 state. The emission cross sections determined for the ⁴I_13/2→⁴I_15/2 (1.54 μm) transition using the McCumber theory are in good agreement with the values obtained from the Judd–Ofelt analysis. From evaluated radiative parameters, it is suggested that these RLTB glasses are more suitable candidates for 0.85 and 1.54 μm broadband optical amplifiers.     

Nanocrystal Formation in Glasses Controlled by Rare Earth Ions

Distribution and roles of rare earth ions in fluoride nanocrystals and lead chalcogenide quantum dots formed in glasses are reported. High-resolution transmission electron microscopic analysis and electron energy loss spectroscopic (EELS) analysis showed that oxyfluoride glasses initially form crystals with high Er³⁺ content such as PbErF₅ during heating and gradually form crystals with low Er³⁺ concentration. Amount of PbErF₅ crystals depended upon the initial concentration of Er³⁺ ions in the parent glasses. EELS analysis also showed that Nd³⁺ ions were formed inside PbS quantum dots, supporting the proposition of the formation of Nd-O clusters.     

The influence of different antimony content in Ga-As-Sb-S chalcogenide glass system: Modification of physical & spectroscopic properties and fiber forming ability

In order to improve the fiber drawing performances including the anti-crystallization in fiber drawing process and the mechanical properties, the fourth component of antimony (Sb) was introduced into Ga_0.8As_39.2S₆₀ glass, and a serial Ga_0.8As_39.2-xSb_xS₆₀ (x = 0, 1, 3,5, 7, 9 and 11) novel chalcogenide glasses doped with 3000 ppmw Dy³⁺ ions were prepared. The influences of antimony content on the physical properties, spectroscopic properties and fiber forming ability of glass were investigated. The experiment results indicate that the introduction of moderate antimony into glass effectively improves the fiber drawing performance and the spectroscopic properties of Dy³⁺ ions. The Ga_0.8As_34.2Sb₅S₆₀ composition glass possesses the best performance and it is recommended a good candidate for mid-infrared laser working medium.     

1.53 µm luminescence properties of Er3+-doped K–Sr–Al phosphate glasses

Trivalent erbium (Er³⁺)-doped K–Sr–Al phosphate glasses were prepared and studied their spectroscopic properties as a function of Er₂O₃ concentration. Judd–Ofelt analysis has been carried out for 1.0 mol% Er₂O₃-doped phosphate glass and in turn radiative properties have been evaluated for the excited levels of Er³⁺ ion. The radiative lifetime for the ⁴I_13/2 level was found to be higher for the present glass when compared to other Er³⁺-doped glasses. The Er³⁺-doped glasses exhibit intense near infrared emission at 1.53 µm corresponds to ⁴I_13/2→⁴I_15/2 transition as well as green emission at 546 nm corresponding to ⁴S_3/2→⁴I_15/2 under 980 nm and 488 nm excitations, respectively. The emission cross-section spectrum for 1.0 mol% of Er₂O₃-doped glass has been evaluated using McCumber theory. The gain cross-section has been evaluated as a function of population inversion, which revealed that the lasing action would be achieved at 1.53 µm for a population inversion about 40%. Decay curves for the ⁴I_13/2 level were measured and lifetimes have been determined for the studied glasses. The results indicate that the present glasses could be useful for laser as well as optical amplifiers at 1.53 µm.     

Dy3+‐Doped Selenide Chalcogenide Glasses: Influence of Dy3+ Dopant‐Additive and Containment

This work reports on process‐induced impurities in rare‐earth ion: Dy³⁺‐doped selenide chalcogenide glasses, which are significant materials for active photonic devices in the mid‐infrared region. In particular, the effect of contamination from the silica glass ampoule containment used in chalcogenide glass synthesis is studied. Heat‐treating Dy‐foil‐only, and DyCl₃‐only, separately, within evacuated silica glass ampoules gives direct evidence of silica ampoule corrosion by the rare‐earth additives. The presence of [Ga₂Se₃] associated with [Dy] on the silica glass ampoule that has been contact with the chalcogenide glass during glass melting, is reported for the first time. Studies of 0–3000 ppmw Dy³⁺‐doped Ge_16.5As₉Ga₁₀Se_64.5 glasses show that Dy‐foil is better than DyCl₃ as the Dy³⁺ additive in Ge‐As‐Ga‐Se glass in aspects of avoiding bulk crystallization, improving glass surface quality and lowering optical loss. However, some limited Dy/Si/O related contamination is observed on the surfaces of Dy‐foil‐doped chalcogenide glasses, as found for DyCl₃‐doped chalcogenide glasses, reported in our previous work. The surface contamination indicates the production of Dy₂O₃ and/or [≡Si‐O‐Dy=]‐containing particles during chalcogenide glass melting, which are potential light‐scattering centers in chalcogenide bulk glass and heterogeneous nucleation agents for α‐Ga₂Se₃ crystals.     

