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Band structure and gain in a Ge/Ge1-xSnx/Ge quantum well are described theoretically using a 14-band k.p model. It has been shown that the quantum well width and the α-Sn concentration considerably modify the conduction and valence subband structure, and, as a result, the optical gain changes with the insertion of a very small concentration of α-Sn. In particular, we have determined the necessary injection carrier density Nj and the critical α-Sn concentration for elevated high gain lasing. It is found that for Nj = 1.5 × 1018 cm−3, we achieved a maximum peak gain for α-Sn concentration of the order 0.155. We can predict that Ge/Ge1-xSnx/Ge QWs should be manufactured with an α-Sn concentration less than 0.155 in devices for optoelectronics applications such as telecommunication and light emitting laser diodes. [ABSTRACT FROM AUTHOR]

The mid-infrared emission mechanism of line-and-space structures of metallic plates on dielectric materials is substantiated using high conductive n-doped (n++-) GaN–semi-insulating (SI-) GaN microstripe structures on an SI-GaN epitaxial layer, which was veiled when using line-and-space structures of Au plates. The present structure exhibits a few thermal emission lines originating from electric dipoles resonating with the coherent longitudinal optical (LO) phonon-like lattice vibration, which are formed by the local depolarization electric field in the surface n++-GaN/SI-GaN/n++-GaN regions. The energies of the LO-phonon-like modes shift from the original LO-phonon energy of GaN to the lower energy region, which contrasts with the LO-phonon resonant emission from the microstructures on GaAs. These emission lines have another notable feature, i.e. the observed peak energies are independent of the polar emission angle for both s- and p-polarizations, unlike the emissions by surface phonon polaritons showing a significant directive nature of peak energies. The results show that each peak energy of the present emission lines is positioned at the zero-point of the real part of the electric permittivity comprising the components of the transverse optical phonon and other electric dipoles induced by the LO-like modes, excluding the target mode. The significant peak-energy shift of the LO-like phonons is applicable to materials with wide Reststrahlen bands, which contrasts with that of the nearly LO-phonon resonating feature of materials with narrow Reststrahlen bands, such as GaAs. The peak energy shift depending on the emission direction is observed for Au–GaN stripe structures. This property is ascribed to the imperfect Au/GaN interface with surface states through the theoretical analysis of the modified electric permittivity in the surface region, numerical simulation of the local electric field via finite-difference time-domain calculation, and experimental studies on a Ti–GaN structure and emission peaks originating from an LO-like phonon of the α -Al2O3 substrate. [ABSTRACT FROM AUTHOR]

Chalcogenide and chalcohalide glasses have been considered promising host materials for thermal imaging lenses and mid-infrared (MIR) optical fibers. In this paper, a novel Ga 2 S 3 -SnS 2 -CsI chalcohalide glass system, with environment-friendly constituent elements, was proposed. The glass forming region was explored, and the physical properties were investigated. The glasses show high transmittance (>60%) over the 1–12 μm spectral range and exhibit relatively high microhardness, making them competitive candidates for manufacturing thermal imaging lenses. Furthermore, the MIR emission property of Dy3+-doped Ga 2 S 3 -SnS 2 -CsI glass was also studied. With strong emissions and high quantum efficiencies at 3.00 μm and 4.38 μm wavelengths, the glass can be potentially used as gain media for MIR lasers. [ABSTRACT FROM AUTHOR]

Improving optical performance of fluoride-based glass ceramics is still of great importance to laser gain hosts. In this work, cubic KY 3 F 10 nanocrystals (NCs) precipitated from a simple ternary 60SiO 2 –20YF 3 –20KF fluorosilicate glass matrix have been obtained. The result of element content shows that fluorine element is largely preserved in the precursor glass, in which obvious spontaneous crystallization of KY 3 F 10 NCs occurs. Subsequent heat-treatment upon the glass samples results in the further formation of KY 3 F 10 NCs, exhibiting a maximum crystallinity of 37.5% in GC760 sample. The mid-infrared emission at 2.7 μm is hence enhanced due to the incorporation of Er3+ ions into the KY 3 F 10 NCs with low phonon energy. The corresponding fluorescence lifetimes are prolonged from 0.37 and 6.69 ms to 7.00 and 9.16 ms for the upper 4I 11/2 and lower 4I 13/2 levels, respectively, with the increase of heat-treated temperature. Our results may provide reference data and research ideas for exploring ∼3 μm solid laser gain materials. [ABSTRACT FROM AUTHOR]

The choice of gain media significantly affects the efficiency of mid-infrared (MIR) lasers and amplifiers. Transition metal ion-doped glass-ceramics (GCs) are attractive laser gain materials as they have the advantages of both laser crystals and glasses. Transparent GC fibers with efficient MIR emission are currently scarce. The emission properties of Ni2+ ion in GCs are generally studied in an octahedral ligand field, where it emits near-infrared light. The emission properties of tetra-coordinated Ni2+ ions are yet to be explored. Herein, we found a chalcogenide glass host characterized by high crystallinity and prepared transparent Ni2+-doped chalcogenide GC containing ZnS nanocrystals by in-situ crystallization. Moreover, for the first time, we reported the broadband MIR 3–4 μm emission at room temperature from tetra-coordinated Ni2+ in chalcogenide GC fiber embedded with ZnS nanocrystal. The fiber losses were measured to be 18.6 ± 1.1, 9.8 ± 0.6 and 11.4 ± 0.8 dB/m at 2.10, 3.39 and 3.80 μm, respectively. The results indicate that the active chalcogenide GC fiber reported herein can be potentially used to develop MIR-tunable fiber lasers and amplifiers. [ABSTRACT FROM AUTHOR]

