Tungsten Tellurite Glasses Research Articles

Intense Upconverted White Light Emission from Tm3+ - Er3+ - Yb3+ Doped Zinc Tungsten Tellurite Glasses

The different amount of rare earth ions doped zinc tungsten tellurite glasses with the compositions (70-x-y-z)TeO 2 – 20ZnO – 10WO 3 – xEr 2 O 3 – yTm 2 O 3 – zYb 2 O 3 (x = 0.3, 0.5; y = 0.3, 0.5; z = 3) have been synthesized using melt quenching technique. Blue, green, red and infrared luminescence via energy transfer and frequency upconversion mechanisms in Tm 3+ /Er 3+ /Yb 3+ triply-doped zinc tungsten tellurite glasses were investigated under single 975 nm diode laser excitation. Intense blue (Tm 3+ : 1 D 2 → 3 F 4 , 1 G 4 → 3 H 6 ; 477 nm), green ( 2 H 11/2 , 4 S 3/2 → 4 I 15/2 ; 525 nm and 549 nm), red (Er 3+ : 4 F 9/2 → 4 I 15/2 , Tm 3+ : 1 G 4 → 3 F 4 ; 659 nm) and infrared (Tm 3+ : 1 G 4 → 3 H 5 , 3 H 4 → 3 H 6 ; 807 nm) emissions were observed simultaneously at room temperature. Intense white light emission from all samples was observed with CCT values higher than 6500 K and CRI values lower than 80. The CIE coordinates of the emitted white light were found to shift to yellowish-greenish region with increasing pumping power. The possible energy transfer and upconversion mechanisms are discussed and plausible explanations are made.

Photon upconversion in Ho3+-Yb3+ embedded tungsten tellurite glass

This article reports on the frequency upconversion property of yellow light emitting Ho3+-Yb3+ embedded tungsten tellurite (TeO2-WO3) glass prepared by the famous melt-quench technique. Holmium activated TeO2-WO3 glass gives efficient visible and near-infrared upconversion luminescence upon 980nm excitation, which improved via the incorporation of Yb3+ ions. The upconversion process was examined by a pump power dependence study that revealed the involvement of a single photon for upconversion emission around 886nm whereas two pump photons needed for the other emissions. The observed single and/or two photon upconversion feature is discussed with the help of a luminescence decay study and energy level diagram of the embedded ions.

Compositional dependence of broadband near-infrared downconversion and upconversion of Yb3+-doped multi-component glasses

Yb3+ single-doped glasses show a strong excitation band in the 300–400 nm region, and efficiently emit photons with wavelengths of 920–1150 nm, and have potential applications in solar cells operating in an extraterrestrial situation. In this work, we systematically study the broadband near-infrared downconversion and upconversion of Yb3+-doped silicate, germanate, phosphate, tellurite and tungsten tellurite glasses. All samples show a broad excitation band in the 300–400 nm range, which is attributed to the charge transfer of the Yb3+–O2− couple. The position of the charge transfer band (CTB) shifts from 300 nm to longer wavelengths around 350 nm when the length of the R–O(Si, P, Ge, Te) increases. The longer R–O gives rise to a smaller central void for Yb3+, thus resulting in a small proportion of Yb3+ ions, thus leading to the blue-shift of the CTB. A smaller proportion of Yb3+ in silicate glasses causes in the strongest upconversion emission at 500 nm.

Dy3+ ions doped single and mixed alkali fluoro tungsten tellurite glasses for LASER and white LED applications