Luminescence properties of Sm3+ ions doped heavy metal oxide tellurite-tungstate-antimonate glasses

The trivalent Sm³⁺ ion doped tellurium-antimony-tungsten oxides based glasses were prepared by conventional melt quenching and pressing method. Spectroscopic characterizations such as optical absorption, photoluminescence and decay profile measurements were performed on the glasses. Judd-Ofelt theory is used to evaluate the oscillator strengths and the three phenomenological intensity parameters (Ω_λ, λ = 2, 4, 6) of the glasses. The photoluminescence spectra recorded under 479 nm excitation exhibited the emission bands at 562, 598, 645 and 708 nm corresponding to the transitions ⁴G_5/2 → ⁶H_J (J = 5/2, 7/2, 9/2, 11/2) respectively. Using J-O parameters (Ω_λ) various important radiative parameters viz., transition probabilities, emission cross-sections, branching ratios of various emission bands were evaluated. Decay profiles were recorded to find the lifetime of the ⁴G_5/2 excited level and the obtained life time values are observed to decrease with an increase of Sm³⁺ ion concentration; such decrease is attributed due to clustering of Sm³⁺ ions which may cause luminescence quenching.     

Compositional dependence of the optical properties of novel Ga–Sb–S–XI (XI = PbI2, CsI,AgI) infrared chalcogenide glasses

A novel family of Ga₂S₃–Sb₂S₃–XI (XI = PbI₂, CsI, AgI) was investigated to understand the role of metal halides and exploit new chalco‐halide glasses for infrared optics. The dependence of the thermal properties, infrared optical properties, and structural information of the novel family on different metal–iodines was investigated. Results showed that metal halides increase the glass stability but decrease the glass network connectivity. The compositional dependence of the short‐wave cut‐off edge is associated with the electronegativity difference between the cations and anions of the metal halides. Raman study showed that the metal–iodine modified the glass structure mainly through the iodide content, and the cations dissolved in the glass network mostly as charge compensators for the aperiodic network. For the glasses in the series Ga₂S₃–Sb₂S₃–XI–Dy³⁺, Dy³⁺ emission increased in the PbI₂‐ and CsI‐doped glasses but decreased in the AgI‐doped glass due to the combined effect of dysprosium and oxygen. For all that, these novel glasses are highly promised for use in infrared optics.     

Enhancement of up-conversion emission and emerging cool white light emission in co-doped Yb3+/ Er3+: Li2O-LiF-B2O3-ZnO glasses for photonic applications

A series of co-doped (Yb³⁺/Er³⁺): Li₂O-LiF-B₂O₃-ZnO glasses were prepared by standard melt quenching technique. Structural and morphological studies were carried out by XRD and FESEM. Phonon energy dynamics have been clearly elucidated by Laser Raman analysis. The pertinent absorption bands were observed in optical absorption spectra of singly doped and co-doped Yb³⁺/Er³⁺: LBZ glasses. We have been observed a strong up-conversion red emission pertaining to Er³⁺ ions at 1.0 mol% under the excitation of 980 nm. However, the up-conversion and down conversion (1.53 µm) emission intensities were remarkably enhanced with the addition of Yb³⁺ ions to Er³⁺: LBZ glasses due to energy transfer from Yb³⁺ to Er³⁺. Up-conversion emission spectra of co-doped (Yb³⁺/Er³⁺): LBZ glasses exhibits three strong emissions at 480 nm, 541 nm and 610 nm which are assigned with corresponding electronic transitions of ²H_9/2 → ⁴I_15/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 respectively. Consequently, the green to red ratio values (G/R) also supports the strong up-conversion emission. The Commission International de E′clairage coordinates and correlated color temperatures (CCT) were calculated from their up-conversion emission spectra of co-doped (Yb³⁺/Er³⁺): LBZ glasses. The obtained chromaticity coordinates for optimized glass (0.332, 0.337) with CCT value at 5520 K are very close to the standard white colorimetric point in cool white region. These results could be suggested that the obtained co-doped (Yb³⁺/Er³⁺): LBZ glasses are promising candidates for w-LEDs applications.     