Silicon carbide (SiC) particles are exciting structures because of their hardness, chemical inertness, and dielectric properties. In particular, their absorption/emission properties in the mid‐infrared range render them suitable structures for ambient temperature thermal emitters. However, the synthesis of uniform, spherical structures is still challenging. Here, we present a robust synthesis procedure based on carbothermal reduction of silica precursor particles. With an isotropic shrinkage of ∼30 %, the spherical particle shape and uniformity are retained. Furthermore, we outline the influence of the gas atmosphere during the carbothermal treatment and demonstrate the successful conversion to SiC by electron microscopy, X‐ray diffraction, thermal and optical analysis. [ABSTRACT FROM AUTHOR]

Pursuing low-phonon-energy (LPE) host for high luminescent efficiency of the doped active ions has stimulated the development of chalcohalide glass and the related nanocomposite via glass crystallization. In this work, a kind of chalcohalide devitrified glass (DG) containing BaCl 2 :Tm3+/Er3+ nanocrystals (NCs) were fabricated during glass melt-quenching. Interestingly, the DG yields some uncommon upconversion (UC) emission lines and enhanced UC/downshifted luminescence compared with the sample free of BaCl 2 , thanks to the partition of rare earth ions into the LPE environment of BaCl 2. There is an efficient energy transfer between Tm3+ and Er3+, whereupon Tm3+ doping enhances Er3+ 2.7 μm mid-infrared (MIR) emission by 1.85 times. Importantly, a distinctive viewpoint is proposed to understand the MIR enhancing mechanism, involving the reduction in cross relaxation (CR) processes among Er3+ ions via Tm3+ doping. • A new viewpoint for the enhanced Er3+ mid-infrared emission upon Tm3+ doping. • BaCl 2 nanocrystals precipitates from glass matrix during melt-quenching. • Rare earth ions partitioned into BaCl 2 nanocrystals with low phonon energy. • Some uncommon upconversion emission lines of Er3+ and Tm3+ are identified. [ABSTRACT FROM AUTHOR]

Tunable mid-infrared emission is highly applicable in the fields of molecular spectroscopy and atmospheric monitoring. Recent studies have demonstrated that external electric fields can induce non-zero optical bandgaps of up to 250 meV in graphene materials, thereby paving the way for mid-infrared emissions (3–14 μm) to be realized. Graphene foam (GF) possesses a unique highly porous microstructure, which allows intense reflection or scattering of incident photons and gives rise to efficient interband optical absorption. Enhanced electron–phonon coupling enables free electrons in the conduction band to relax non-radiatively to the 1s-state. Mid-infrared emission is generated owing to electron–hole recombination. In this work, we demonstrate the induction of widely tunable (2.9–8.6 μm) mid-infrared emission in GF by modulated visible laser diode (LD) light with modulation frequencies ranging from 1.5 to 0.5 kHz. The peak emission wavelength correlates with the modulation frequency and is independent of the wavelength of LD light of visible range, whereas the emission intensity is related to the alternating intensity of the LD. Our findings indicate that GF is not only a novel mid-infrared emitting material, but one that promises bandgap flexibility for widely tunable mid-infrared sources. [Display omitted] [ABSTRACT FROM AUTHOR]

In this work, we have performed a comprehensive investigation of the Ag+ concentration effect on the morphological, thermal, structural, and mid-infrared emission properties of novel oxyfluoride borosilicate glasses and glass ceramics containing both Ag nanoparticles and erbium-doped hexagonal NaYF4 nanocrystals. The effect of Ag+ ions on the glass forming and crystallization processes was discussed in detail by glass structural analysis. It was found that the Ag+ concentration can affect the distribution of Na+ ion and bridge oxygen in boron-rich and silicon-rich phases, which induced the transformation between BO3 triangles and BO4 tetrahedra during crystallization process. In addition, there was a turning point when the doped Ag+ ion concentration reached its solubility in the borosilicate glass. Furthermore, the enhancement of the 2.7 μm emission and the reduction of the lifetime of the 4I13/2 level were observed both in glasses and in glass ceramics, and its origin was revealed by qualitative and quantitative analyses of the Er3+-Ag nanoparticles (localized electric field enhancement) and Er3+-Er3+ (nonradiative resonance energy transfer) interactions within glasses and glass ceramics. Moreover, the high lifetime of the 4I11/2 level (2.12 ms) and the peak emission cross section in 2.7 μm (6.8×10−21 cm2) suggested that the prepared glass ceramics have promising mid-infrared laser applications.

Tunable and ultrabroadband mid-infrared (MIR) emissions in the range of 2.5–4.5 μm are firstly reported from Co2+-doped nano-chalcogenide (ChG) glass composites. The composites embedded with a variety of binary (ZnS, CdS, ZnSe) and ternary (ZnCdS, ZnSSe) ChG nanocrystals (NCs) can be readily obtained by a simple one-step thermal annealing method. They are highly transparent in the near- and mid-infrared wavelength region. Low-cost and commercially available Er3+-doped fiber lasers can be used as the excitation source. By crystal-field engineering of the embedded NCs through cation- or anion-substitution, the emission properties of Co2+ including its emission peak wavelength and bandwidth can be tailored in a broad spectral range. The phenomena can be accounted for by crystal-field theory. Such nano-ChG composites, perfectly filling the 3–4 μm spectral gap between the oscillations of Cr2+ and Fe2+ doped II VI ChG crystals, may find important MIR photonic applications (e.g., gas sensing), or can be used directly as an efficient pump source for Fe2+: II VI crystals which are suffering from lack of pump sources. [ABSTRACT FROM AUTHOR]

