Mechanism of Photoluminescence in Erbium-Doped Chalcogenide

The monograph describes the technique of the synthesis of glasses and the method of the growth of erbium-doped single crystals. The photoluminescence spectra of Ag0.05Ga0.05Ge0.95S2-Er2S3 glasses and glasses from the Ga2S3-La2S3-Er2S3 system have been investigated in the visible and near-infrared ranges. According to the energy transitions in the erbium ions, a radiation mechanism for conversion and up-conversion luminescence has been established. The role of structural ordering and the influence of defects on the radiation efficiency of Er3+ ions have been investigated. The spectra of photoluminescence of (Ga54.59In44.66Er0.75)2S300 and (Ga69.75La29.75Er0.5)2S300 single crystals have been studied. The efficiency of the radiation of the amorphous and crystalline materials has been compared. Also, the temperature dependence of the integral intensity of the radiation of glasses and single crystals has been studied. It is established that in a limited temperature range, these materials can be used for the manufacture of non-contact optical thermosensors

CdS(Se) and PbS(Se) Quantum Dots with High Room Temperature Quantum Efficiency in the Fluorine-Phosphate Glasses

In this study, the luminescent properties of the CdS(Se) quantum dots (QDs) with the mean size of 2–4 nm, the (PbS)n/(PbSe)n molecular clusters (MCs) and PbS(Se) quantum dots (QDs) with the mean size of 2–5 nm embedded in the fluorine-phosphate glass are investigated. The dependence of the photo luminescence absolute quantum yield (PL AQY) on the sizes of the CdS(Se) QDs are studied. It is found that the PL AQY of the CdSe QDs increases monotonically to its maximum height and then falls down. The PL AQY of the CdS(Se) QDs can reach 50–65%. Luminescence of (PbS)n/(PbSe)n MCs embedded in fluorine-phosphate matrix and excited by UV radiation is obtained in the visible spectral region and its absolute quantum yield was up to 10%. The PbSe QDs have broadband photoluminescence with quantum efficiency about five times more than MCs (~50%) in the spectral range of 1–1.7 µm. Glasses doped with PbS(Se) QDs provide potential application as infrared fluorophores, which are both efficient and possess short life times. The glass matrix protects the QDs from external influence and their optical properties remain unchanged for a long time

