Studies on boro cadmium tellurite glasses

To investigate the modification effect of the modifier CdO on boro tellurite glass, a series of glasses with compositions (50 − x) CdO-xTeO₂-50B₂O₃ have been prepared by conventional melt quenching technique. Optical absorption, IR and Raman structural studies are carried out on the glass system. The optical absorption studies revealed that the cutoff wave length and refractive index increase while optical band gap (E_opt) and Urbach energy decreases with increase of CdO content. The IR and Raman studies revealed that structure of glass network consists of [TeO_3]/[TeO₃₊₁], [TeO₄], [BO₃], [BO₄] and [Cd-Te] linkages .The compositional dependence of different physical parameters such as density, molar volume, oxygen packing density, optical basicity, have been analyzed and discussed.     

FTIR spectroscopic study of some bismuth germanate glasses containing gadolinium ions

Since infrared spectroscopy and density are advantageous tools for the investigations of glasses, we have used them to obtain information concerning the local structure of xGd₂O₃·(100 − x)[4Bi₂O₃·GeO₂] glass system, with 0 ≤ x ≤ 30 mol%. Gd₂O₃ play the network modifier role in the studied glasses and determines, by progressive addition, the increase of structural volume difference between the hypothetical crystalline compounds and the quenched samples. FTIR spectroscopy data show that the glass structure consists on the BiO₆, GeO₄ and GeO₆ structural units, and the conversion among these units mainly depends on the Gd₂O₃ content.     

Oxyfluorotellurite glasses doped by dysprosium ions. Thermal and optical properties

The paper shows results of investigation of thermal and optical properties of oxyfluorotellurite (65 − x)TeO₂–20ZnF₂–12Pb₂O₅–3Nb₂O₅–xDy₂O₃ (x = 0.5, 2 and 5) glass systems. Thermal stability and the onset of crystallization of the materials were monitored by differential thermal analysis (DTA). It was found that characteristic parameters, namely glass transition temperatures (T_g), onset of crystallization temperatures (T_c) and thermal stability criteria ΔT and H’ increased with increasing Dy₂O₃ content indicating that the incorporation of dysprosium ions improves substantially thermal stability of glass system under study.Optical absorption and emission spectra of Dy³⁺ ions in oxyfluorotellurite glass were investigated at room temperature in the visible (VIS) and near-infrared (NIR) region. Oscillator strengths, phenomenological Judd–Ofelt (JO) intensity parameters Ω_2,4,6, radiative transition probabilities, branching ratios and radiative lifetimes of luminescent levels were determined. Decay curves of the ⁴F_9/2 luminescence of incorporated Dy³⁺ ions were recorded and analysed. Lifetimes and the luminescence dynamics were studied as a function of the Dy₂O₃ concentration. It was concluded that good thermal stability combined with desirable spectroscopic parameters of investigated dysprosium-doped oxyfluorotellurite glass point at the suitability of this material for the design of UV-excited visible phosphors.     

Effect of substrate temperature on the optical parameters of thermally evaporated Ge-Se-Te thin films

Thin films of Ge₁₀Se_90 − xTe_x (x = 0, 10, 20, 30, 40, 50) glassy alloys were deposited at three substrate temperatures (303 K, 363 K and 423 K) using conventional thermal evaporation technique at base pressure of ~ 10^− 4 Pa. X-ray diffraction results show that films deposited at 303 K are of amorphous nature while films deposited at 363 K and 423 K are of polycrystalline nature. The optical parameters, refractive index and optical gap have been derived from the transmission spectra (using UV-Vis-NIR spectrophotometer) of the thin films in the spectral region 400-1500 nm. This has been observed that refractive index values remain almost constant while the optical gap is found to decrease considerably with the increase of substrate temperature. The decrease in optical gap is explained on the basis of change in nature of films, from amorphous to polycrystalline state, with the increase of substrate temperature. The optical gap has also been observed to decrease with the increase of Te content.     