Mid‐infrared (MIR) fiber lasers have wide application prospects and great commercial value in the fields of medical operation, remote sensing and military weapon, etc. At present, Tm3+‐doped glass can obtain broadband luminescence at 2 μm, the introduction of Ho3+ or Er3+ ions also shows a tunable MIR emission but with limited success. Herein, the rare‐earth (RE) doped glass with quantum dots (QDs) precipitation is proposed for achieving ultra‐broadband MIR emissions. The types and sizes of QDs are determined by the XRD and TEM, and their optical properties are further characterized by the absorption and emission spectra as well as the lifetime decay curves. It is found that the diameter of the QDs is gradually increased from 1.7 to 5.1 nm by increasing the heat‐treated temperature from 490°C to 530°C, respectively. Interestingly, an ultra‐broadband emission covering 1400‐2600 nm is achieved from the heat‐treated glass upon the excitation of 808 nm laser diode as a result of an overlapped emission from Tm3+ and PbS. All results suggest that these QDs‐precipitated RE‐doped glasses have important application prospects in ultra‐broadband MIR laser glass, glass fiber, and fiber lasers. [ABSTRACT FROM AUTHOR]

Black phosphorus (BP) is a narrow bandgap (∼0.3 eV) semiconductor with a great potential for optoelectronic devices in the mid-infrared wavelength. However, it has been challenging to achieve a high-quality scalable BP thin film. Here we present the successful synthesis of optically active BP films on a centimeter scale. We utilize the pulsed laser deposition of amorphous red phosphorus, another allotrope of phosphorus, followed by a high-pressure treatment at ∼8 GPa to induce a phase conversion into BP crystals. The crystalline quality was improved through thermal annealing, resulting in the observation of photoluminescence emission at mid-infrared wavelengths. We demonstrate high-pressure conversion on a centimeter scale with a continuous film with a thickness of ∼18 nm using a flat-belt-type high-pressure apparatus. This synthesis procedure presents a promising route to obtain optical-quality BP films, enabling the exploration of integrated optoelectronic device applications such as light-emitting devices and mid-infrared cameras on a chip scale.

We report a detailed spectroscopic investigation of a series of fluorotellurite glasses with different Er 3+ ions concentration in system 50TeO 2 -27BaF 2 -9ZnF 2 -8YF 3 -3MgF 2 -3NaF-xErF 3 -1HoF 3 (x = 1,2,3 mol%). Intense 2 μm emission and 2.75 μm emission with high absorption and emission cross-section were observed under 980 nm LD pumping, and the maximum gain coefficient around 2750 nm was as high as 2.41 cm −1 , suggesting the prepared glasses are a competitive candidate for mid-infrared laser materials. Besides, it was found that the trend of 2 μm and 2.75 μm emission intensity varied with Er 3+ ions concentration was different. Energy transfer process was discussed subsequently to explain this phenomenon. Furthermore, we quantitatively investigate the energy transfer efficiency from Er 3+ : 4 I 13/2 level to Ho 3+ : 5 I 7 level. [ABSTRACT FROM AUTHOR]

In this work, we have performed a comprehensive investigation of the Ag+ concentration effect on the morphological, thermal, structural, and mid-infrared emission properties of novel oxyfluoride borosilicate glasses and glass ceramics containing both Ag nanoparticles and erbium-doped hexagonal NaYF4 nanocrystals. The effect of Ag+ ions on the glass forming and crystallization processes was discussed in detail by glass structural analysis. It was found that the Ag+ concentration can affect the distribution of Na+ ion and bridge oxygen in boron-rich and silicon-rich phases, which induced the transformation between BO3 triangles and BO4 tetrahedra during crystallization process. In addition, there was a turning point when the doped Ag+ ion concentration reached its solubility in the borosilicate glass. Furthermore, the enhancement of the 2.7 μm emission and the reduction of the lifetime of the 4I13/2 level were observed both in glasses and in glass ceramics, and its origin was revealed by qualitative and quantitative analyses of the Er3+-Ag nanoparticles (localized electric field enhancement) and Er3+-Er3+ (nonradiative resonance energy transfer) interactions within glasses and glass ceramics. Moreover, the high lifetime of the 4I11/2 level (2.12 ms) and the peak emission cross section in 2.7 μm (6.8×10−21 cm2) suggested that the prepared glass ceramics have promising mid-infrared laser applications. [ABSTRACT FROM AUTHOR]

Abstract: Highly Er3+‐doped La2O3–Ga2O3 glasses up to ≈5.85 × 1021 cm−3 in Er3+ concentration are synthesized by an aerodynamic levitation technique. The glasses are characterized by high glass‐transition temperatures, low OH− absorptions, and long infrared cut‐off wavelengths. Judd–Ofelt analysis reveals a large radiative transition rate and a high branching ratio of the 4I11/2 → 4I13/2 transition, e.g., 46 s−1 and 21%, respectively, at 10 mol% Er2O3. The intensity of 2.7 µm emission drastically increases with increasing Er2O3 content and reaches a maximum at 10 mol% Er2O3. By contrast, the intensity of the 1.5 µm emission decreases with increasing Er2O3 content when the Er2O3 content is greater than 1 mol%. The emission cross‐section and the gain bandwidth at 2.7 µm are as large as 9.05 × 10−21 cm2 and 9.19 × 10−26 cm3 at 10 mol% Er2O3, respectively. The upconversion spectra also indicate that the investigated glasses exhibit small multiphonon relaxation rates and large quenching concentrations. [ABSTRACT FROM AUTHOR]

This investigation proposes Tb3+ ions as efficient sensitizers of 5–6 μm Nd3+ emission in selenide glasses. Tb3+ ions can be pumped by 2.9 μm Er:YAG as well as by 1.9–2 μm Tm3+ lasers and laser diodes. It was shown, that at room temperature the radiationless energy transfer from Tb3+ to Nd3+ is combined with the reverse process. At liquid nitrogen temperature the energy transfer from Tb3+ to Nd3+ becomes irreversible. The proposed sensitization scheme should allow the development of neodymium chalcogenide glass lasers emitting at ∼6 μm. • Optically excited Tb3+ ions transfer excitation energy to Nd3+ ions. • Nd3+ ions in selenide glass emit at 5–6 μm due to radiationless energy transfer from Tb3+ ions. • Nonradiative energy transfer from Tb3+ to Nd3+ ions in selenide glass becomes irreversible at liquid nitrogen temperature. [ABSTRACT FROM AUTHOR]

