Laser Host Materials Research Articles

Growth, rietveld refinement, Raman spectrum and dislocation of Ca2+/Mg2+/Zr4+-substituted GGG: a potential substrate and laser host material

Growth, rietveld refinement, Raman spectrum and dislocation of Ca2+/Mg2+/Zr4+-substituted GGG: a potential substrate and laser host material

Quantitative analysis of element substitution in mixed-vanadate LuxGd1-xVO4 single crystals at the atomic scale

In mixed crystals, two or more elements exhibit comparable properties and can be substituted freely. As a special type of “substitutional doping,” the properties of materials can be adjusted by altering the doping ratio of elements. Mixed-vanadate crystal LuxGd1-xVO4 is a promising laser host material with excellent chemical stability, mechanical property and thermal conductivity. The substitutional doping ratio of the two rare-earth elements determines the value of x. The thermal, optical, and laser properties of the material vary with x. However, the two types of atoms showing little difference in the same location in mixed crystals form substitutional solid solutions with alike atomic radii as well as electronic structures. Therefore, distinguishing comparable elements in mixed crystals at the atomic scale and quantitatively analyzing the doping ratio in mixed crystals are challenging. In this study, combining high-angle annular dark field (HAADF) and electron energy-loss spectroscopy (EELS), we accurately characterize the atomic structure of mixed-vanadate single crystal LuxGd1-xVO4 along the [111] orientation as well as the distribution of two rare-earth elements at the atomic scale. The ratio of Lu and Gd and the doping rules in the crystals are quantitatively analyzed. In addition, combined with the energy dispersive X-ray spectroscopy (EDS) results of the [100] crystal orientation, a uniform random distribution of Lu and Gd in the LuxGd1-xVO4 crystal is confirmed. This study provides a new means of understanding mixed-crystal structures and solves the problem of quantitative analysis of elemental doping in materials at the atomic scale, thus laying the foundation for exploring the relationships among composition, structure, and function in materials.

Effect of high energy radiation on electrical properties of synthetic bone materials

AbstractHydroxyapatites have been investigated since past six decades as laser host materials. Because of their important roles in bone and teeth, these have been subjects of recent investigations. Gallium and titanium have great potential for decreasing the depletion of calcium and reducing osteoporosis. The electrical properties and polarity play important roles in regeneration of the bones. We observed growth of grains in selenium‐doped gallium and titanium containing silicate hydroxyapatites. Observed morphology showed non‐facetted microstructures and it helped in achieving larger grains. For the material processed for the period of longer than 70 h, we did not observe any difference in the dielectric constant and resistivity of the selenium‐doped materials. For irradiating the materials, a Cs‐137 γ‐radiation with 5 µm curie dose was used up to 100 h. We observed that the dielectric constant and resistivity at different frequencies ranging from 100 to 100 000 Hz were affected by the high energy radiation. However, bias voltage in the range of 50–1 000 mV did no alter the dielectric constant or resistivity. This indicated that the breakdown of the material did not occur for this bias range.

High‐temperature phase transformation and thermodynamic properties of Ca3(VO4)2

AbstractCa3(VO4)2 is a promising candidate for applications in ferroelectric, laser host, and optical materials owing to its unique whitlockite structure and excellent physicochemical properties. In this study, the Ca3(VO4)2 powder was fabricated via a conventional solid‐phase route in air, using V2O5 and CaO as precursors. The trigonal Ca3(VO4)2 belongs to the space group R3c, having unit cell parameters of a = 10.8074 Å, b = 10.8074 Å, and c = 37.98871 Å, respectively. Ca3(VO4)2 melts congruently at 1680 K, as determined from differential scanning calorimetry measurements of the thermal profile of the second heating test. Enthalpy changes in Ca3(VO4)2 were experimentally determined for the first time across temperatures between 573 and 1623 K by drop calorimetry. The temperature‐dependent molar heat capacity of Ca3(VO4)2 was calculated from the enthalpy changes at elevated temperatures. Thermodynamic properties (entropy, enthalpy, and Gibbs free energy changes) were also calculated. The thermodynamic properties measured in this study were further applied to evaluate the appropriate precursors for fabricating Ca3(VO4)2 via solid‐state calcination. The results strongly recommend the use of V2O5 and Ca(OH)2 precursors for preparing the Ca3(VO4)2 samples because of their thermodynamic advantages.