A new-fangled series of Dy3+ ions doped Single and Mixed Alkali Fluoro Tungsten Tellurite Glasses have been prepared by using melt quenching technique and their spectroscopic behaviour was investigated by using XRD, optical absorption, photoluminescence and lifetime measurements. The bonding parameter studies reveal the ionic nature of the DyO bond in the present glasses. From the absorption spectra, the Judd-Ofelt (J-O) intensity parameters have been determined and in turn used to determine various radiative properties for the different emission transitions from the 4F9/2 fluorescent level. The photoluminescence spectra of all the glasses exhibit two intensified peaks in blue and yellow regions corresponding to the transitions 4F9/2 → 6H15/2 (483 nm) and 4F9/2 → 6H13/2 (575 nm) respectively. From the photoluminescence spectra, it is observed that the luminescence intensity is maximum for Dy3+ ion doped potassium combination of tungsten tellurite glass (TeWK:1Dy). The highest emission cross-section and branching ratio values observed for the 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 transitions suggest the possible laser action in the visible region from these glasses. By correlating the experimental lifetimes (τexp) measured from the decay spectral features with radiative lifetimes (τR), the quantum efficiencies (η) for all the glasses have been evaluated and found to be maximum for potassium combination tungsten tellurite (TeWK:1Dy) glass. The CIE colour chromaticity coordinates (x, y), (u, v), colour correlated temperature (CCT) and Y/B ratio were also estimated from the photoluminescence spectra for different compositions of glasses. The chromaticity colour coordinates evaluated for all the glasses fall within the white light region and white light emission can be tuned by varying the composition of the glass. From all these studies, it was concluded that 1 mol% of Dy3+ ions doped TeWK glass is more suitable for lasing and white-LED applications.

20 μm Nd^3+/Ho^3+-doped tungsten tellurite fiber laser

Tellurite glass has emerged as a promising ~2.0 μm laser material owing to its excellent features of supporting efficient mid-infrared emission and easy fiber-pulling over the commonly investigated glasses. In this paper, we report an efficient ~2.0 μm laser output from a new-type of Nd3+/Ho3+ co-doped tungsten tellurite fiber laser by using an ultra-short length fiber of 5 cm upon a 795 nm laser diode. The tellurite fibers have been fabricated by a suction technique with the core and cladding diameters of 32 and 125 μm, respectively. The propagation loss of the fiber is measured to be 4.44 dB/m at 1310 nm by using the cutback method. The large energy transfer coefficient from Nd3+ to Ho3+ (3.8 × 10−40 cm6·s–1) and high gain coefficient of Ho3+: 5I7 → 5I8 transition (1.2 cm–1) have confirmed the success of using Nd3+ as sensitizer to realize the ~2.0 μm laser emission of Ho3+. The maximum output power of the laser is obtained to be 12 mW at a center wavelength of 2052 nm with a slope efficiency of 11.2%. The laser threshold is as low as 38 mW, which is around one order of magnitude lower than the previously reported Tm3+/Yb3+ doped tellurite fiber lasers with the similar pump scheme and fiber geometry. The results indicate that the Nd3+/Ho3+ co-doped tungsten tellurite glass fiber laser is a promising laser medium candidate for achieving the ultra-compact and efficient ~2.0 μm laser.

Toward a mid-infrared femtosecond laser system with suspended-core tungstate-tellurite glass fibers.

A simple design of a fiber laser system for generating high-quality pulses with a duration of order 100 fs with ultrabroad wavelength tunability in the 2-5 μm range is discussed. This design incorporates conventional fs near-IR lasers and specially developed tungstate-tellurite fibers with two zero-dispersion wavelengths (ZDW) and relies on nonlinear wavelength conversion via either soliton self-frequency shift (SSFS) or red-shifted dispersive wave (DW) generation. The fiber parameters needed for such optical conversion have been scanned numerically and showed a possibility of SSFS beyond 4 μm and of DW generation beyond 5 μm. We have also studied and prepared tungstate-tellurite glasses and preforms that are highly stable against crystallization, exhibit extremely low level of hydroxyl groups absorption, and from which the suspended-core two-ZDW fibers can be manufactured.