A new kind of fluoro-chloride glass was successfully prepared based on fluoroaluminate glass modified by various Cl − . The reductions of phonon density and OH − content revealed by the measured Raman and FTIR spectra show that structural changes caused by the Cl − ions have an effect on the optical properties. With increasing chloride content, the thermal stability factor ΔT showed an increase trend, indicating a better thermal stability of the host. Meanwhile, according to Judd-Ofelt calculation, the intensity parameter Ω 2 increased, which indicates a stronger covalency and local asymmetry of the coordination bonds around the Er 3+ ions after introduction of Cl − . Noticeably, the lifetime (3.48 ms) of Er 3+ : 2.7 μm obtained in the chloride-rich glass (AYF-8Cl) is the longest in reported glass systems, along with obvious enhanced fluorescence intensity. All the results suggested that the fluoro-chloride glasses hint its potential applications in laser materials, especially in 3 μm wavelength. [ABSTRACT FROM AUTHOR]

The Ho 3+ /Yb 3+ co-doped (Y 0.9 La 0.1 ) 2 O 3 were prepared by conventional ceramic processing and the optical properties were investigated. The high transparent ceramic showed large absorption cross section at 980 nm (0.84 × 10 –20 cm −2 ), J–O intensity parameter Ω 2 (5.33 × 10 –20 cm −2 ) and spectroscopic quality factor value, which indicate the (Y 0.9 La 0.1 ) 2 O 3 ceramics are an excellent host material. The energy transfer between Yb 3+ and Ho 3+ was also demonstrated and the energy transfer efficiency was 99% for 2% Ho: (Y 0.9 La 0.1 ) 2 O 3 ceramic. In addition, the mid-infrared and near-infrared spectra displayed broad emission band and the mid-infrared emission cross-section increased as a function of Ho 3+ concentration. The results suggest that the Ho 3+ /Yb 3+ :(Y 0.9 La 0.1 ) 2 O 3 transparent ceramic is a potential host material for mid-infrared emission lasers. [ABSTRACT FROM AUTHOR]

Er-doped (K 0.5 Na 0.5 ) 1− x Li x Nb 1− x Bi x O 3 (0.05 ≤ x ≤ 0.08) ceramics have been prepared by pressureless sintering. Because of the cubic-like phase as well as the dense and fine-grained structure, the ceramics are optically clear, exhibiting high transmittances in the near-infrared and mid-infrared (MIR) regions (∼50% and ∼75%, respectively). They also possess strong electro-optic (EO) response, giving a large effective linear EO coefficient (128–184 pm/V). Owing to Er 3+ , the ceramics exhibit green and red up-conversion photoluminescence (PL) emissions, which are sensitive to the crystal symmetry of the ceramic host. The ceramics also exhibit a low absorption coefficient of OH − groups and then distinct and broadband MIR emissions. Together with the relatively large piezoelectric coefficient (70–90 pC/N), high dielectric constant (∼1400) and low dielectric loss (∼0.03), the ceramics open up potential applications in electrical/optical interdisciplinary field, such as visible displays, MIR solid lasers and optical attenuators. [ABSTRACT FROM AUTHOR]

We perform the spectral analysis of fresh leaves using light-induced mid-IR emission spectroscopy (LIMIRES), a technique utilizing CW optical pumping for preparing and monitoring vibrationally excited states of chromophores. We show how to obtain high-quality IR-emission spectra of intact leaves using visible light of low intensity and sensitive Fourier transform infrared spectroscopy (FTIR). Changing the conditions of illumination, we carry out the spectral discrimination between leaf samples of wild plants and transgenic tobacco plants. Our results show that LIMIRES is a valuable new technique for studying the vibrational structure of excited pigments as well as the nondestructive monitoring of the quality of tobacco leaves. [ABSTRACT FROM AUTHOR]

Y 3+ /Er 3+ ions co-doped oxyfluoride glass-ceramics were investigated to realize efficient 2.7 μm emission. Incorporation of Er 3+ ions into the fluoride nanocrystals was confirmed by the X-ray diffraction patterns, absorption spectra, emission spectra and Judd-Ofelt analysis. With an increase in the Y 3+ /Er 3+ ratio, radiative lifetime, quantum efficiency and emission cross section of the 2.7 μm emission from Er 3+ ions were greatly improved, due to the reduced effective concentration of Er 3+ ions and suppressed cross relaxation processes among Er 3+ ions in the fluoride nanocrystals. Compared to other Er 3+ -doped glasses, Y 3+ /Er 3+ co-doped oxyfluoride glass-ceramics showed a promising potential for gain medium. [ABSTRACT FROM AUTHOR]

Spectroscopic property and energy transfer processes of singly doped and codoped Er 3+ and Nd 3+ fluoroaluminate glasses with low phosphate content are systematically analyzed. The absorption spectra of these glasses are tested, and the Judd–Ofelt (J–O) and radiative parameters are discussed based on J–O theory and the parameters changes substantially because of the other codoping ions. As for Nd 3+ : the main emission bands at 0.9 and 1.05 μm decrease in the codoped sample under the excitation of an 800 nm laser diode from the emission spectra because the Er 3+ : 4 I 11/2 level reduces the Nd 3+ : 4 F 3/2 level effectively through the energy transfer process Nd 3+ : 4 F 3/2 → Er 3+ : 4 I 11/2 . For Er 3+ , the emission at 1.5 μm is restrained by codoping with Nd 3+ ions from the energy transfer process Er 3+ : 4 I 13/2 → Nd 3+ : 4 I 15/2 . The emission at 2.7 μm is enhanced because the Nd 3+ ions deplete the lower level and exert a positive effect on the upper laser level. The microparameters of the energy transfer between the Er 3+ and Nd 3+ ions are calculated and discussed using Forster–Dexter theory. The energy transfer efficiencies of the Nd 3+ : 4 F 3/2 to the Er 3+ : 4 I 11/2 and the Er 3+ : 4 I 13/2 to the Nd 3+ : 4 I 15/2 are 28.8% and 74.5%, respectively. These results indicate that Nd 3+ can be an efficient sensitizer for Er 3+ to obtain Mid-infrared (Mid-IR) emission and the codoped Er 3+ /Nd 3+ fluoroaluminate glass with low phosphate content is suitable to be used as the fiber optical gain media for 2.7 μm laser generation. [ABSTRACT FROM AUTHOR]