Two-Photon Absorption in Ca3(VO4)2 and Ca2.7Sr0.3(VO4)2 Crystals

Two-photon absorption has been systematically studied in Ca3(VO4)2 and Ca2.7Sr0.3(VO4)2 crystals, both of which are prospective nonlinear optical and laser host materials. A strong dependence of the two-photon absorption coefficients on the orientation of the laser beam polarization with respect to the optical c-axis of the crystals is revealed. The measured coefficients for perpendicular and parallel orientations were 50 ± 10 cm/TW and 19 ± 4 cm/TW in Ca3(VO4)2, and 18 ± 3 cm/TW and 10 ± 2 cm/TW in Ca2.7Sr0.3(VO4)2, respectively. Thus, to minimize optical losses caused by two-photon absorption, an orientation of Ca2.7Sr0.3(VO4)2 crystals with the laser beam polarization parallel to the crystal optical c-axis is preferred.

Review of Green Synthesis and Anticorrosion Applications for Yttrium Oxide Nanoparticles

Corrosion processes cause considerable losses in industry and the economy. Corrosion inhibitors have been used in both inorganic and organic forms for a long time. Nanomaterials are more effective at preventing corrosion than traditional materials because they have a higher surface-to-volume ratio. Metal oxide nanoparticles (NP) are also novel in a variety of technological applications due to their distinct physical and chemical properties. Due to their higher dielectric constant and thermal stability, yttrium oxide (Y2O3) nanoparticles (NPs) are well known for technical applications. It is frequently utilized in electrochemical applications, photodynamic treatment, and other sectors as a host material for a range of rare-earth alloying elements. As a polarizer, phosphor, biosensor, laser host material, and for bioimaging, Y2O3 NPs has also been employed. Anti-corrosion characteristics of yttrium oxide nanoparticles are appealing regarding the formation of a smooth adsorbed layer on metal surfaces or alloys. This review focuses on Y2O3 NPs promising usage and developments in corrosion-inhibiting applications. The processes of green, chemical, hydrothermal and sol-gel nanoparticle synthesis are discussed.

3.1 μm mid-infrared luminescence in Er3+ doped ZnF2 modified aluminum fluoride glass

Herein, melt-quenching and Er3+ doping were used to synthesize fluoride glass specimens with low phonon energies (582 cm−1). These glass specimens exhibit intense 3.1 μm mid-infrared band emission when they are excited by a 980 nm laser diode, achieving a full width at half maximum (FWHM) of about 166 nm. This 3.1 μm emission intensity is enhanced by the introduction of ZnF2 to the AlF3-based fluoride glass. Up-conversion emission, strong near-infrared emission, and fluorescence lifetime are enhanced to different degrees by increasing the ZnF2 content. Moreover, the spectroscopic characteristics of the glass specimens and the highly efficient Er3+: 4S3/2 → 4F9/2 transition's energy transfer mechanism were investigated. The absorption spectra and emission spectra of these aluminum fluoride glass specimens were used to calculate their gain coefficients and maximum cross sections at 1.5 and 3.1 μm. Overall, the spectral properties of these prepared aluminum fluoride glass specimens demonstrate their high potential for use as infrared laser host materials.

