Rare-earth Doped Chalcogenide Research Articles

Solution-processed Er3+-Doped GeS2 chalcogenide glass films with NIR photoluminescence towards functional flexibility and integration.

Rare-earth doped chalcogenide films are major components in flexible and integrated photonic and optoelectronic devices for modern communication systems, metrology, and optical sensing. However, it is still challenging to develop a high concentration of rare-earth doping chalcogenide film with a smooth surface to realize efficient photoluminescence (PL). Here, we demonstrate that Er3+-doped GeS2 films are prepared by spin-coating based on a two-step dissolution process. Such a two-step process provides the high solubility of Er3+ in GeS2 films and exhibits efficient emission at ∼1.5 µm crossing the telecommunication C-band. The highest PL emission intensity is obtained in GeS2 films doped with 1.4 mol% of Er3+, and this PL in GeS2 films is reported for the first time. We propose adjustments of annealing parameters for improving the PL characteristics in such materials. Through the control precision of the heating rate and annealing temperature, the smooth surface of GeS2 films enables efficient photo-luminescence. This two-step dissolution-based strategy would pave a new path to design luminescent chalcogenide films for application in flexible and integrated optoelectronics and photonics.

Photoluminescent Er-doped As20Se80 thin films and channel waveguides produced by thermal reflow

The chalcogenide glasses are an excellent material alternative for the poorly developed optics of the mid-infrared region on integrated photonics. Their great transmission in the IR region, the outstanding non-linear optical properties, and the recently explored possibility of processing by thermal reflow have sparked considerable interest in the fabrication of micro and nano-structures with symmetric and smooth surfaces suitable for optical components. The thermal reflow nevertheless is not useful for certain glass compositions since it induces phase separation and crystallization that compromise the optical quality. Rare earth-doped chalcogenides, of great interest for the development of laser and amplifiers, are especially prone to such dehomogenization since they have shown to be difficult to synthesize and process without obtaining fluorescence quenching caused by agglomeration and phase separation. In this work, we demonstrate for the first time that under certain conditions it is possible to induce thermal reflow in Er-doped chalcogenide thin films without inducing agglomeration and extinguishing the erbium emission. The films, produced by the co-evaporation of metallic erbium and As20Se80 glass matrix, demonstrated great molecular flexibility that allows to observe thermal reflow in films with erbium concentrations up to 0.6 at%. We use this thermal reflow in doped ridge channel waveguides (produced by photolithography) to reduce the optical losses and to enhance the fluorescence properties of the material by the rearrangement of the emitting ions. Our study opens the door for the fabrication and processing of rare earth-doped chalcogenide planar devices and their future integration into photonic circuits.

Photo-Writable Sulfide Glasses Used to Fabricate Core-Clad Fiber Doped with Pr3+ for Mid-IR Luminescence

With the ultimate goal of developing rare-earth doped chalcogenide fiber fabrication for sensing, amplification, and laser applications, a core/clad germanium-gallium sulfide fiber doped with Pr3+ has been fabricated. The compositions of the core and the clad were selected to ensure the positive ∆n by adding CdI2 and CsCl, respectively, in the GeS2-Ga2S3 matrix. The choice of these compositions was also justified from experimental parameters, including characteristic temperatures and viscosity. Moreover, the permanent photo writability of the sulfide glass family by a femtosecond laser is investigated from the perspective of Bragg grating photo-inscription. Structural investigations by Raman spectroscopy are presented and the effect of the Pr3+ rare-earth ion on the structure is underlined. Finally, the emission of the step-index fiber, made by the rod-in-tube technique between 3.1 µm and 5.5 µm (by pumping at 1.55 µm), is demonstrated.

Role of rare earth on the spectral properties of chalcogenide glassy alloys: A review

In this paper, recent results regarding rare earth element doped with chalcogenide glasses for optical gain media such as amplifiers and lasers are reviewed. Rare earth Chalcogenide glasses are formed when chalcogen elements (S, Se, Te etc.) are mixed with new additive elements (Ge, Ga, Sb, As etc.) and also with rare earth elements (Er, Dy, Pd, Pr etc.) from periodic table and prepared by melt quench technique (MQT). Rare earth element doped with chalcogenide glasses has been emerged as a suitable candidate for applications in the numeral passive and active. Among various materials, chalcogenide glasses show significant improvement in their emission properties in the optical communication range and spectroscopic properties. Finally, rare earth doped chalcogenide and optical fibers show potential for high power mid-infrared gain medium and their spectroscopic properties as well.