Abstract: Ho3+/Er3+:CaYAlO4 and Eu3+/Er3+:CaYAlO4 co-doped crystals were grown by Czochralski method. A detailed spectra analysis such as absorption spectra, up-conversion fluorescence, near-infrared and mid-infrared fluorescence spectra as well as luminescence decay curves was measured in order to optimize the deactivator for mid-infrared (2.7μm) emission in Er3+: CaYAlO4 crystal. The influence of different deactivators on the spectra characteristics was studied. The energy transfer mechanisms, the related energy transfer coefficients and the stimulated emission cross-section were determined. Results show Ho3+ ion is the more appropriate deactivator than Eu3+ ion with which self-termination bottleneck effect was effectively suppressed. All imply that Ho3+ co-doping is beneficial for achieving 2.7μm emission in Er3+:CaYAlO4 crystal. [Copyright &y& Elsevier]

Highlights: [•] An Er3+/Tm3+/Pr3+ triply doped LiYF4 single crystal with high quality has been grown by Bridgman method. [•] An enhanced emission from 2600nm to 2800nm was obtained. [•] The energy transfer mechanism of 2.7μm emission between Er3+, Tm3+ and Pr3+ ions was analyzed. [Copyright &y& Elsevier]

Abstract: Emission properties were investigated in the infrared region for Ga2S3-GeS2-Sb2S3 glasses doped with Ho3+. We performed Judd–Ofelt analysis and lifetime measurements of the 5 I 4, 5 I 5, and 5 I 6 levels, which are the initial levels of the mid-infrared emissions between 3 to 5μm of Ho3+. The quantum efficiencies reached approximately 18%, 64%, and ∼100% for the 5 I 4, 5 I 5, and 5 I 6, respectively. Population analyses were carried out from the relative intensities of the emissions in the near-infrared region. We investigated the dependences on the Ho3+ ion concentration of the population ratio of the initial levels to the final levels, [initial]/[final], of the mid-infrared emissions. The population ratio of [5 I 5]/[5 I 6] decreased with increase of the Ho3+ concentration while those of [5 I 4]/[5 I 5] and [5 I 6]/[5 I 7] increased. Particularly, the former, [5 I 4]/[5 I 5], rapidly increased because of the strong concentration quenching of the 5 I 5 level through cross relaxation. It was found that the population inversion for the 4.8μm emission due to the transition, 5 I 4→5 I 5, was achieved at high Ho3+ concentration in the present experiments. [Copyright &y& Elsevier]

Abstract: We present spectroscopic studies on the ∼5μm mid-infrared emission and energy transfer properties of Tb3+ doped KPb2Br5 and Nd3+ doped KPb2Br5 sensitized by Tm3+ ions. A series of co-doped Tm, Tb: KPb2Br5 and Tm, Nd: KPb2Br5 samples were prepared from purified starting materials of PbBr2, KBr, and rare-earth bromides. Resonant excitation into the 3H6 → 3F4 absorption transition of Tm3+ at ∼1.76μm resulted in an enhanced 5μm emission from Tb3+ and Nd3+ ions in Tm, Tb: KPb2Br5 and Tm, Nd: KPb2Br5, respectively. The existence of energy transfer between Tm→Tb and Tm→Nd in KPB was further evidenced by the quenching of the emission decay times of the 3F4 → 3H6 transition of Tm3+ in doubly doped Tm, Tb: KPb2Br5 and Tm, Nd: KPb2Br5 compared to singly doped Tm: KPb2Br5. [Copyright &y& Elsevier]

An optimal design of two dimensional (2D) hexagonal photonic bandgap (PBG) resonating micro-optical defect cavity on IV-VI lead salt material has been carried out. The nature of both the transverse electric (TE) and transverse magnetic (TM) band structure for the electromagnetic waves in the periodic triangular lattice pattern is formulated by the well-established plane wave expansion (PWE) method. The defect cavity is engineered to resonate at ~4.17 µm in TM bandgap. The field distribution in the defect cavity has been analyzed based on two very efficient and popular schemes - perturbation correction finite difference (FD) method and finite difference time domain (FDTD) mechanism which is truncated by uniaxial perfectly matched layer (UPML) absorbing boundary condition (ABC). FD method efficiently solves Helmholtz equations to evaluate the field distribution in the semiconducting waveguide for any single spectral wavelength. The numerical results by FD method are re-established by the FDTD scheme that incorporates a precise numerical analysis within a specified wavelength range. [ABSTRACT FROM AUTHOR]

Transparent oxyfluoride glass ceramics (GCs) comprised of a uniform oxide glass phase and a well-distributed fluoride crystal phase are regarded as suitable optical gain materials because of the combination of facile fabricability of glass and low phonon energy of nanocrystals. Here, oxyfluoride GCs containing NaYF 4 : Er3+/Ho3+/Dy3+ nanocrystals were controllably prepared. Due to the preferential incorporation of rare-earth ions into NaYF 4 nanocrystals with low phonon energy and the efficient energy transfer between active ions, enhanced and broadband mid-infrared (MIR) emission at 2.5–3.3 µm was obtained from the GCs, which was nearly unobserved in precursor glass (PG) because of the high phonon energy of glass matrix. Compared with Er3+ singly-doped sample, the full width at half maximum (FWHM) is more than 3 times broader in Er3+/Ho3+/Dy3+ triply-doped sample. Furthermore, by the match of the refractive index of glass with NaYF 4 nanocrystal, transparent GCs with average crystal size of 80 nm and high transmittance over 80% were achieved simultaneously. The desirable optical properties endow the GCs with potential applications in MIR broadband tunable lasers. • Enhanced and broadband MIR emission at 2.5–3.3 µm in glass ceramics (GCs) are achieved. • The FWHM of the MIR emission is broadened more than 3 times after co-doping. • GCs with average crystal size of 80 nm and high transmittance over 80% are obtained. • The transmittance of GCs is theoretically analyzed based on Mie scattering theory. [ABSTRACT FROM AUTHOR]