Effect of BaF2 Content on Luminescence of Rare‐Earth Ions in Borate and Germanate Glasses

Rare‐earth‐doped oxyfluoride germanate and borate glasses were synthesized and next studied using spectroscopic methods. Influence of fluoride modifier on luminescence properties of rare earths in different glass hosts was examined. The excitation and emission spectra of Pr³⁺ and Er³⁺ ions in the studied glasses were registered. The emission spectra of Pr³⁺ ions in germanate and borate glasses are quite different and depend strongly on the glass host. In samples doped with Er³⁺ ions emission bands located around 1530 nm corresponding to the main ⁴I_13/2→⁴I_15/2 laser transition were registered, independently of the glass host. Quite long‐lived near‐infrared luminescence of Er³⁺ ions was observed for germanate glasses with low BaF₂ content, while in borate glass systems influence of barium fluoride on luminescence lifetimes is not so evident. The Judd–Ofelt calculations were used in order to determine quantum efficiencies of excited states of rare‐earth ions in germanate and borate glasses.     

Optical and Judd-Ofelt spectroscopic study of Er3+-doped strontium gadolinium gallium garnet single-crystal

Er³⁺-doped strontium gadolinium gallium garnet (SrGdGa₃O₇) single-crystal was grown by Czochralski method. The Er³⁺ concentration in the crystal was determined as 4.2 × 10²¹ ions/cm³ by inductively coupled plasma atomic absorption spectroscopy. Refractive index of the crystal was measured at the wavelengths of 633, 1311 and 1553 nm by prism coupling technique. The results show that the crystal is a positive uniaxial crystal with a birefringence of ~0.01, and the Sellmeier equation reported previously for the crystal doped with Nd³⁺ is also valid for the one doped with Er³⁺. Unpolarized absorption spectrum of the crystal was measured at room temperature and the Er³⁺ absorption cross-section spectrum was calibrated from it. The Er³⁺ spectroscopic properties were studied by Judd-Ofelt theory. Some fundamental spectroscopic parameters were obtained that include absorption coefficient and cross-section spectral distributions, electronic transition oscillator strength, Judd-Ofelt parameters, fluorescence branch ratio, transition probability, radiative and fluorescence lifetimes, and quantum efficiency.     

Spectral properties of glass (15Ga<Subscript>2</Subscript>S<Subscript>3</Subscript> · 85GeS<Subscript>2</Subscript>) doped with erbium

For chalcogenide glasses in the system (1 – x)[0.15Ga₂S₃ · 0.85GeS₂] · xEr₂S₃, the absorption and luminescence spectra are investigated and the X-ray diffraction analysis is performed. A small shift in the position of the erbium absorption band with the increase of its content in the glass indicates the decrease of the effective charge on it, while the negligible changes in the angle position of the first sharp diffraction peak points to the constancy of the glass’s intermediate-order parameter. The possibility of describing the dependence of the intensity of erbium luminescence on its concentration using the earlier suggested equation has been discussed.     

Structure and optical properties of Er‐doped CaO‐Al2O3 (Ga2O3) glasses fabricated by aerodynamic levitation

We fabricated a series of stable Er‐doped CaO‐Al₂O₃(Ga₂O₃) glasses by aerodynamic levitation (ADL) method. Using thermal analysis, we studied the influence of composition on the thermal stability of the glasses. The results unraveled the significance of composition on the stability of glasses. Magic angle spinning nuclear magnetic resonance (MAS‐NMR) and Raman spectra were used to analyze the glass microstructure. The optical and spectroscopic properties were examined by UV‐Vis absorption, steady‐state fluorescence spectroscopy, transient state fluorescence spectroscopy, and luminescence quantum yield measurements. The results unraveled a clear concentration‐dependent up‐conversion and NIR emissions of Er³⁺, with obvious spectral broadening and redshift. The related mechanisms of decrease in fluorescent lifetime (from about 9 ms to 2 ms) and quantum yield (from about 75% to 5%) are discussed.     

Intense broadband 3.1 μm emission in Er3+-doped fluoroaluminate-tellurite glass for mid-infrared laser application

Er³⁺ single doped fluoroaluminate-tellurite glasses were made by employing a conventional melt-quenching technique. A strong fluorescence around 3.1 μm was achieved from Er³⁺-doped fluoride glasses, under a 980 nm laser diode pump, which was assigned to the Er³⁺: ⁴S_3/2 → ⁴F_9/2 radiation transition process. The up-conversion and mid-infrared spectra of emission for fluoroaluminate-tellurite glasses with various concentrations of Er³⁺ ions dopant was researched. In addition, the calculated fluorescence lifetime value about 3.1 μm reaches 0.48 ms. The findings indicate that fluoroaluminate-tellurite glasses doped with Er³⁺ have prospects of being developed into 3.1 μm mid-infrared fiber and laser materials.     