Spectroscopy and frequency upconversion of Er ions in fluorotellurite glasses

In this work we report the optical properties and upconversion luminescence of Er³⁺ ions in TeO₂–WO₃–PbO–BaF₂ and TeO₂–TiO₂–Nb₂O₅–BaF₂ fluorotellurite glasses and their comparison with those of TeO₂–TiO₂–Nb₂O₅ glass. The optical properties of Er³⁺ ions have been established in terms of absorption and emission spectra and lifetime measurements. The 1.5 μm emission cross-section has been determined from the line shape of the emission spectrum and the calculated emission probability for the ⁴I_13/2 level. The highest emission cross section (6.9 × 10⁻²¹ cm²) corresponds to the TeO₂–TiO₂–Nb₂O₅–BaF₂ glass with a figure of merit for the bandwidth of 524.4 cm² nm. Upconversion emissions at 530, 548 nm, and 660 nm have been obtained under infrared excitation at 800 nm in the ⁴I_9/2 level and compared with those obtained under one photon excitation. The green emission corresponding to the ⁴S_3/2 → ⁴I_15/2 transition is dominant in all glasses. The excitation wavelength dependence of the upconverted luminescence together with its time evolution after infrared pulsed excitation suggest that energy transfer upconversion processes are responsible for the green upconversion luminescence.     

Excited state characteristics of the Li2B4O7 and KLiB4O7 glasses activated by Cr3+ ions

The excited state characteristics by means of the excited state absorption (ESA), optical gain and bleaching spectra have been measured for prototype glasses with Li₂B₄O₇ (LBO) and KLiB₄O₇ (KLBO) compositions activated by Cr³⁺ ions. The work addressed to search for novel attractive media for broadband lasers and amplifiers, is a completion of detailed spectroscopic evaluation described in earlier papers. One of the examined materials (KLBO), in accordance with optimistic comments given in previous work, reveals a very broad gain spectrum in the near IR, which itself is interesting in view of very few reports on glasses showing optical gain for Cr³⁺ ions in the low-field local environment. The ESA/gain/bleaching spectra, registered with equipment of improved sensitivity, have been reproduced by calculations, and detailed single configuration coordinate diagram, based on experimental data, has been created for interpretation.     

Measurement of the refractive index and thickness of a transparent film from the shift of the interference pattern due to the sample rotation

A method is described for the simultaneous measurement of the refractive index and thickness of a transparent film. The method is based on the rotational shift of the interference pattern caused by the change of the light incidence angle. The refractive index is evaluated without any prior information about film thickness or about the substrate and its refractive index. In addition, the roughness of the interfaces and/or the presence of an unidentified thin layer are not important. In two experimental examples, the refractive index and thickness are measured for a GaN thin film and a cling-film.     

Optical absorption and fluorescent behaviour of titanium ions in silicate glasses

Titanium in normal melting conditions in air atmosphere present as Ti⁴⁺ ion in basic silicate glasses exhibited an ultra-violet cut-off in silicate glasses, viz. soda-magnesia-silica, soda-magnesia-lime-silica and soda-lime-silica glasses. This indicates that Ti⁴⁺ ion can be a good replacement for Ce⁴⁺ ion in producing UV-absorbing silicate glasses for commercial applications. The wavelength maxima at which the infinite absorption takes place in glasses was found to be around 310 nm against Ti-free blank glass in UV-region. The mechanism of electronic transition from O^2- ligands to Ti⁴⁺ ion was suggested as L→ M charge transfer. The low energy tails of the ultra-violet cut-off were found to obey Urbach’s rule in the optical range 360–500 nm. The fluorescence spectra of these glasses were also studied and based on the radiative fluorescent properties it was suggested that the soda-lime-silica glass containing Ti⁴⁺ ion with greater emission cross-section would emit a better fluorescence than the corresponding soda-magnesia-lime-silica and sodamagnesia-silica glasses. The shift of emission wavelengths maxima towards longer wavelength in titania introduced silicate glasses was observed on replacement of MgO by CaO which may be attributed due to an increase in basicity of the glass system.     