Spectroscopic and laser properties of Ho3+ doped lanthanum‐tungsten‐tellurite glass and fiber

The spectroscopic properties of 2-μm emission in Ho3+-doped lanthanum–tungsten–tellurite glasses with different Ho2O3 concentrations were investigated. The strongest emission was observed in a glass sample doped with 0.5mol% Ho2O3, with a fluorescence lifetime of 3.16ms and a emission cross section of 6.97×10−21cm2 at 2040nm. For this composition, no obvious changes in the emission properties and fluorescence lifetime were observed at temperatures of 295–350K. Using this 60TeO2–30WO3–9.5La2O3–0.5Ho2O3 glass as a core material, Ho3+-doped double cladding fiber with a core diameter of 14μm and a numerical aperture of 0.12 was developed. A maximum laser output power of 34mW at 2040nm was achieved with a 9-cm-long Ho3+-doped tellurite glass fiber. To the best of our knowledge, this study presents the first report on the 2-μm laser output from a Ho3+-doped tellurite oxide glass fiber resonantly pumped by a 1.94μm Tm-fiber laser.

Luminescence spectral studies of Tm3+ ions doped Lead Tungsten Tellurite glasses for visible Red and NIR applications

Lead Tungsten Tellurite (LTT) glasses doped with different concentrations of Tm3+ ions of composition (60−x) TeO2+25WO3+15PbF2+xTm2O3 (Here x=0.1, 0.5, 1.0, 1.5, 2.0, 2.5mol%) were prepared by using melt quenching technique and characterized through optical absorption, photoluminescence and decay spectral studies to know the feasibility of using these glasses as luminescent devices in visible Red and NIR regions. Judd–Ofelt (J–O) theory has been applied to the optical absorption spectral profiles to calculate the J–O intensity parameters Ωλ (λ=2, 4 and 6) and consecutively used to evaluate various radiative properties such as radiative transition probability (AR), radiative lifetimes (τR) and branching ratios (βR) for the prominent luminescent levels. The luminescence spectra for all the LTT glass samples have two intense peaks in bright red and near Infrared regions at 650nm (1G4→3F4) and 800nm (3H4→3H6) respectively for which effective band widths (ΔλP), experimental branching ratios (βexp) and stimulated emission cross-sections (σse) are evaluated. The decay profiles for all the glasses are recorded to measure the quantum efficiency by coupling the radiative with experimental lifetimes. From the measured emission cross-sections, quantum efficiency and CIE chromaticity co-ordinates, it was found that 0.5mol% of Tm3+ ions doped LTT glass is most suitable for generating bright visible Red and NIR lasers to operate at 650 and 800nm respectively.

Plasmon-photon conversion to near-infrared emission from Yb(3+): (Au/Ag-nanoparticles) in tungsten-tellurite glasses.

This manuscript reports on the interaction between 2F5/2→2F7/2 radiative transition from Yb3+ ions and localized surface plasmon resonance (from gold/silver nanoparticles) in a tungsten-tellurite glass. Such an interaction, similar to the down-conversion process, results in the Yb3+ emission in the near-infrared region via resonant and non-resonant energy transfers. We associated such effects with the dynamic coupling described by the variations generated by the Hamiltonian HDC in either the oscillator strength, or the local crystal field, i.e. the line shape changes in the emission band. Here, the Yb3+ ions emission is achieved through plasmon-photon coupling, observable as an enhancement or quenching in the luminescence spectra. Metallic nanoparticles have light-collecting capability in the visible spectrum and can accumulate almost all the photon energy on a nanoscale, which enable the excitation and emission of the Yb3+ ions in the near-infrared region. This plasmon-photon conversion was evaluated from the cavity’s quality factor (Q) and the coupling (g) between the nanoparticles and the Yb3+ ions. We have found samples of low-quality cavities and strong coupling between the nanoparticles and the Yb3+ ions. Our research can be extended towards the understanding of new plasmon-photon converters obtained from interactions between rare-earth ions and localized surface plasmon resonance.