Intense 2.7 µm emission of Er3+/Pr3+ doped Ga5Ge20Sb10S65 chalcogenide glass

There are numerous vital usages for mid-infrared (MIR) lasers in satellite communication, biomedicine, military, remote sensing, and environmental monitoring. In this work, a progression of Er³⁺ ions doped, Er³⁺/Pr³⁺ ions co-doped Ga₅Ge₂₀Sb₁₀S₆₅ glasses were prepared, and their physical performances and structural characteristics were examined. To understand the non-phonon-assisted energy transfer mechanism, we recorded the up-conversion and infrared fluorescence emission spectra by pumping with a commercial 980 nm LD. Then the 2.7 µm strong fluorescence signal intensity can be obtained when the doped concentration of Pr³⁺ is proper. After the doping of Pr³⁺, fluorescence lifetime results revealed that the lifetimes of the Er³⁺:⁴I_13/2 level fell dramatically from 7.33 to 1.90 ms, which experienced a much more significant decrease in lifetimes than the Er³⁺:⁴I_11/2 level. The MIR fluorescence performances were assessed by the determined J–O parameters and relative emission cross sections. Additionally, the generally huge emission cross sections and the small pump energy show that it is possible to obtain population inversion with relatively small pump energy; thus the Er³⁺/Pr³⁺ glasses have great potential to be 2.7 µm laser materials.     

Enhanced Up‐Conversion Luminescence in Er3+‐Doped 25GeS2·35Ga2S3·40CsCl Chalcogenide Glass–Ceramics

Enhanced luminescence in rare‐earth‐doped chalcogenide glass–ceramics is of great interest for the potential integrated optoelectronic devices. However, fundamental mechanism on the enhancement of luminescence upon crystallization remains largely unknown. We report the fabrication and characterization of wide transmission chalcogenide glass and glass–ceramics based on the 25GeS₂·35Ga₂S₃·40CsCl:0.3Er glass composition, and discuss the mechanism of enhanced luminescence. By monitoring the ⁴I_9/2–⁴I_15/2 of Er³⁺ transition, up‐conversion luminescence of 12 times higher was observed in glass–ceramics compared with that in base glass. Electron paramagnetic resonance (EPR) and Raman scattering spectroscopies were employed to obtain the information of selective environment of Er³⁺ ions and microstructural evolution with the crystallization progress. Both of them evidenced that the enhanced up‐conversion luminescence was mainly related to the local environmental evolution from a mixed chlorine‐sulfur coordination to a low phonon energy chlorine coordination in the residual glassy matrix of glass–ceramics.     

Correlation Between Crystallization Behavior and Network Structure in GeS2–Ga2S3–CsI Chalcogenide Glasses

Diagram of the phase transformation behavior of GeS₂–Ga₂S₃–CsI glasses is realized in this article and the structure‐property dependence of the chalcogenide glasses is elucidated using differential scanning calorimetry and Raman spectroscopy. We observe the compositional threshold of crystallization behavior locates at x = 6–7 mol% in (100?x)(0.8GeS₂–0.2Ga₂S₃)–xCsI glasses, which is confirmed by the thermodynamic studies. Structural motifs are derived from the Raman result that [Ge(Ga)S₄], [S₂GeI₂], [S₃GaI], and [S₃Ga–GaS₃] were identified to exist in this glass network. Combined with the information of structural threshold, local arrangement of these structural motifs is proposed to explain all the experimental observations, which provides a new way to understand the correlation between crystallization behavior and network structure in chalcogenide glasses.     

A broadband-sensitive upconverter: Garnet-type Ca3Ga2Ge3O12 codoped with Er3+, Y3+, Li+, Ni2+, and Nb5+