We have demonstrated mid-infrared emission from the self-assembled InAs quantum dots grown on InP substrate by metal-organic vapor phase epitaxy using low toxic tertiarybutylarsine and tertiarybutylphosphine as group V sources in pure nitrogen ambient. Emission wavelength of the InAs quantum dots has been extended to mid-infrared region by embedding the InAs quantum dots in graded InxGa1-xAs matrix layers. When compared with that of the InAs quantum dots grown on lattice matched In0.53Ga0.47As/InP matrix, emission wavelength of the InAs quantum dots red shifted by up to 370 nm when embedded the InAs quantum dots in graded In0.53rarr0.8Ga0.47rarr0.2As barriers. The longest emission wavelength of >2.35 mum from the self-assembled InAs quantum dot structure has been measured at 77 K. The full-width at half-maximum of the photoluminescence emission spectrum of the InAs quantum dots is as narrow as 25.5 meV. The results achieved would be promising to high performance mid-infrared quantum dot lasers on InP substrate [ABSTRACT FROM PUBLISHER]

The properties of InAs/In 0.53 Ga 0.37 As triangular quantum wells (QWs) grown on an InP/SiO 2 /Si integrated substrate by ion-slicing technology are investigated. The material structure and growth quality are characterized by the X-ray diffraction (XRD) and transmission electron microscope measurements. The photoluminescence (PL) spectra at various temperatures are also analyzed. The PL peak wavelengths red-shift from 1.94 to 2.13 μm with the increase of temperature from 12.4 to 300 K. The experimental results of the QWs on InP/SiO 2 /Si substrate are found to be comparable with the performance of the same QWs grown on an InP substrate. The results are promising for future integration of Si with InP-based optical devices for the applications of light emission in mid-infrared wavelength range. [ABSTRACT FROM AUTHOR]

Rare-earth ions doped fiber lasers at 2 µm can supply various applications in daily life. In this paper, Ho3+/Yb3+ co-doped tellurite glasses were prepared by the high temperature melting method to obtain a strong 2 µm mid-infrared fluorescence emission. The characterization results of the X-ray diffraction (XRD) and differential scanning calorimeter (DSC) show that this glass possesses good crystallization resistance and thermal stability, and its ΔT is 136 °C, which can be successfully drawn. Under the 980 nm LD excitation, strong green (550 nm) and red (660 nm) up-conversion emission were obtained, meanwhile, intensive 2 µm mid-infrared emission was also achieved, and the emission intensity was significantly improved with the increase of Yb3+ concentration, when the Yb3+ content was 2.0, the 2 µm mid-infrared emission intensity was increased by about 28% compared with the content of 0.5, it should be noted that the concentration of Yb3+ is required to be strictly controlled to prevent concentration quenching. In addition, the luminescence process of Ho3+ was further elaborated through the energy transfer mechanism. All results indicate that the Ho3+/Yb3+ co-doped tellurite glass can be an attractive candidate for up-conversion and mid-infrared fiber laser materials. [ABSTRACT FROM AUTHOR]

Under 635 nm laser excitation, the 3.5 μm luminescence, corresponding to the Er3+: 4F 9/2 → 4I 9/2 radiation transition, was demonstrated in Er3+ doped fluoroindate glasses prepared by melt-quenching method. The energy transfer mechanisms were investigated and the 3.5 μm emission intensity reached a maximum for an Er3+ concentration of 9 mol%. The Er3+ energy level lifetimes in fluoroindate glass samples were measured, their oscillator strength parameters were calculated by Judd-Ofelt theory and their emission cross-section at 3.5 μm was obtained. The maximum emission cross-section at 3.51 μm was 4.86 × 10−22 cm2, which indicated that Er3+ doped fluoroindate glass is a potential gain medium for lasing at 3.5 μm. • The absorption coefficient of OH− in galss sample is about 0.0011 cm−1. • The luminescence performance at λ~3.5 μm in Er3+ doped fluoroindate glass samples is investigated. • The maximum emission cross-section of 4.86 × 10−22 cm2 was obtained. [ABSTRACT FROM AUTHOR]

We report a new Dy3+-doped Ga 2 S 3 -Sb 2 S 3 -La 2 S 3 (GSLS) chalcogenide glass for mid-infrared (mid-IR) laser applications. With the addition of La 2 S 3 into the previously studied Ga 2 S 3 -Sb 2 S 3 glass, the thermal stability of the base glass is significantly enhanced. The glass with the composition 20Ga 2 S 3 -75Sb 2 S 3 -5La 2 S 3 (mol.%) shows the best thermal stability for fiber drawing, and the glass can be doped with up to 5 mol.% Dy 2 S 3. The Dy3+-doped GSLS bulk glasses and a multimode fiber exhibit intense emissions at 2.95 μm and 4.40 μm. Spectroscopic analyses show that the mid-IR emissions are with high quantum efficiencies and large stimulated emission cross sections, indicating that Dy3+-doped GSLS glass is a promising candidate for mid-IR fiber laser medium. • A new chalcogenide glass system Ga 2 S 3 -Sb 2 S 3 -La 2 S 3 (GSLS) is developed. • A core/cladding fiber based on Dy3+-doped GSLS glass is fabricated. • The 20Ga 2 S 3 -75Sb 2 S 3 -5La 2 S 3 glass has the best thermal stability. • The Dy3+-doped GSLS glass and fiber show intense mid-infrared emissions. • Fabricated fiber has a background loss of <3 dB/m in the 2–8 μm spectral range. [ABSTRACT FROM AUTHOR]