A study of neutron and gamma radiation effects on transmission of various types of glasses, optical coatings, cemented optics and fiber

A study of radiation effects on various types of glasses, dielectric optical coatings, cemented optics and fiber was undertaken with a view to select them for extreme radiation environments. Samples were exposed to different radiation doses in the Pakistan Research Reactor-I (PARR-I) for neutron and Cobalt 60 source for gamma irradiation. Transmissions were measured before and after irradiation. The dielectric coatings were subjected to additional tests (adhesion, abrasion and humidity, etc.) as per MIL-M-13508C and MIL-C-675C. All 15 glasses studied showed varying amounts of transmission loss as expected, with negligible degradation for three types. Recovery of transmissions with time/ageing was also studied, with more or less complete recovery with temperature annealing. A faster bleaching of darkened/brown glasses was achieved by using UV lamps or UV laser. The dielectric coatings (HR, AR) and one of the two commercial optical cements showed excellent resistance to neutrons and gamma radiations, and could be good candidates for the fabrication and utilization of optical components in extreme radiation environments. The data allowed several Chinese glasses to be studied for the first time.     

Influence of substrate absorption on accuracy of determination of refractive index and thickness of uniform thin chalcogenide Cu1[As2(S0.5Se0.5)3]99 film

The envelope method is a commonly used method for determination of some important optical constants, by using the envelopes of the transmittance T(λ) and/or reflectance R(λ) spectrum of the thin film deposited on transparent substrate. Two envelope methods were carried out in this paper: standard—method which assumes that substrate is absolutely transparent and modified—method which takes substrate absorption into account.The investigated sample is a uniform thin chalcogenide Cu₁[As₂(S_0.5Se_0.5)₃]₉₉ film, deposited onto two kinds of a weakly absorbing substrates that differ in thickness.It was shown that the degree of accuracy in determination of chosen optical parameters for both investigated samples is notably improved when the absorbance of the bare substrates is considered in the expressions for the envelopes.     

Erbium doped tellurite glasses with improved thermal properties as promising candidates for laser action and amplification

The influence of composition on the thermal stability of tellurite glasses was investigated by using differential scanning calorimetry (DSC). The studied glasses were synthesized by conventional melting quenching method. The best thermal stability and poor crystallization tendency were obtained for the glass composed of 65TeO₂–15ZnO–10Na₂O–5BaO–3La₂O₃ doped with Er₂O₃ (2 mol %). This glass will be referred, in this article, as TZNBL: Er³⁺ glass.The spectroscopic properties of the above glass are investigated based on the Judd–Ofelt and McCumber theories.The calculated intensity parameters (Ω_2,4,6) are compared to those obtained for Er³⁺ in other glasses. The radiative emission rate has been calculated for the different Er³⁺emitting levels. The high values of Ω₄ and Ω₆ confirm the results of the DSC experiment concerning the rigidity of the studied glass.Absorption, emission and gain cross section of the ⁴I_13/2 ↔ ⁴I_15/2 (Er³⁺) transition in the studied glass are reported and the results are compared to those of other glasses.The ⁴I_13/2 ↔ ⁴I_15/2 (Er³⁺) absorption and emission cross sections derived by the application of the Mc Cumber’s theory corroborate the Judd–Ofelt results.The whole of results demonstrate that the new composition leads to good thermal and mechanical properties as well efficient Er³⁺ absorption, emission cross sections, which make this glass as a promising candidate for laser action and amplification.     

Dielectric properties of NaF-B2O3 glasses doped with certain transition metal ions

Dielectric constant ε, loss tan δ, a.c. conductivity Σ and dielectric breakdown strength of NaF-B₂O₃ glasses doped with certain transition metal ions (viz. Cu²⁺, VO²⁺, Ti⁴⁺ and Mn⁴⁺) are studied in the frequency range 10²-10⁷ Hz and in the temperature range 30–250°C. The values of ε, tan δ, Σ_a.c. are found to be the highest for Cu²⁺ doped glasses and the lowest for Mn⁴⁺ doped glasses. Activation energy for a.c. conduction and the value of dielectric breakdown strength are found to be the lowest for Cu²⁺ doped glasses and the highest for Mn⁴⁺ doped glasses. With the help of infrared spectra, increase in the values of ε and tan δ of these glasses with frequency and temperature are identified with space charge polarization. An attempt has been made to explain a.c. conduction phenomenon on the basis of quantum mechanical tunneling model (QMT)/carrier barrier hopping model.     