We have developed a new broadband-sensitive photon upconversion (UC) material that can be used for transparent ceramic plates mounted on the rear faces of crystalline silicon solar cells. We selected the host material of a cubic crystal structure codoped with Er³⁺ and Ni²⁺ so that the Ni²⁺ dopants were fully activated to sensitize the Er³⁺ emitters. In garnet-type Ca₃Ga₂Ge₃O₁₂ with additional codopants of Nb⁵⁺ and Li⁺ for charge compensation, all the Ni²⁺ dopants occupied the six-coordinated Ga³⁺ sites, leading to highly efficient energy transfer from the Ni²⁺ to the Er³⁺. Formation of four-coordinated Ni²⁺ that quenches the UC emission of the Er³⁺ was prevented, because Ni²⁺ cannot substitute the four-coordinated Ge⁴⁺ much smaller than Ni²⁺. Consequently, energy dissipation from the Er³⁺ to the Ni²⁺ was well reduced compared with the previously developed Gd₃Ga₅O₁₂:Er,Ni,Nb in which the Ni²⁺ dopants partially occupied the four-coordinated Ga³⁺ sites. Additional introduction of Y³⁺ and Li⁺ enhanced optical transitions and improved the UC performance, owing to more enhanced lattice distortion, along with eliminating different phases. The optimal composition (Ca_0.6Er_0.1Y_0.1Li_0.2)₃(Ga_0.98Ni_0.01Nb_0.01)₂Ge₃O₁₂ exhibited a broadband sensitivity ranging from 1.1 μm (the absorption edge of silicon) to 1.6 μm for the UC emission at 0.98 μm.     

First Identification of Rare‐Earth Oxide Nucleation in Chalcogenide Glasses and Implications for Fabrication of Mid‐Infrared Active Fibers

Gallium (Ga) helps solubilize rare‐earth ions in chalcogenide glasses, but has been found to form the dominant crystallizing selenide phase in bulk glass in our previous work. Here, the crystallization behavior is compared of as‐annealed 0–3000 ppmw Dy³⁺‐doped Ge–As–Ga–Se glasses with different Ga levels: Ge_16.5As_(19?x)Ga_xSe_64.5 (at.%), for x = 3 and 10, named Ga₃ and Ga₁₀ glass series, respectively. X‐ray diffraction and high‐resolution transmission electron microscopy are employed to examine crystals in the bulk of the as‐prepared glasses, and the crystalline phase is proved to be the same: Ge‐modified, face centered cubic α‐Ga₂Se₃. Light scattering of polished glass samples is monitored using Fourier transform spectroscopy. When Ga is decreased from 10 to 3 at.%, the bulk crystallization is dramatically reduced and the optical scattering loss decreases. Surface defects, with a rough topology observed for both series of as‐prepared chalcogenide glasses, are demonstrated to comprise Dy, Si, and [O]. For the first time, evidence for the proposed nucleation agent Dy₂O₃ is found inside the bulk of as‐prepared glass. This is an important result because rare‐earth ions bound in a high phonon–energy oxide local environment are, as a consequence, inactive mid‐infrared fluorophores because they undergo preferential nonradiative decay of excited states.     

Deep red upconversion photoluminescence in Er3+-doped Yb3Ga5O12 nanocrystalline garnet

The nanocrystalline single-phase Er³⁺-doped Yb₃Ga₅O₁₂ garnets have been prepared by the sol-gel combustion technique with a crystallite size of ≈30 nm. The presence of Yb³⁺ in garnet hosts allows their efficient excitation at the ≈977 nm wavelength. The Er³⁺ doping of Yb₃Ga₅O₁₂ garnet host results in deep red Er³⁺: ⁴F_9/2 → ⁴I_15/2 upconversion photoluminescence (UCPL) emission. The dominance of the red UCPL emission over the green Er³⁺: ⁴F_7/2/²H_11/2/⁴S_3/2 → ⁴I_15/2 component was investigated using the measurement of the steady-state and time-dependent Er³⁺ and Yb³⁺ emission spectra in combination with the power-dependent UCPL emission intensity. The proposed upconversion mechanism is discussed in terms of the Er³⁺ → Yb³⁺ energy back transfer process as well as Yb³⁺(Er³⁺) → Er³⁺ energy transfer and Er³⁺ ↔ Er³⁺ cross-relaxation processes. The studied Er³⁺-doped Yb₃Ga₅O₁₂ garnet may be utilized as a red upconversion emitting phosphor.     

Mechanism of anti-stokes photoluminescence in Ag0.05Ga0.05Ge0.95S2-Er2S3 glassy alloys

The absorption and up-conversion photoluminescence spectra of alloys of the Ag_0.05Ga_0.05Ge_0.95S_2?x Er₂S₃ system (100 ? x), excited with 980-nm laser irradiation, where x = 0.42, 0.25, and 0.18 mol %, have been studied. Green, intensive red, and infrared luminescence, which is caused by electronic ² H _11/2 → ⁴ I _15/2, ⁴ F _9/2 → ⁴ I _15/2, ⁴ S _3/3 → ⁴ I _13/2 transitions in Er³⁺ ions, respectively, and connected with two photon up-conversion processes was recorded in all samples. The changes in the intensities of glassy alloys of radiation bands with different erbium contents and the influence of large structure defects on the processes of the occupation and the devastation of the energetic levels of erbium ions.