Comparative study of Er3+-doped Ga-Ge-Sb-S thin films fabricated by sputtering and pulsed laser deposition

Despite the renewed interest in rare earth-doped chalcogenide glasses lying mainly in mid-infrared applications, a few comprehensive studies so far have presented the photoluminescence of amorphous chalcogenide films from visible to mid-infrared. This work reports the fabrication of luminescent quaternary sulfide thin films using radio-frequency sputtering and pulsed laser deposition, and the characterization of their chemical composition, morphology, structure, refractive index and Er3+ photoluminescence. The study of Er3+ 4I13/2 level lifetimes enables developing suitable deposition parameters; the dependency of composition, structural and spectroscopic properties on deposition parameters provides a way to tailor the RE-doped thin film properties. The surface roughness is very low for both deposition methods, ensuring reasonable propagation optical losses. The effects of annealing on the sulfide films spectroscopy and lifetimes were assessed. PLD appears consistent composition-wise, and largely independent of the deposition conditions, but radiofrequency magnetron sputtering seems to be more versatile, as one may tailor the film properties through deposition parameters manipulation. The luminescence via rare earth-doped chalcogenide waveguiding micro-structures might find easy-to-use applications concerning telecommunications or on-chip optical sensors for which luminescent sources or amplifiers operating at different wavelengths are required.

Simulation of Multilayered Heterojunction-Based Chalcogenide Fiber SPR Sensor With Ultrahigh Figure of Merit in Near Infrared

The dynamic nature of radiation damping in plasmonic structures can have immense potential in relation to significant improvement in plasmonic sensor performance. In this paper, we have explored the careful tuning of dynamic radiation damping in Si-Ag-graphene-Al2O3 heterojunction-based fiber optic plasmonic sensor structure. Low-refractive index rare-earth doped chalcogenide glass is considered as fiber material in near infrared spectral region. The simultaneous tuning of Ag and Al2O3 layer thicknesses with wavelength in appropriate broad ranges is investigated to enhance the sensor’s performance as much as possible. As another interesting step, the presence/absence of graphene layer on sensor’s performance is also examined. The results indicate that significantly large figure of merit (FOM) of magnitude 19212.67 RIU $^{-1}$ at $\lambda = 969$ nm for 5.2-nm-thick Al2O3 layer, and 36.6-nm-thick Ag layer is achievable from the proposed sensor with graphene. The above FOM is substantially larger than the existing (reported) plasmonic sensors claiming large FOM values. The findings of this paper can be crucial for developing surface plasmon reasonance biosensors with highly enhanced performance.

Enhancing extraction efficiency of mid-infrared fluorescence in chalcogenide glass via photonic crystal

The use of rare earth-doped chalcogenide glass is an attractive method to develop mid-infrared sources. In this work, Er3+-doped chalcogenide glass is prepared, and photonic crystal (PC) pattern is designed to improve the extraction efficiency of light emission from the sample surface. The finite difference time domain simulation shows that the light extraction efficiency from the sample surface can be 1.62 times stronger than that from the sample without PC structure by introducing a simple two-dimensional (2D) PC structure into glass samples. This improvement was the result of the efficient light diffraction on the surface because of the integrated 2D PC. Results in this work offer a potential in developing midinfrared light sources.

Laser desorption ionization time-of-flight mass spectrometry of erbium-doped Ga-Ge-Sb-S glasses.