Nd3+ doped [formula omitted] glass systems: Structural and optical properties

The structural and optical characteristic features of B2O3 + Li2O + CaO + CaF2 (BLCofNd) glasses incorporated with Nd3+ as a dopant of different concentrations (mol%) are reported. The X-ray diffraction technique was used to study structural characteristics such as the amorphous nature of BLCOFNd glass samples, Infrared spectroscopy was used to investigate the presence of functional groups and their impact on optical characteristics (FTIR), It reveals the creation of a network by borate and other components with the characteristics of glasses demonstrating different stretching and oscillating behavior of borate functional groups. The recorded UV Vis-NIR spectra of BLCofNd glasses reveal the prepared glasses have strong absorption at 584 nm in the visible region and 805 nm in the NIR region for the transitions 4I9/2→4G5/2 and 4I9/2→4F5/2, these transitions are due to the excitation of electrons by induced absorption. The density (gm/cc) measurements seem to be a rise in the values with a proportionality increase in CaO concentration (mol%), which directly relates to the decrease in the interionic distance (ri) making the glasses optically dense. Judd–Ofelt intensity parameters (Ω2, Ω4 and Ω6) highlights a covalency symmetry with a higher degree and surrounding lattice distribution of Nd3+ ions with other glass elements present in the network. The radiative properties of BLCOFNd glass samples mainly relate to parameters of radiative transition probability (AR), and corresponding branching ratios (βcal and βrad), which are derived from oscillator strength (fexp) measurements, FWHM or peak bandwidth (Δλp), stimulated emission cross-section and gain bandwidth (σse. Δλp) foresees that BLCofNd glasses are best candidates for laser host materials. The neodymium-doped borate glass exhibits a high peak power due to its emission at 1.049 μm wavelength and has its applications as lasing material and is prominently used as a source to produce the secondary waves in the measurement of pollutants in the atmosphere, optical amplifiers, and in the industry for their high intensity in emitted radiation.

Influence of impurity configuration on electronic and optical properties of Ce-doped YVO4: Semi-local & hybrid functionals

We investigate the impact of impurity configuration on electronic and optical properties of YVO4 through application of plane-wave DFT. Since this crystal is a common host material for optical devices and it has been widely used as a phosphor and a laser host material, it is important to identify a correlation between impurity location and the intrinsic properties of the material. To further improve the accuracy of the results several semi-local and a hybrid functional are tested. To find the most stable structure among possible configurations of doping, the electronic structures and formation energies of the available configurations are calculated and compared. We report that while the valence is formed by O-2p orbitals and conduction is made of V-3d orbitals in all configurations, the band width varies with the impurity configuration. Additionally, the formation energy is changing depending on where the dopant is located. Then the absorption coefficient and the refractive index are obtained using a modified HSE functional.

Studying the Nonlinear Optical Properties of Fluoride Laser Host Materials in the Ultraviolet Wavelength Region

Fluoride host materials doped with trivalent cerium ions have previously been demonstrated as successful laser materials in the ultraviolet wavelength region. However, the nonlinear optical properties of the fluoride hosts in this wavelength region have not been investigated yet, although nonlinearity could result in undesirable effects such as self-focusing and pulse distortion when these fluoride materials are used as gain media in high-power, ultrashort pulse laser oscillator and amplifier systems. In this work, the nonlinear refractive index of lithium calcium aluminum fluoride (LiCaAlF6), lithium strontium aluminum fluoride (LiSrAlF6), lanthanum fluoride (LaF3), and yttrium lithium fluoride (YLiF4) fluoride host materials are determined using the Kramers–Krönig relation model in the ultraviolet wavelength region. Self-focusing conditions, particularly at the peak laser emission wavelength of these materials, are further analyzed. Results show that LiCaAlF6 has the smallest nonlinear refractive index and self-focusing, making it an ideal host material under the conditions of ultrashort pulse and ultrahigh-power laser generation.