The role of glass modifiers in the solubility of Tm3+ ions in As2S3 glasses

Au cours des années une variété des compositions de verre chalcogénure a été étudiée en tant qu’une matrice hôte pour les ions Terres Rares (TR). Pourtant, l’obtention d’une matrice de verre avec une haute solubilité des ions TR et la fabrication d’une fibre chalcogénure dopée au TR avec une bonne qualité optique reste toujours un grand défi. La présente thèse de doctorat se concentre sur l'étude de nouveaux systèmes vitreux comme des matrices hôtes pour le dopage des ions TR, ce qui a permis d'obtenir des fibres optiques dopées au TR qui sont transparents dans l’IR proche et moyenne. Les systèmes vitreux étudiés ont été basés sur le verre de sulfure d'arsenic (As2S3) co-dopé aux ions de Tm3+ et aux différents modificateurs du verre. Premièrement, l'addition de Gallium (Ga), comme un co-dopant, a été examinée et son influence sur les propriétés d'émission des ions de Tm a été explorée. Avec l'incorporation de Ga, la matrice d’As2S3 dopée au Tm a montré trois bandes d'émission à 1.2 μm (1H5→3H6), 1.4 μm (3H4→3F4) et 1.8 μm (3F4→3H6), sous l’excitation des longueurs d'onde de 698 nm et 800 nm. Les concentrations de Tm et de Ga ont été optimisées afin d’obtenir le meilleur rendement possible de photoluminescence. À partir de la composition optimale, la fibre Ga-As-S dopée au Tm3+ a été étirée et ses propriétés de luminescence ont été étudiées. Un mécanisme de formation structurale a été proposé pour ce système vitreux par la caractérisation structurale des verres Ga-As-S dopés au Tm3+, en utilisant la spectroscopie Raman et l’analyse de spectrométrie d'absorption des rayons X (EXAFS) à seuil K d’As, seuil K de Ga et seuil L3 de Tm et il a été corrélé avec les caractéristiques de luminescence de Tm. Dans la deuxième partie, la modification des verres As2S3 dopés au Tm3+, avec l'incorporation d'halogénures (Iode (I2)), a été étudiée en tant qu’une méthode pour l’adaptation des paramètres du procédé de purification afin d’obtenir une matrice de verre de haute pureté par distillation chimique. Les trois bandes d'émission susmentionnées ont été aussi bien observées pour ce système sous l'excitation à 800 nm. Les propriétés optiques, thermiques et structurelles de ces systèmes vitreux ont été caractérisées expérimentalement en fonction de la concentration d’I2 et de Tm dans le verre, où l'attention a été concentrée sur deux aspects principaux: l'influence de la concentration d’I2 sur l'intensité d'émission de Tm et les mécanismes responsables pour l'augmentation de la solubilité des ions de Tm dans la matrice d’As2S3 avec l’addition I2.Over the years a number of chalcogenide glass compositions have been studied as host matrices for Rare Earth (RE) ions. However, it still remains a great challenge to obtain a glass matrix with high solubility of RE ions and to fabricate a RE doped chalcogenide glass fiber with good optical quality. The present PhD thesis focuses on the study of new glassy systems as host matrices for doping of RE ions, which allowed to obtain RE doped optical fibers transparent in near and middle IR. Studied glassy systems were based on well-known arsenic sulphide (As2S3) glasses co-doped with Tm3+ ions and different glass modifiers. Firstly, the addition of Gallium (Ga) ions as co-dopants was examined and their influence on the emission properties of Tm ions was explored. With the incorporation of Ga into the host, Tm doped As2S3 glasses display three strong emission bands at 1.2 μm (1H5→3H6), 1.4 μm (3H4→3F4) and 1.8 μm (3F4→3H6) under excitation wavelengths of 698 nm and 800 nm. Despite the very small glass forming region of the system Ga-As-S we could optimise the concentration ratio of Ga and Tm to achieve the highest possible photoluminescence efficiency. From the optimal composition, Tm3+ doped Ga-As-S fiber was drawn and its luminescence properties were studied. Through structural characterisation of Tm doped Ga-As-S glasses, using Raman spectroscopy and Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy at As K-edge, Ga K-edge and Tm L3-edge, a formation mechanism has been proposed for this glassy system and it was correlated with luminescence features of Tm ions. In the second part, the modification of Tm3+ doped As2S3 glasses with the incorporation of halides (namely Iodine (I2)) was investigated, as a method for tailoring the process parameters for purification, in order to obtain a high purity glass matrix via chemical distillation. All three of above mentioned emission bands were observed for this system as well, under the 800 nm of excitation wavelength. Optical, thermal and structural properties of these glassy systems were characterized experimentally depending on the concentration of I2 and Tm in the glass, where the attention was concentrated on two principal aspects: the influence of the concentration of I2 on the intensity of emission of Tm and the mechanisms responsible for the increase of the solubility of Tm ions in As2S3 glass matrix with addition of I2

Nanoparticles in Solution-Derived Chalcogenide Glass Films

The results in this thesis are from our efforts to modify the optical properties of solution-derived chalcogenide glass films by the incorporation of nanomaterials. First, the composition Ge23Sb7S70 was selected as the appropriate glass matrix for testing because solution-derived films of this composition have been well-studied in our group. Additionally, this composition was found to be less sensitive to certain processing parameters than As2S3, another well-studied, candidate chalcogenide glass composition, making Ge23Sb7S70 more suitable for the addition of nanomaterials. Optimization of film process parameters was performed to obtain high-quality films appropriate for doping with nanomaterials. This consisted of determining the maximum solubility of glass in propylamine solvent to obtain films of adequate thickness, as well as optimizing the water content in the propylamine to minimize surface roughness and cracking. Two classes of nanomaterials were used to investigate the principles of doped films, spherical metallic nanoparticles (MNPs), and spherical semiconductor nanoparticles, also known as quantum dots (QDs). Gold was the particular type of MNP used, and is characterized by its surface plasmon resonance (SPR) absorption band, which is tunable and environment sensitive, and leads to interesting properties such as magneto-optic effects. Two types of QDs were used, CdSe and PbS. QDs are widely known for their high photostability and luminescence, which is tunable by varying the size of the QD. CdSe exhibits luminescence in the visible spectral region, while PbS emits in the near-infrared (NIR). With Au nanoparticles, experiments were performed to determine the maximum nanoparticle concentration in the glass solution by utilizing UV-vis-NIR spectroscopy. Films were then deposited and characterized by their absorption spectra. In the case of QDs, solutions were not stable for long enough periods of time, so only the films deposited from the solutions could be analyzed. UV-vis-NIR spectroscopy and photoluminescence measurements were used to observe the intensity and location of the characteristic absorption and luminescence bands of the QDs. Quantum yield and luminescence lifetime were used to quantitatively characterize the behavior of the QDs in different environments when possible. Different organic ligands on the surface of the QDs were tested and compared to evaluate their effect on the behavior of the QD. The results show that small amounts of Au MNPs can be dispersed in a chalcogenide glass solution with minimal aggregation, as quantified by the absorption spectra. Comparison of the optical behavior of the films to that of the solutions showed that the concentration of Au MNPs was too low to observe the characteristic SPR band. The results of the QD testing show that luminescence can be observed from a deposited film, and that the behavior of the QDs, characterized by quantum yield and lifetime, varies greatly in different environments. Furthermore, it was found that different capping agents led to different behavior of the QDs in the glass solution, affecting the properties of the deposited film