Rare earth-doped sulphide glasses in the Ga-Ge-Sb-S system present radiative emissions from the visible to the middle infrared range (mid-IR) range, which are of interest for a variety of applications including (bio)-chemical optical sensing, light detection, and military counter-measures. The aim of this work was to reveal structural motifs present during the fabrication of thin films by plasma deposition techniques as such knowledge is important for the optimization of thin film growth. The formation of clusters in plasma plume from different concentrations of erbium-doped Ga5Ge20Sb10S65 glasses (0.05, 0.1, and 0.5 wt. % of erbium) using laser (337 nm) desorption ionization (LDI) was studied by time-of-flight mass spectrometry (TOF MS) in both positive and negative ion mode. The stoichiometry of the Ga(m)Ge(n)Sb(o)S(p)(+/-) clusters was determined via isotopic envelope analysis and computer modelling. Several Ga(m)Ge(n)Sb(o)S(p)(+/-) singly charged clusters were found but, surprisingly, only four species (Sb3S4(+/-), GaSb2S(p)(+/-) (p = 4, 5), Ga3Sb2S7(+/-) ) were common to both ion modes. For the first time, species containing rare earths (GaSb2SEr(+) and GaS6 Er2(+)) were identified in the plasma formed from rare earth-doped chalcogenide glasses, directly confirming the importance of gallium presence for rare earth bonding within the glassy matrix. The local structure of Ga-Ge-Sb-S glasses is at least partly different from the structure of species identified in plasma by mass spectrometry, as deduced from Raman scattering spectroscopy analysis; these glasses are mainly formed by [GeS4/2]/[GaS4/2] tetrahedra and [SbS3/2] pyramids. Extended X-ray absorption fine structure measurements show that Er(3+) ions in Ga-Ge-Sb-S glasses are surrounded by 7 sulphur atoms.

Spectroscopic properties of Ni 2+ and rare-earth codoped Ge–Ga–Sb–S glass

The infrared emission properties of rare-earth (i.e., Dy 3+, Pr 3+ or Sm 3+) and nickel-codoped Ge–Ga–Sb–S glasses were investigated by photoluminescence measurements. It was found that the emission intensities of the rare-earth doped glasses were significantly weakened even with very few amount of nickel (i.e., 500 at. ppm). On the other hand, the nickel-doped glasses show larger indices of refraction, which property will be desirable in nonlinear optics. Our results, however, suggest that to obtain rare-earth doped chalcogenide glasses of better infrared emission property it is necessary to keep the nickel dopant as low as possible.

Rare-earth doped chalcogenide thin films fabricated by pulsed laser deposition

Erbium doped Ge–Ga–Se thin films were fabricated by the pulsed laser deposition (PLD) technique in vacuum using a KrF pulse laser with λ = 248 nm, and a pulse duration of 15 ns. The films were fabricated at room temperature onto glass substrates. The morphological, optical and thermal properties of the films showed good optical and thermal stability. The mechanical properties including film adhesion are relatively poor for thicker films and the microstructure reveals the presence of droplets. Annealing in vacuum improved the film adhesion and substantially enhanced the efficiency of photoluminescence.

Effects of carbon, hydrocarbon and hydroxide impurities on praseodymium doped arsenic sulfide based glasses

In rare earth doped chalcogenide glasses, hydrocarbon and hydroxyl based impurities affect the absorption and fluorescence properties. Corresponding to Fourier transform infrared spectroscopy (FTIR) investigations sulfur is the main source of these impurities. The simultaneous occurrence of H, O, C impurities leads to an interaction influenced by the preparation conditions. Under melting conditions of arsenic sulfide and germanium/gallium doped arsenic sulfide (900°C, evacuated sealed quartz glass ampoules) hydrocarbon species tend to react with oxide impurities (As 2O 3, GeO 2) and hydroxyl with carbon oxysulfide and carbon dioxide. Excess of carbon appears as carbon disulfide (CS 2) in the FTIR spectra. The specific absorption coefficient of CS 2 is found to be 0.012±0.003 cm −1/ wt.ppm . Hydrocarbon impurities additionally increase the hydrosulfide content of samples. Based on the FTIR investigationes the specific absorption coefficient of the alkane C 24H 50 is estimated to be 0.006±0.001 cm −1/ wt.ppm . The `oxygen trap process' of carbon and hydrocarbon components in chalcogenide glasses is confirmed by thermodynamic calculations. The defined adjustment of hydrosulfide (500–1000 wt.ppm) and hydroxyl content (less 3 wt.ppm) of the As–Ge–Ga–S glass by carbon/hydrocarbon doping allowed us to prepare optimised fibers with attenuation 1.5–2 dB m −1 and a sufficient lifetime of the excited level 1 G 4 220–180 μs at 750 wt.ppm Pr 3+. The glass is introduced as core material in a single mode fiber for 1.3 μm amplification.

Mid-wave IR and long-wave IR laser potential of rare-earth doped chalcogenide glass fiber

The mid-wave IR and long-wave IR laser potential of rare-earth ions in chalcogenide glass fiber is reviewed. Spectroscopic data for the mid-wave and long-wave IR transitions for Pr/sup 3+/, Dy/sup 3+/, and Tb/sup 3+/ in chalcogenide glass is presented and used as a basis for discussion of laser potential in these glasses.