Dielectric properties of LiF-B2O3 glasses doped with certain rare earth ions

Dielectric constantɛ, loss tanδ and a.c. conductivityσ of LiF-B₂O₃: Ln³⁺ (where Ln=Ce, Pr, Nd and Tb) glasses are studied as functions of frequency (in the range 10²–10⁶ Hz) and temperature (range 30–200°C). The dielectric breakdown strength of these glasses was also determined at room temperature in an air medium. The rate of increase ofɛ and tanδ with temperature decreases with decrease in the ionic radius of RE³⁺ ion whereas the dielectric breakdown strength, the activation energy for a.c. conduction in the high temperature region decreases with increase in the ionic radius of RE³⁺ ion. An attempt has been made to explain the a.c. conduction in these glasses on the basis of quantum mechanical tunnelling (QMT) model.     

Temperature dependence of the band gap, refractive index and single-oscillator parameters of amorphous indium selenide thin films

InSe thin films are obtained by evaporating InSe crystal onto ultrasonically cleaned glass substrates under pressure of 10⁻⁵ Torr. The structural and compositional analysis revealed that these films are of amorphous nature and are atomically composed of 51% In and 49% Se. The reflectance and transmittance of the films are measured at various temperatures (300–450 K) in the incident photon energy range of 1.1–2.1 eV. The direct allowed transitions band gap – calculated at various temperatures – show a linear dependence on temperature. The absolute zero value band gap and the rate of change of the band gap with temperature are found to be (1.62 ± 0.01) eV and −(4.27 ± 0.02) × 10⁻⁴ eV/K, respectively. The room temperature refractive index is estimated from the transmittance spectrum. The later analysis allowed the identification of the static refractive index, static dielectric constant, oscillator strength and oscillator energy.     

Optical and electronic properties of some semiconductors from energy gaps

II-VI and III-V tetrahedral semiconductors have significant potential for novel optoelectronic applications. In the present work, some of the optical and electronic properties of these groups of semiconductors have been studied using a recently proposed empirical relationship for refractive index from energy gap. The calculated values of these properties are also compared with those calculated from some well known relationships. From an analysis of the calculated electronic polarisability of these tetrahedral binary semiconductors from different formulations, we have proposed an empirical relation for its calculation. The predicted values of electronic polarisability of these semiconductors agree fairly well with the known values over a wide range of energy gap. The proposed empirical relation has also been used to calculate the electronic polarisability of some ternary compounds.     

Structural and optical properties of phosphate-zinc-nickel oxide glasses for narrow band pass absorption filters

Novel two phosphate glass systems with compositions 50P₂O₅–30ZnO–20NiO and 50P₂O₅–30ZnO–20[NiCl_2–6H₂O] were prepared using a conventional melt-quench technique. The absorbance and transmittance were measured using a spectrophotometer in the spectral range between 190 and 1100 nm. The data demonstrates that the system acts as a narrow bandpass optical absorption filter, with a transmission band in the UV region of 311–376 nm, which is centred at 350 nm and has a full width half maximum (FWHM) of almost 34 nm, whereas, the red region is the UV region of 617–684 nm, and centred at 650 nm and has a full width half maximum (FWHM) of nearly 32 nm. However, the refractive index (n), optical band gap (E_opt), non-linear refractive index n₂, third order non-linear susceptibility χ⁽³⁾ and non-linear absorption coefficient β were also calculated. It was apparent that the non-linear refractive index, third order non-linear susceptibility and non-linear absorption coefficient increases by decreasing the optical energy gap. Finally, we investigated the structure of the prepared glasses by using Raman and FTIR spectra. We found that the local network structure based mainly on Q¹ and Q² tetrahedron units connected by P–O–P linkages.     