Glassy Materials Based Microdevices

Microtechnology has changed our world since the last century, when silicon microelectronics revolutionized sensor, control and communication areas, with applications extending from domotics to automotive, and from security to biomedicine. The present century, however, is also seeing an accelerating pace of innovation in glassy materials; as an example, glass-ceramics, which successfully combine the properties of an amorphous matrix with those of micro- or nano-crystals, offer a very high flexibility of design to chemists, physicists and engineers, who can conceive and implement advanced microdevices. In a very similar way, the synthesis of glassy polymers in a very wide range of chemical structures offers unprecedented potential of applications. The contemporary availability of microfabrication technologies, such as direct laser writing or 3D printing, which add to the most common processes (deposition, lithography and etching), facilitates the development of novel or advanced microdevices based on glassy materials. Biochemical and biomedical sensors, especially with the lab-on-a-chip target, are one of the most evident proofs of the success of this material platform. Other applications have also emerged in environment, food, and chemical industries. The present Special Issue of Micromachines aims at reviewing the current state-of-the-art and presenting perspectives of further development. Contributions related to the technologies, glassy materials, design and fabrication processes, characterization, and, eventually, applications are welcome

Engineering of Glasses for Advanced Optical Fiber Applications

Advanced optical applications (such as fiber optics)demand the engineering of innovative materialswhich provide the requisite optical performance in aform with specific functionality necessary for thedesired application. We will report on recent effortsto engineer new non-oxide glasses with tailoredphoto-sensitive response, and multi-component oxideglasses optimized for use in next generation Ramanamplification applications. The ultimate performanceof such glasses relies on control of the formation andstability of defective and/or metastable structuralconfigurations and their impact on physical as well aslinear and nonlinear optical properties. Direct laserwriting has drawn considerable attention since thedevelopment of femtosecond lasers and therecognition that such systems possess the requisiteintensity to modify, reversibly or irreversibly thephysical properties of optical materials. Such“structuring” has emerged as one of several possibleroutes for the fabrication of waveguides and otherphoto-induced structures