Photon downshifting in strong NIR emitting Er 3+ –Yb 3+ embedded tungsten tellurite glass

Abstract Downshifting/quantum cutting behaviour of the Er3+–Yb3+ doped tungsten tellurite glasses, synthesized by a conventional melt-quenching route is discussed. The non-crystalline nature and thermal stability of the prepared glasses were confirmed by X-ray diffraction, scanning electron microscopy and thermo-gravimetric analysis/differential thermal analysis whereas the optical spectroscopy was obtained via optical absorption and photoluminescence excitation/emission spectra. The results displayed a markable reduction in visible emissions observed through the 2H11/2 → 4I15/2, 4S3/2 → 4I15/2, 4F9/2 → 4I15/2 and 4I9/2 → 4I15/2 transitions of the Er3+ ion and a huge enhancement of about 14.2 times in the near-infrared (∼977 nm upon 490 nm and 325 nm excitations) emission range on incorporation of the Yb3+ ions. A cross relaxation from 4F7/2 → 4I11/2 (Er3+) to 2F7/2 → 2F5/2 (Yb3+) and energy transfer from 4I11/2 (Er3+) to 2F5/2 (Yb3+) states were found to be responsible to cut the blue photon (∼490 nm) into two near infrared (∼977 nm) photons, which put forward the convenience of the present glass as a possible luminescent layer to enhance the efficiency of silicon solar cells.

Spectroscopic properties of Nd3+-doped tungsten–tellurite glasses

In this work, we investigate the spectroscopy properties of neodymium doped tungsten–tellurite glasses prepared in ambient and O2-rich atmospheres. A conversion of TeO4 to TeO3 units was caused by the addition of Nd3+ into the glass, which was confirmed by absorption spectra and by Judd–Ofelt parameter behavior. The relaxation of the 4F3/2 level is dominated by radiative decay and cross-relaxation between Nd3+ and Nd3+ ions. The energy transfer from Nd3+ to the hydroxyl group is negligible when compared to the cross-relaxation. The luminescence quantum efficiency values of the 4F3/2 level decreases as the Nd3+ concentration increases, independently if determined by the Judd–Ofelt method or by the thermal lens technique. The observed reduction in the IR absorption associated to OH groups was not effective to improve the luminescence quantum efficiency.

Blue–green cooperative upconverted luminescence and radiative energy transfer in Yb3+-doped tungsten tellurite glass

Ytterbium-doped tungsten tellurite glasses have been prepared and studied their cooperative upconverted luminescence and radiative energy transfer properties. In a 3.0mol% Yb2O3-doped glass, near-infrared emission band is peaked at around 977nm with a full width at half maximum of around 15nm. This glass emits blue–green upconverted emission under 980nm excitation due to cooperative processes involving two interacting Yb3+ ions. The upconverted emission band is centered at around 502nm with a bandwidth of around 45nm. Power dependence of cooperative emission intensity and the temporal evolutions of the near-infrared and blue–green emissions confirm the presence of cooperative luminescence. Photoluminescence and lifetimes have been measured by moving the laser excitation from one edge of the sample and found that radiative energy transfer is predominant in 3.0mol% of Yb2O3-doped glass. The absorption coefficient obtained from absorption spectrum is in good agreement with that obtained by fitting the curve of luminescence intensity versus distance from the edge of the sample.

Holmium doped Lead Tungsten Tellurite glasses for green luminescent applications

Lead Tungsten Tellurite (LTT) glasses doped with different concentrations of Ho3+ ions have been synthesized using the melt quenching method and characterized to understand their visible emission characteristic features using optical absorption and photoluminescence spectral studies. The Judd–Ofelt (JO) parameters measured from the absorption spectral features were used to evaluate radiative properties such as transition probability (AR), branching ratio (βR) and radiative lifetimes (τR) for the prominent fluorescent levels of Ho3+ ions in LTT glasses. The photoluminescence spectra recorded for all the Ho3+ doped LTT glasses at an excitation wavelength 452nm gives three prominent emission transitions 5F4→5I8, 5F5→5I8 and 5F4→5I7, of which 5F4→5I8 observed in visible green region (546nm) is relatively more intense than the other two transitions. The intensity of 5F4→5I8 emission transition in these glasses increases up to 1mol% of Ho3+ ions and beyond concentration quenching is observed. Branching ratios (βR) and emission cross-sections (σse) were evaluated for the intense emission transition 5F4→5I8 in these glasses to understand the luminescence efficiency in visible green region (546nm). The CIE chromaticity coordinates were also evaluated in order to understand the suitability of these glasses for visible luminescence. From the measured emission cross-sections and CIE coordinates, it was found that 1mol% of Ho3+ ions in LTT glasses are most suitable for visible green luminescence in principle.