Surface and Subsurface Quality Assessment of Polished Lu2O3 Single Crystal Using Quasi-Brewster Angle Technique

The sesquioxide Lu2O3 single crystal has attracted tremendous attention as potential host material for high-power solid-state lasers. As polishing is the terminal process of conventional ultra-precision machining, the quality of polished crystal directly impacts the crucial performance indicators of optics. The high melting point of Lu2O3 single crystal makes crystal preparation difficult. Therefore, investigations on the surface/subsurface quality inspection of polished Lu2O3 single crystal are scarce. In this paper, we utilize the quasi-Brewster angle technique (qBAT) based on ellipsometry to inspect the quality of polished Lu2O3 single crystal, achieving fast, non-destructive, and high-sensitive surface/subsurface damage assessment. A systematic crystal processing scheme is designed and polished Lu2O3 crystal samples are obtained. To verify the results of qBAT, the surface and subsurface quality are tested using optical profilometer and transmission electron microscope, respectively. The consistency of the test results demonstrates the feasibility, high sensitivity, and accuracy of the qBAT. To our knowledge, this is the first time that the qBAT is applied to investigate the polished surface/subsurface quality of Lu2O3 single crystal. In conclusion, this method provides a powerful approach to the high-precision characterization of the surface/subsurface quality of Lu2O3 single crystal, and has significant potential for material property study and process optimization during ultra-precision machining.

Spectroscopic and luminescent properties of Nd3+-Al3+ co-doped silica glass prepared by spark plasma sintering

The Nd3+-Al3+ co-doped silica glass has drawn much attention due to the stability and efficient lasing emissions, while the high preparation temperature and residual hydroxyl groups restrict the further improvement of optical performance. In this work, transparent Nd3+-Al3+ co-doped glasses have been synthesized by spark plasma sintering at 980°C within 10 mins. Besides, adopting mesoporous powders as raw materials is beneficial to the homogeneous dispersion of ions in the glass. The transmittance, structure and luminescent properties were systematically investigated. The Judd-Ofelt intensity parameters were obtained to analyze the Al3+ co-doping effects. The PL intensity strongly depends on the ions concentration and the best value is obtained when the Nd3+ concentration is 1.0 mol% and ratio of Nd:Al is 1:7. In addition, the calculated emission cross section is 2.12, which is larger than the majority of previously reported values, suggesting that as-prepared silica glasses are candidates for laser host materials.

Supercontinuum generation in single-crystal YAG fibers pumped around the zero-dispersion wavelength.

Yttrium aluminum garnet (YAG) is a common host material for both bulk and single-crystal fiber lasers. With increasing interest in developing optical technologies in the short-wave infrared and mid-infrared wavelength range, YAG may be a potential supercontinuum medium for these applications. Here, we characterize femtosecond laser pumped supercontinuum generation with 1200-2000 nm pump wavelengths (λp) for undoped, single-crystal YAG fibers, which are representative of the normal, zero, and anomalous-dispersion regimes. Supercontinuum was observed over the spectral region of about 0.2 to 1.6λp. Z-scan measurements were also performed of bulk YAG, which revealed little dispersion of the nonlinear index of refraction (n2) in the region of interest. The measured values of n2 (∼1×10-6cm2/GW) indicate a regime in which the nonlinear length, LNL, is less than the dispersion length, LD, (LNL≪LD). We report intensity clamping of the generated filament in the normal group velocity dispersion (GVD) regime and an isolated anti-Stokes peak in the anomalous GVD regime, suggesting further consideration is needed to optimize supercontinuum generation in this fiber medium.

Czochralski growth of mixed cubic sesquioxide crystals in the ternary system Lu2O3–Sc2O3–Y2O3

Cubic rare-earth sesquioxide crystals are strongly demanded host materials for high power lasers, but due to their high melting points investigations on their thermodynamics and the growth of large-size crystals of high optical quality remain a challenge. Detailed thermal investigations of the ternary system Lu2O3–Sc2O3–Y2O3 revealing a large range of compositions with melting temperatures below 2200°C and a minimum of 2053°C for the composition (Sc0.45Y0.55)2O3 are presented. These reduced temperatures enable for the first time the growth of high optical quality mixed sesquioxide crystals with disordered structure by the conventional Czochralski method from iridium crucibles. An (Er0.07Sc0.50Y0.43)2O3 crystal is successfully grown and characterized with respect to its crystallographic properties as well as its composition, thermal conductivity and optical absorption in the 1 µm range.