Influence of Ga3+ ions on spectroscopic and dielectric features of multi component lithium lead boro bismuth silicate glasses doped with manganese ions

Multi-component glasses of the chemical composition 19.5Li₂O–20PbO–20B₂O₃–30SiO–(10 − x)Bi₂O₃–0.5MnO:xGa₂O₃ with 0 ≤ x ≤ 5.0 have been synthesized. Spectroscopic (optical absorption, IR, Raman and ESR) and dielectric properties were investigated. Optical absorption and ESR spectral studies have indicated that managanese ions do exist in Mn³⁺ state in addition to Mn²⁺ state in the samples containing low concentration of Ga₂O₃. The IR and Raman studies indicated increasing degree of disorder in the glass network with the concentration of Ga₂O₃ up to 3.0 mol%. The dielectric constant, loss and ac conductivity are observed to increase with the concentration of Ga₂O₃ up to 3.0 mol%. The quantitative analysis of the results of dielectric properties has indicated an increase in the insulating strength of the glasses as the concentration of Ga₂O₃ is raised beyond 3.0 mol%. This has been attributed to adaption of gallium ions from octahedral to tetrahedral coordination.     

Low-Loss Optical Waveguides for the Near Ultra-Violet and Visible Spectral Regions with Al(2)O(3) Thin Films from Atomic Layer Deposition

In this work, we report low-loss single-mode integrated optical waveguides in the near ultra-violet and visible spectral regions with aluminum oxide (Al₂O₃) films using an atomic layer deposition (ALD) process. Alumina films were deposited on glass and fused silica substrates by the ALD process at substrate/chamber temperatures of 200 °C and 300 °C. Transmission spectra and waveguide measurements were performed in our alumina films with thicknesses in the range of 210-380 nm for the optical characterization. Those measurements allowed us to determine the optical constants (n_w and k_w), propagation loss, and thickness of the alumina films. The experimental results from the applied techniques show good agreement and demonstrate a low-loss optical waveguide. Our alumina thin-film waveguides are well transparent in the whole visible spectral region and also in an important region of the UV; the measured propagation loss is below 4 dB/cm down to a wavelength as short as 250 nm. The low propagation loss of these alumina guiding films, in particular in the near ultra-violet region which lacks materials with high optical performance, is extremely useful for several integrated optic applications.     

Effect of Ag nanoparticles on the radiative properties of tellurite glasses doped with Er3+, Yb3+ and Tm3+ ions

The present work is devoted to the characterization of the thermal and spectroscopic properties of tellurite glasses, codoped with Er³⁺, Yb³⁺ and Tm³⁺ rare-earth ions and silver nanoparticles (NPs). The techniques used for this investigation were UV–visible and infrared absorption, time-resolved luminescence and thermal lens. Time-resolved luminescence studies indicate efficient Yb³⁺ → Er³⁺ and Yb³⁺ → Tm³⁺ energy transfers and intense Er³⁺ and Tm³⁺ mid-infrared emissions around 1550 nm and 1860 nm, respectively. The presence NPs is found to increase the thermal diffusivity of the materials and to shorten the mid-infrared emission lifetime of both the Er³⁺ and Tm³⁺ ions.     

Spectroscopic studies of Nd-doped alkali fluoroborophosphate glasses

A new family of three optical glasses of the following chemical composition with 1 mol% of Nd³⁺ were prepared to examine the effects of alkali fluorides in unmixed form:

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, where RF=LiF, NaF and KF. On the basis of the measured values of densities and refractive indices, the dielectric constant, reflection losses, molar refraction, Nd³⁺ ion concentration in glasses and several other physical properties were determined. Absorption spectra of these glasses were recorded and Judd–Ofelt intensity parameters (Ω_λ) have been calculated. Radiative lifetimes (τ_R) and branching ratios (β_R) for the fluorescent levels have been determined. To understand the laser efficiency of these materials, the values of the spectroscopic quality factor (Ω₄/Ω₆) has been evaluated and it is found that glass C could be suggested as a suitable lasing material.