Photoinduced effects in undoped and rare-earth doped chalcogenide glasses: review

The mechanisms of metastable photoinduced anisotropy and photorefraction in chalcogenide glasses are proposed based on increased polarizability of these materials (increased cubic susceptibility χ (3)). Flexible intrinsic structural units (oppositely charged chalcogen pairs) are suggested to be the origin of photoinduced anisotropy, and account for its re-orientation reversibility. I suggest that inflexible, photo-created, charged cation trapping sites dominate the mechanism of photorefraction. An increase of photoinduced anisotropy in glasses doped with Pr 3+ ions is reported and attributed to Pr 3+-induced increase of polarizability of charged chalcogen pairs, when Pr 3+ ions adhere to the negatively charged component of these pairs. The Boson peak in the Raman spectra of glasses increases with Pr 3+-doping confirming an increase of polarizability of intrinsic structural units into which Pr 3+ ions are incorporated. The Boson peak also increases after prolonged irradiation of chalcogenide glasses with near-gap-light indicating a light-induced creation of bonds with increased polarizability (e.g. broken bonds), which cause photorefraction. Fatigue of host and Pr 3+-dopant photoluminescence in chalcogenide glasses induced by prolonged irradiation with near-gap-light is discussed in correlation with accompanying photorefraction.

Effect of transition metal co-doping on broad band luminescence excitation mechanism in rare earth-doped chalcogenide glasses

Photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopy were carried out on As 12Ge 33Se 55 samples co-doped with Er and different elements of the first transition series to investigate the effect of the transition metals on a previously observed broad excitation band. It was found that Fe, Cu and Mn all decrease the strength of the broad excitation band, while the Cr alters the lineshape by contributing additional oscillator strength at long wavelengths. Low temperature studies reveal that the mechanism leading to the broad band shifts to larger energies, following the bandgap, while the Cr absorption band is insensitive to the bandgap, indicating a different origin for the two excitation mechanisms. PLE spectroscopy of a Dy,Cr co-doped sample confirm the distinction between the two processes. The Cr excitation mechanism is attributed to a d-to-d band absorption followed by non-radiative energy transfer to the Er dopants. A model for the broad PLE band based on strongly lattice coupled impurities is presented.

Rare-earth doped chalcogenide glass fibre laser

We report on the first laser action in a rare-earth doped chalcogenide glass fibre. Laser action at 1080nm was obtained in a 22mm long gallium lanthanum sulphide glass fibre with a neodymium doped core, fabricated by the rod-in-tube technique. The laser was pumped continuous wave with a Ti:sapphire laser at 815nm and showed a self-pulsing behaviour.

Rare-earth doped chalcogenide glass laser

Laser action in a rare-earth doped chalcogenide glass was demonstrated for the first time showing that this class of glasses is suitable for active applications such as optical amplifiers and lasers. The neodymium-doped gallium lanthanum sulphide glass laser operated continuous wave at a wavelength of 1.08 µm when pumped with a Ti:sapphire laser at either 0.815 µm or 0.890 µm.

Broad-band excitation of Pr/sup 3+/ luminescence by localized gap state absorption in Pr:As/sub 12/Ge/sub 33/Se/sub 55/ glass

Photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopy of Pr/sub 2/S/sub 3/-doped As/sub 12/Ge/sub 33/Se/sub 55/ glass have detected two broad peaks in the PL spectrum, centered at /spl sim/1340 nn and /spl sim/1620 nm, characteristic of the /sup 1/G/sub 4//spl rarr//sup 3/H/sub 5/ and /sup 3/F/sub 3//spl rarr//sup 3/H/sub 4/ transitions, respectively. The 1620-nm band exhibits a strong, broad, below-gap PLE band extending from 500 nm to 1000 nm, which is nearly identical to those previously observed in Er-doped As/sub 12/Ge/sub 33/Se/sub 55/ and As/sub 2/S/sub 3/ glass. This indicates that such broad, below gap PLE bands are not unique to Er-doped systems, but are more general features of rare earth-doped chalcogenide glass. The novel, broad PLE bands are attributed to absorption by below-gap defect and impurity-induced localized states in the host glass that are able to transfer their energy efficiently to the rare earth dopants. A phenomological explanation of the energy transfer process is presented.