Broadband Near-Infrared Luminescence and Visible Upconversion of Er<SUP>3+</SUP>-Doped Tungstate-Tellurite Glasses

Broadband Near-Infrared Luminescence and Visible Upconversion of Er<SUP>3+</SUP>-Doped Tungstate-Tellurite Glasses

Spectroscopic studies of Nd3+ doped lead tungsten tellurite glasses for the NIR emission at 1062 nm

Lead Tungsten Tellurite (LTT) glasses doped with different concentrations of Nd3+ ions were prepared by using the melt quenching technique to study the absorption, emission and decay spectral profiles with an aim to understand the lasing potentialities of these glasses. From the absorption spectra, the Judd–Ofelt (J–O) parameters are evaluated and in turn used to calculate the transition probability (AR), total transition probability (AT), radiative lifetime (τR) and branching ratios (βR) for prominent emission levels of Nd3+. The emission spectra recorded for LTT glasses gives three emission transitions 4F3/2→4I9/2, 4F3/2→4I11/2 and 4F3/2→4I13/2 for which effective band widths (ΔλP) and stimulated emission cross-sections (σse) are evaluated. Branching ratios (βR) measured for all the LTT glasses show that 4F3/2→4I11/2 transition is quite suitable for lasingapplications. The intensity of emission spectra increases with increase in the concentrations of Nd3+ up to 1.0mol% and beyond concentration quenching is observed. Relatively higher emission cross-sections and branching ratios observed for the present LTT glasses over the reported glasses suggests the feasibility of using LTT glasses for infrared laser applications. From the absorption, emission and decay spectral measurements, it was found that 1.0mol% of Nd3+ ion concentration is aptly suitable for LTT glasses to give a strong NIR laser emission at 1062nm.

Enhanced 1.8 μm emission in Yb3+/Tm3+ codoped tungsten tellurite glasses for a diode-pump 2.0 μm laser

Enhanced 1.8μm emission from Tm3+ by Yb3+ sensitization and bubbling in tungsten tellurite glasses has been demonstrated under the excitation of a 976nm laser diode. Radiative properties such as spontaneous emission probabilities, radiative lifetimes and fluorescence branching ratios along with absorption and emission cross sections have been calculated from the absorption spectra. The influences of Yb3+ concentration, Tm3+ concentration, and bubbling time on spectroscopic properties have been thoroughly investigated. It is found that with increasing the bubbling time to 35min, OH− content deceases sharply while 1.8μm emission intensity improves greatly and 3F4 level lifetime prolongs to 1.57ms close to radiative time. After 35min, they change very little due to almost reaching the dynamic balance. The strength of interaction between Tm3+ and OH− is determined. The energy transfer mechanism between Yb3+ and Tm3+ is proposed by photoemission spectroscopy and lifetime measurement. The energy transfer coefficients have been analyzed by the extended spectral overlap method and hopping model. Large ratio of the forward energy transfer from Yb3+ to Tm3+ to the backward one (223) and high energy transfer efficiency (97%) from Yb3+ to Tm3+ ensure efficient 1.8μm emission. Hence, Yb3+ sensitization and the reduction of OH− content could be expected to open up a possibility to achieve high efficient 2.0μm lasing from Tm3+ under a 976nm LD pump.

Enhanced upconversion and temperature sensing study of Er3+–Yb3+ codoped tungsten–tellurite glass

This article reports on the visible upconversion and temperature sensing behaviour of Er3+–Yb3+ doped/codoped TeO2–WO3 glasses prepared by a melting and quenching method. The upconversion emissions have been observed throughout the visible and infrared region upon 980nm and 808nm excitations and assigned suitably from different transitions of the Er3+ ion. The emission intensities of the most intense green band have been enhanced on the co-doping with theYb3+ ions with about 5.92 and 3.99 times upon 980 and 808nm excitations, respectively. The reason behind this improvement is explained on the basis of a power dependence study and an energy level structure. The colour tunability behaviour of the codoped glass has also been investigated upon both excitations. The temperature sensing performance of the prepared glass has been studied by using the fluorescence intensity ratio technique up to 745K. The results suggested that the present glass is a suitable candidate for making a high temperature sensor up to 690K with a sensitivity of about 28.72×10−4K−1.