Excellent performance of a cryogenic Nd:YAlO3 laser with low wavefront distortion based on zero thermal expansion.

High-power solid-state lasers with good beam quality are attracting great attention on account of their important applications in industry and military. However, the thermal effects generated in the laser host materials seriously limit power scaling and degrade the beam quality. Thermal lensing and thermally induced wavefront deformation are the main causes of the beam quality deterioration. Here we investigate the performance of a zero thermal expansion (ZTE) solid-state laser gain material. In a proof-of-principle experiment, an ${a}$-cut rod ${\rm Nd}\!:\!{{\rm YAlO}_3}$ (Nd:YAP) perovskite crystal is chosen to be the gain medium for ZTE around 180 K. The laser performance spanning the temperature range from 80 to 290 K is studied. The maximum output power and minimum threshold pump power were obtained at a temperature of 180 K. Moreover, the measured thermal focal power and peak-to-valley value of the wavefront distortion also reach a minimum at this temperature, an additional benefit from the crystal's ZTE coefficient. We envisage that these results will open a new route towards the development of high-power and high-beam-quality lasers through the use of ZTE gain materials.

Yttrium Oxide Nanoparticle Synthesis: An Overview of Methods of Preparation and Biomedical Applications

Metal oxide nanoparticles demonstrate uniqueness in various technical applications due to their suitable physiochemical properties. In particular, yttrium oxide (Y2O3) nanoparticle is familiar for technical applications because of its higher dielectric constant and thermal stability. It is widely used as a host material for a variety of rare-earth dopants, biological imaging, and photodynamic therapies. Y2O3 has also been used as a polarizer, phosphor, laser host material, and in the optoelectronic fields for cancer therapy, biosensor, and bioimaging. Yttrium oxide nanoparticles have attractive antibacterial and antioxidant properties. This review focuses on the promising applications of Y2O3, its drawbacks, and its modifications. The synthetic methods of nanoparticles, such as sol-gel, emulsion, chemical methods, solid-state reactions, combustion, colloid reaction techniques, and hydrothermal processing, are recapitulated. Herein, we also discuss the advantages and disadvantages of Y2O3 NPs based biosensors that function through various detection modes including colorimetric, electrochemistry, and chemo luminescent regarding the detection of small organic chemicals, metal ions, and biomarkers.

High content Er3+ doped ZBLAN glass: The spectral characteristics and high slope efficiency MIR laser investigation

The ZBLAN glass with high content of Er3+ was prepared and studied. The glass has a wide infrared transmittance range of 2.5–8.0 µm, which means a lower maximum phonon energy. By testing and analyzing the fluorescence spectrum and lifetime curves under different penetration depths, the intrinsic emission spectrum and lifetime of the sample are obtained without the influence of sub-absorption. Under 980 nm excitation, the maximum emission cross section and the lifetime of 2.7 µm are 6.10 × 10−21 cm2 and 6.49 ms, indicating that high-concentration doping has a larger laser quality factor. According to the rate equation and transmission equation, cascaded and non-cascaded fiber laser models are established to conduct research on 2.7 µm fiber lasers. The slope efficiency can reach 40.38% at a pump wavelength of 980 nm and a fiber background loss of 0.1 dB/m. The high emission cross section, long fluorescence lifetime and high slope efficiency output make ZBLAN glass heavily doped with Er3+ an ideal host material for mid-infrared lasers.