Broadband mid-infrared luminescence in Dy3+/Er3+ co-doped tellurite glasses was reported in this work. The doped tellurite glasses were prepared using conventional melt-quenching technique, and their structural property and thermal stability were analyzed by the X-ray diffraction (XRD) pattern, Raman spectrum and differential scanning calorimeter (DSC) curve. Judd-Ofelt theory was applied to the absorption spectra to evaluate the spectroscopic properties like radiative transition probability, branching ratio and radiative lifetime of Dy3+ and Er3+ ions. The photoluminescence measured under excitation of 808 nm laser diode (LD) displayed an ultra-broadband mid-infrared band emission with full width at half maximum (FWHM) of ~358 nm in tellurite glass with appropriate amount of Dy3+-Er3+ combination. This broadband mid-infrared band emission located in the range of 2550–3200 nm and originated from the spectral overlapping of 2.85 μm band emission of Dy3+:6H 13/2 → 6H 15/2 transition and 2.7 μm band one of Er3+:4I 11/2 → 4I 13/2 transition. Furthermore, the time resolved fluorescence decay behavior demonstrated the existence of energy transfer between Dy3+ and Er3+ ions which is responsible for the broadband luminescence, and the energy transfer efficiency was estimated. The present results indicate that tellurite glass co-doped with Dy3+-Er3+ ions is promising for applications in mid-infrared band luminescent sources and tunable lasers. • Dy3+/Er3+ co-doped tellurite glass was prepared by melt-quenching method. • An ultra-broadband 2550–3200 nm fluorescence emission with FWHM 358 nm was obtained. • Structural, thermal, spectroscopic properties and luminescent mechanism were investigated. • Dy3+/Er3+ co-doped tellurite glass is promising for MIR broadband tunable lasers. [ABSTRACT FROM AUTHOR]

• Er3+/Ho3+ co-doped tellurite glass was prepared by melt-quenching method. • Co-doping with Ho3+ enhanced the 2.7 µm band intensity of Er3+ by 39%. • ET micro-mechanism for this emission enhancement was quantitatively analyzed. • Er3+/Ho3+ doped tellurite glass with good thermal stability is promising for fiber lasers. Improving the mid-infrared band luminescent intensity in oxide glass system is a serious challenge. In this work, Ho3+ ions was introduced into Er3+ doped tellurite glass, and the improved effect on 2.7 µm band fluorescence of Er3+ was investigated. It was found that when 0.5 mol% of Ho 2 O 3 was incorporated into the tellurite glass with 0.5 mol% of Er 2 O 3 , the 2.7 µm band fluorescence intensity originating from Er3+:4I 11/2 → 4I 13/2 transition increased by about 39% under the excitation of 808 nm laser diode (LD). This significant enhancement was attributed to the energy transfers between Er3+ and Ho3+ ions which improved the population inversion ratio of this emission transition. Analyses of the intensity variations of visible and infrared band emissions as well as the fluorescence decay behavior of Er3+ ions with Ho3+ doped concentration demonstrated the existence of energy transfers, and the energy transfer mechanism was investigated by calculating the relevant micro-parameters to better clarify the origin of fluorescence enhancement. Additionally, Judd-Ofelt theory was applied to the absorption spectrum and the potential spectroscopic properties of Er3+ were evaluated, while DSC curves revealed the good thermal stability of the studied tellurite glass. All these indicated that Er3+/Ho3+ co-doped tellurite glass with appropriate concentrations is a promising candidate applied for 2.7 µm band optoelectronic devices. [ABSTRACT FROM AUTHOR]

Saharan silver ants can inhabit one of the hottest areas, the Sahara Desert, which benefits from their thermoregulatory functionality, thanks to a sophisticated photonic structure of hairs. Mimicking the photonic structure, we fabricated the flexible hair-like photonic structures on polydimethylsiloxane (PDMS). Attaching them to glass bottles for a proof-of-concept demonstration, the considerably enhanced optical reflection was observed as well as the slightly improved mid-infrared emission. These extraordinary properties enabled the temperature of the glass bottles to be reduced by around 5.6 °C in the hot daytime and keep relatively warm in the cold nighttime. On the basis of optical and thermal properties of the silver ants-inspired photonic structures, potential applications could be further found in wearable devices and personal thermal management. • We mimicked the Saharan silver ants' hair and fabricated the biomimetic structures. • The biomimetic structures exhibited the improved optical reflection and heat dissipation as silver ants. • The temperatures of glass bottles, covered by the biomimetic structures, were reduced by 5.6 °C in the hot daytime. • The glass bottles did not exhibit the considerable heat loss in the cold nighttime. • The flexible biomimetic structures could be applied in wearable devices and personal thermal management. [ABSTRACT FROM AUTHOR]

Although amino acids are insensitive to visible light, as is generally accepted, we show that particular light-matter interaction can break this obviousness. Using sensitive (FT-IR)-technique in a combination of a broadband visible light source, we registered emission spectra of glycine in the range 2500-500 cm -1 . Sensitivity of the infrared emission spectrum to the exciting power -induced changes in the glycine structure was demonstrated experimentally.Vibrational spectra of glycine displayed the prominent spectral features of CH 2 , COO-, COOH, NH + 3 groups in the "fingerprint region". Simultaneous appearance of ionised COO- and unionised COOH forms of glycine in solution at neutral pH clearly indicated that visible light induces the partial protonation of COO- groups; if so, visible light irradiation should lead to occurrence of dimers or dimeric hydrogen - bonded structures. Spectroscopic and microscopic evidence of visible light-mediated formation of aggregates and nucleus in aqueous solution was presented.Electronic absorption/emission spectra of glycine in aqueous solution were primarily characterized in the near ultraviolet-visible region (240-600 nm). Negligible absorption near 270 nm was observed for a 1.0 M solution and dramatically enhanced with its "aging". Moreover, an extension of the absorption edge into the region above 400 nm could be seen. Due to the visible light irradiation, we observed modification of electronic structure or occurrence of additional species causing changes in absorption of glycine amino acid. For "aged" solution, it was shown that excitation spectra corresponding to the different emission wavelengths were entirely different, at that each excitation-spectral band had a characteristic emission band.Communicated by Ramaswamy H. Sarma.