Pr3+ doped lead tungsten tellurite glasses for visible red lasers

Lead tungsten tellurite (LTT) glasses doped with Pr3+ (0.01, 0.1, 0.5, 1.0 and 1.5mol%) ions were prepared by the conventional melt quenching technique. The glasses were characterized by X-ray diffraction, optical absorption and photoluminescence spectra. The glassy nature of LTT host glass has been confirmed through XRD measurements. From the measured intensities of various absorption bands of these glasses, the three phenomenological Judd–Ofelt (J–O) intensity parameters (Ω2, Ω4 and Ω6) have been evaluated by using the standard as well as modified J–O theory. The J–O parameters measured from the modified J–O theory were used to characterize the absorption and luminescence spectra of these glasses. From this theory, various radiative properties like radiative transition probability (AR), total transition probability (AT), branching ratio (βR) and radiative lifetime (τR) have been evaluated for the fluorescent levels of Pr3+ in these glasses. The emission spectra show five emission bands in visible region for which the effective band widths (ΔλP) and emission cross-sections (σse) have been evaluated. Among all the five emission transitions, a transition 3P0→3F2 is more intense and falls in red region. The visible emission spectra, stimulated emission cross-sections and branching ratios observed for all these glasses suggest the feasibility of using these glasses as lasers in red region. The CIE chromaticity co-ordinates were also evaluated from the emission spectra to understand the suitability of these materials for red emission. From the absorption, emission and CIE chromaticity measurements, it was found that 1mol% of Pr3+ ion concentration is quite suitable for LTT glasses to develop bright red lasers from these glasses.

Enhanced 2.0 μm emission from Ho3+ bridged by Yb3+ in Nd3+/Yb3+/Ho3+ triply doped tungsten tellurite glasses for a diode-pump 2.0 μm laser

Enhanced 2.0 μm emission from Ho3+ bridged by Yb3+ in Nd3+/Yb3+/Ho3+ triply doped tungsten tellurite glasses has been demonstrated upon excitation with an 808 nm laser diode. Nd3+ with high absorption cross section near 808 nm plays an important role in 2.0 μm emission by transferring pump energy to Ho3+:5I5 level. The introduction of Yb3+ could greatly enhance the 2.0 μm emission. The energy transfer efficiency from Nd3+ to Ho3+ and Yb3+ increases from 36.4% to 89.5% with the addition of 5 mol. % Yb2O3, and the energy transfer coefficient from Nd3+ to Yb3+ (29.65 × 10−40 cm6/s) is larger than that from Nd3+ to Ho3+ (3.87 × 10−40 cm6/s). The underlying mechanism is analyzed by means of photoemission spectroscopy and lifetime measurement. The combination of Nd3+/Yb3+/Ho3+ could open up a possibility to realize high efficient 2.0 μm lasing from Ho3+, which could operate at an 808 nm diode laser pump.

Compact broadband amplified spontaneous emission in Tm^3+-doped tungsten tellurite glass double-cladding single-mode fiber

We reported the ~2 μm amplified spontaneous emission (ASE) performance of highly Tm3+-doped (3.76 × 1020 ions/cm3) tungsten tellurite single-mode fibers. The double-cladding fiber was pumped by a commercial 792 nm laser diode without any reflectors. Broadband ASE spectra with the bandwidth (FWHM) varying from ~45 nm to ~140 nm were achieved in a fiber length of 34 cm. The maximum output power was ~34 mW, with a slope efficiency of 4.8%. The ASE beam quality factor (M2) was 1.8. The dependence of output power, ASE mean wavelength, and bandwidth on the launched pump power and fiber length were discussed in detail.