Dy3+ doped B2O3 – Li2O – CaO – CaF2 glass for efficient white light emitting sources

In this present work, Dy3+ doped B2O3 – Li2O – CaO – CaF2 (BLCFDy) glasses with variable concentrations of alkaline and alkaline earth oxide elements are prepared. The X – Ray diffraction technique has been carried out to verify the non crystallinity of BLCFDy glasses. The Fourier Transform Infrared (FT-IR) study reveals that, the structural properties of glasses exhibiting stretching and vibrational groups of various borate groups. The Optical absorption spectroscopy in Ultraviolet – Visible and Near Infrared regions provides glasses have strong absorption in NIR region for excitations 6H15/2 → 6F7/2 (895nm), 6F9/2 (1084nm), 6H9/2 (1267nm) and 6H11/2 (1686nm) states. The Optical band gap measurements prove existence of non-bridging oxygens (NBOs), localization of charges and donor centres in prepared glass samples. Judd–Ofelt hypothesis and intensity parameters (Ω2,Ω4 andΩ6) predicts higher degree of symmetry in covalency and encompassing environment of Dy3+ ions with constituent ligand elements. The radiative properties of glass samples like radiative transition probability (AR), branching ratios both calculated and experimental (βcal & βrad), peak band width (∆λp), stimulated emission cross – section and gain band width (σse x ∆λp) predicts that prepared glasses are good host of lasing materials and optical gain medium. The Photoluminescence emission spectra exhibits two principle strong emissions at 484nm (Blue), 575nm (Yellow) and observable emission at 664nm (Red) owing to de-excitation from 4F9/2 to respective 6H15/2, 6H13/2 and 6H11/2 states. CIE - 1931 chromaticity coordinates (x, y) and CCT values are calculated from photoluminescence emission spectra were found to be within the white light region of the CIE. For the glasses BLCFDy2 and BLCFDy3 colour coordinates (x, y) are (0.34, 0.37), (0.34, 0.38) respectively. The corresponding CCT values are 5223K and 5237K. Thus, BLCFDy2 and BLCFDy3 are the potential candidates for fabrication of white light emitting diodes (W – LEDs) also as laser host materials.

The growth of a large GdPO4 crystal guided by theoretical simulation and the study of its phonon properties.

It has remained a big challenge to grow large crystals of compounds at very anisotropic crystal growth rates. GdPO4 is such an example, which usually grows into a needle-like shape. This work solved this problem by using Li+ ions, predicted by first-principles calculations, to adjust the crystal morphology of GdPO4. Based on the calculated surface energies and the polar properties of the surfaces, we identified two crystal planes, i.e. (-102) and (-111), which can be used to adjust the morphology of the GdPO4 crystal by using extrinsic cations in the flux system. With a predicted Li containing flux system, Li2O-MoO3-B2O3, a large crystal with a record size, 10.0 × 9.0 × 18.2 mm3, was grown by using the top-seeded solution growth (TSSG) method. Based on the grown large crystal and the polarized Raman measurements, four new Raman bands missing in early studies and other bands were unambiguously assigned. By introducing a new formula, the phonon-phonon interactions were shown to be weak in the temperature range from 83 to 803 K. Our study indicates that the crystal of GdPO4 can be used as a promising laser host material working under relatively high temperature conditions.

Determination of single crystal elastic moduli of KTb3F10 by resonant ultrasound spectroscopy

KTb3F10 (KTF) has been developed in recent years as a candidate Faraday rotator material because of its cubic symmetry, high figures of merit, and low absorption coefficient. While considerable efforts have focused on crystal growth and optical properties, investigations of fundamental thermodynamic behavior of KTF have been limited. Here, we report elastic moduli C11, C12, and C44 of single crystalline KTF measured by resonant ultrasound spectroscopy from 280 K up to 300 K and the obtained temperature derivatives of each modulus. We additionally report the single crystal elastic moduli of the rare-earth garnet Y3Al5O12 (YAG), yielding results that agree well with the prior literature. We found C11=135.62 GPa, C12=58.11 GPa, and C44=44.81 GPa for KTF and C11=332.43 GPa, C12=109.58 GPa, and C44=114.81 GPa for YAG at room temperature. The present results have been compared with previous experimental and theoretical results and with common oxide and fluoride optical materials, revealing the relative softness of KTF. The low elastic moduli of KTF are, in turn, responsible for its low thermal conductivity and low Debye frequency compared to other laser host materials.