Rare-earth ion doped chalcogenide waveguide amplifiers

Chalcogenide glass waveguide devices have received a great deal of attention worldwide in the last few years on account of their excellent properties and potential applications in mid-infrared (MIR) sensing and all-optical signal processing. Waveguide propagation losses, however, currently limit the potential for low power nonlinear optical processing, and the lack of suitable on chip integrated MIR sources is one of the major barriers to integrated optics based MIR sensing. One approach to overcome the losses is to employ rare-earth ion doped waveguides in which the optical gain can compensate the loss, in such a way that the conversion efficiency of nonlinear effects is increased significantly. For infrared applications, the long wavelengths potentially attainable from rare-earth ion transitions in chalcogenide hosts are unique amongst glass hosts. New rare-earth ion doped chalcogenide sources in the MIR range could benefit molecular sensing, medical laser surgery, defence etc. Despite these promising applications, until now, no one has succeeded in fabricating rare-earth ion doped chalcogenide amplifiers or lasers in planar devices. This work develops high quality erbium ion doped chalcogenide waveguides for amplifier and laser applications. Erbium ion doped As2S3 films were fabricated using co-thermal evaporation. Planar waveguides with 0.35 dB/cm propagation loss were patterned using photolithography and plasma etching on an erbium ion doped As2S3 film with an optimised erbium ion concentration of 0.45x1020 ions/cm3. The first demonstration of internal gain in an erbium ion doped As2S3 planar waveguide was performed using these waveguides. With different film deposition approaches, promising results on intrinsic lifetime of the Er3+ 4I13/2 state were achieved in both ErCl3 doped As2S3 films (2.6 ms) and radio frenquency sputtered Er3+:As2S3 films (2.1 ms), however, no waveguide was fabricated on these films due to film quality issues and photopumped water absorption issues. The low rare-earth ion solubility of As2S3 is considered the main factor limiting its performance as a host. Gallium-containing chalcogenide glasses are known to have good rare-earth ion solubility. Therefore, a new glass host material, the Ge-Ga-Se system, was investigated. Emission properties of the bulk glasses were studied as a function of erbium ion doping. A region between approximately 0.5 and 0.8 at% of Er3+ ion was shown to provide sufficient doping, good photoluminescence and adequate lifetime to envisage practical planar waveguide amplifier devices. Ridge waveguides based on high quality erbium ion doped Ge-Ga-Se films were patterned. Significant signal enhancement at 1540 nm was observed and 50 % erbium ion population inversion was obtained, in waveguides with Er3+ concentration of 1.5x1020 ion/cm3. To the Author's knowledge, this is the highest level of inversion ever demonstrated for erbium ions in a chalcogenide glass host and is an important step towards future devices operating at 1550 nm and on the MIR transitions of erbium ions in chalcogenide glass hosts. Photoinduced absorption loss caused by upconversion products in the waveguides is the remaining hurdle to achieving net gain. Further research is needed to find suitable compositions that possess high rare-earth ion solubility whilst avoiding the detrimental photoinduced losses

Optical Characterization of Rare Earth Doped Glasses

Optical amplifiers are highly sought-after in optical communications to power boost light signals carrying information. Rare Earth doped glasses have been the medium of choice for optical amplification. It is, therefore, essential to understand the interaction of light with potential host glasses for rare-earths before they could be proposed as suitable candidates. In this research, we have optically characterized three different rare earth doped bulk glasses. The glass samples investigated were Neodymium doped Gallium Lanthanum Sulfide (GLS:Nd), Erbium doped Germanium Gallium Sulfide (GeGaS:Er) and Erbium doped Fluorochlorozirconate (FCZ:Er). The transmission spectra, T(λ), was used in identifying the absorption transitions of rare earth ions from the ground level to the various excited levels and in obtaining the optical absorption coefficient, α(λ). This in turn was used in determining the Judd-Ofelt parameters, which were then used in obtaining radiative lifetimes of the energy levels of interest. Photoluminescence emission bands were also identified and their shapes were investigated. Finally, a comparison of the Judd-Ofelt lifetime with the experimental decay time was also done. From which, the major decay mechanism of the rare earth ions from the energy level under investigation was concluded

Photonic devices for integrated optical applications

work presented in this thesis encompasses an investigation into the use of ultrafast laser inscription in the fabrication of glass based photonic devices for integrated optical applications. Waveguide fabrication and characterisation experiments were carried out in three categories of glass substrate. Firstly, waveguides were inscribed in an erbium doped glass with the aim of fabricating optical amplifiers and lasers operating in the 1.5 μm spectral region. Low loss waveguides were fabricated in substrates with different dopant concentrations. Fibre to fibre net gain was achieved from one substrate composition, however it was found that ion clustering limited the amount of achievable gain. Laser action was demonstrated by constructing an optical fibre based cavity around the erbium doped waveguide amplifier. Waveguides were also inscribed in bismuth doped glass with the aim of fabricating optical amplifiers and lasers operating in the 1.3 μm spectral region. Low loss waveguides were fabricated, however the initial composition was incapable of providing gain. A proven substrate material was employed, demonstrating ultra-broadband gain spanning more than 250 nm. High losses prevented the achievement of net gain, however the broad potential of the substrate material was highlighted. Finally, waveguides were inscribed in a Chalcogenide glass. Strong refractive index contrasts were observed, with a wide range of waveguiding structures produced. Supercontinuum experiments were carried out in order to confirm the nonlinear behaviour of the waveguides. A spectrally smooth supercontinuum spanning 600 nm was generated, providing a potentially useful source for optical coherence tomography