Transparent Er3+/Yb3+ co-doped zirconium fluoride-chloride (ZFC) glass are firstly prepared for mid-infrared emission. The stronger 2750 nm emission from Er3+: ZFC glass is owing to a stronger covalence and local asymmetry of the crystal field around the Er3+ ions. The low phonon energy (600 cm−1) of ZFC glass are calculated from FTIR spectra and confirmed by Raman spectra. The low OH− concentration (9.75 × 10−17 cm−3) and high transmittance (1300-4000 cm−1) of ZFC glass are beneficial to mid-infrared emission. Co-doping rare earth ions Yb3+ enhances the 2750 nm emission. The energy transfer process between Yb3+ and Er3+ are identified based on luminescence spectra and decay curves. The role of Yb3+ plays the sensitizer on Er3+: 4I 11/2 and enhances the excited state absorption of Er3+: 4I 13/2 → 4F 9/2 , which is good for transition Er3+: 4I 11/2 → 4F 13/2. Thus, Er3+/Yb3+: ZFC glass with large emission cross section (1.06 × 10−20 cm2) is a potential laser application material. • The Er3+/Yb3+ co-doped zirconium fluoride-chloride glass is firstly prepared for 2.7 μm emission. • The transparent glass possess low OH– content (9.75 × 1017 cm–3). • The lifetime of Er3+: 4I 11/2 is as long as 3.05 ms. • The emission cross section around 2.7 μm emission is up to 1.06×10–20 cm2. [ABSTRACT FROM AUTHOR]

Ho3+/Yb3+ co-doped tellurite-germanate glasses with lower phonon energy (779 cm−1) and higher thermal stability were prepared by conventional melt quenching. The mid-infrared fluorescence spectra of the prepared glasses were investigated by 980 nm laser pumping. The full width at half maximum (FWHM) and lifetime of the sample at 2.0 μm were 186 nm and 8.09 ms, respectively. Compared with the reported glasses for this type, these values were effectively improved. In particular, the FWHM and emission lifetime of the prepared glass at 4.1 μm reached 276 nm and 8.17 ms, respectively, which have not been reported yet. Meanwhile, compared to the recently reported tellurite glasses, the ΔT was increased by approximate 22.7%. Strong up-conversion visible emission peaks at 547, 662, and 756 nm and near-infrared emission at 1.20 μm were observed in Ho3+/Yb3+ co-doped glass. Meanwhile, photoluminescence measurements showed that the doping of the appropriate amount of Yb3+ ions significantly enhanced the emission intensity of the samples at 2.0 μm and 4.1 μm. Therefore, the Ho3+/Yb3+ co-doped tellurite-germanate glass is a promising candidate for mid-infrared fiber and laser materials applications. • Ho3+/Yb3+ co-doped tellurite-tellurite glass has a lower phonon energy (779 cm−1). • Ho3+/Yb3+ co-doped tellurite-tellurite glass has a larger ΔT (200 °C). • The full width at half maximum (FWHM) of the sample at 4.1 μm reached 276 nm. • The emission lifetime of the prepared glass at 4.1 μm reached 8.17 ms • The FWHM and lifetime of the sample at 2.0 μm were 186 nm and 8.09 ms, respectively. [ABSTRACT FROM AUTHOR]

The ~3 μm fluorescence was investigated in the Ho 2 O 3 -doped transparent tellurite glass-ceramic for the first time. The branching-ratios and emission cross-sections were calculated. The glass-ceramics had high branching-ratio (20.5%) and large emission cross-section (1.76 × 10−20 cm2) corresponding to Ho3+:5I 6 →5I 7 transition. After crystallization, the ~3 μm fluorescence intensity increased obviously excited by 640 nm laser diode. The broadband fluorescence about 3 μm was observed under excitation by a 1950-nm thulium-doped fiber lasers. The increased ~3 μm fluorescence intensity and narrowed spectrum demonstrated the Ho3+ ions embedded into the crystalline phase. These results indicate that the tellurite glass-ceramics may be a promising material for mid-infrared lasers. • ~3 μm emission of Ho3+ doped tellurite GC was studied for the first time. • The emission cross section for 3 μm emission in GCH reached to 1.76 × 10−20 cm2. • Excited by 1950 nm thulium-doped fiber lasers, the 3 μm emisson were observed. • The emission intensity of GCH in the range of 2700–2760 nm increased nine times. • The ~3 μm emission spectrum in GCH narrowed obviously. [ABSTRACT FROM AUTHOR]

Bismuth-germanate glasses with low hydroxide content co-doped with Ho3+/Yb3+ ions have been investigated in terms of structural and spectroscopic properties. To reduce OH- ions content and improve transmittance value at the wavelength of 3.1 µm, the glass synthesis has been carried out in low vacuum conditions (45–65 mBar). The composition of the host glass based on heavy metal oxides affects the maximum phonon energy (hωmax = 724 cm−1), which low value has a positive impact on the mid-infrared emission parameters. Emission band at the wavelength of 2.87 µm was observed in glass co-doped with mol% 0.25 Ho2O3/0.75 Yb2O3 under 980 nm high power laser diode wavelength excitation. Lifetime measurements of the Yb3+:2F5/2 quantum level indicate efficient Yb3+ → Ho3+ energy transfer (η = 61%). The developed active bismuth-germanate glass was used as the core of optical fibre operating in the mid-infrared region. [ABSTRACT FROM AUTHOR]