Co-doped Germanate Glass Research Articles

Broadband conversion of ultraviolet to visible and near-infrared emission in Gd3 +/Yb3 + codoped germanate glass

Gd3+/Yb3+ co-doped germanate glasses were fabricated using the melt-quenching method. Broadband visible emission was observed from the gadolinium doped germanate glasses under ultraviolet (UV) excitation, and white-light was obtained by modifying Yb3+ co-dopant concentration. Through this co-doped system, the white-light emission can be further converted into the near-infrared range which is matched well with the energy band gap of commercial silicon solar cell. The possible energy transfer processes involved are proposed and discussed according to the excitation, emission and fluorescence decay measurements. The effect of Yb3+ ion concentration with respect to fixed Gd3+ ions on the visible and near-infrared (NIR) emission has also been studied. The conversion efficiency from visible to near-infrared is as high as 69.3% in the GZN: 0.2Gd2O3–0.6Yb2O3 sample. The results indicate that this material is potential in various applications, such as white LED, enhancing silicon solar cell efficiency, and so on.

Investigation of energy transfer mechanisms between Bi2+ and Tm3+ by time-resolved spectrum

Here, we report for the first time the optical properties of Bi2+ and Tm3+ co-doped germanate glasses and elucidate the potential of this material as substrates to improve the performance of CdTe solar cell. A strong emission peak at 800nm is observed under the excitation of 450–700nm in this material. The energy transfer processes from the transitions of Bi2+ [2P3/2(1)→2P1/2]: Tm3+ [3H6→3H4] are investigated by time-resolved luminescence spectroscopy. A cover glass exhibiting an ultra-broadband response spectrum covering the entire solar visible wavelength region is suggested to enhance the conversion efficiency of CdTe solar cells significantly.

Enhanced light emission near 2.7 μm from Er–Nd co-doped germanate glass

Laser glass gain medium that can convert low cost 808nm diode laser into 2.7μm has attracted considerable interest due to its potential application for medical surgery fiber laser system. In this study, enhanced 2.7μm emission has been achieved in Er3+:germanate glass by co-doping with Nd3+ ions under the excitation of an 808nm diode laser. In the co-doped sample, the experimental results show that the harmful visible emissions via up-conversion were effectively restricted. The reduction of 1.5μm emission was also detected in the co-doped sample, which indicates significant de-excitation of 4I13/2 Er3+ ion through energy transfer and non-radiative decay in Nd3+ ions. In conclusion, the 2.7μm emission enhancement achieved was due to the increased optical absorption of 808nm, efficient energy transfer (ET) with efficiency of 81.73% between Er3+ and Nd3+ ions, and shortening the lifetime of the lower lasing level 4I13/2 Er3+ in the co-doped sample. Therefore, Er3+/Nd3+ co-doped germanate glass could be used to fabricate fiber optical gain media for 2.7μm laser generation.

Emission enhancement in Er3+/Pr3+-codoped germanate glasses and their use as a 2.7-mm laser material

Emission enhancement at 2.7 mm is observed in Er3+/Pr3+-codoped germanate glasses when pumped by a 980-nm laser diode. Significant reductions in 1.5-mm emission and upconversion intensity indicate efficient energy transfer between Er3+ and Pr3+; the energy transfer efficiency is as high as 77.4%. The mechanisms of energy transfer are discussed in detail. The calculated emission cross-section of Er3+/Pr3+-codoped germanate glass is 8.44×10-21 cm2, which suggests that Er3+/Pr3+-codoped germanate glass can be used to achieve efficient 2.7-mm emission.

Comparative Investigation of Optical Properties in Tm<sup>3</sup><sup>+</sup>/Er<sup>3</sup><sup>+</sup>/Yb<sup>3</sup><sup>+</sup> Co-Doped Oxyfluoride Tellurite and Germanate Glasses

Tm3+/Er3+/Yb3+co-doped oxyfluoride tellurite and germanate glasses have been synthesized by conventional melting method. Intense up-conversion (UC) luminescence emissions were simultaneously observed under 980 nm excitation at room temperature in two glasses. The possible UC mechanisms are discussed and estimated. However, in the studied Tm3+/Er3+/Yb3+co-doped oxyfluoride glasses, tellurite glass showed weaker UC emissions than germanate glass, which is inconsistent with the prediction from the difference of maximum phonon energy between oxyfluoride tellurite and germanate glasses. Absorption spectrum and Raman spectroscopy were employed to investigate the origin of the difference in UC luminescence in two glasses. Our results confirm that, besides the maximum phonon energy, the phonon density of host glasses is another important factor in determining the UC efficiency.

Origin of 2.7 μm luminescence and energy transfer process of Er3+: 4I11/2→4I13/2 transition in Er3+/Yb3+ doped germanate glasses

An investigation of spectroscopic property and energy transfer process of Er3+ doped and Er3+/Yb3+ co-doped germanate glasses is presented. The emission cross section of the 4I11/2 → 4I13/2 transition of Er3+ doped germanate glass is calculated to be 1.2 × 10−20 cm2. The microparameter of energy transfer from Yb3+:2 F5/2 to Er3+:4I11/2 is calculated to be 2.74 × 10−39 cm6/s, and that is not phonon dependent in the quasiresonant process. The intensity of the emission around 2.7 μm is enhanced obviously when Er3+ co-doped with Yb3+. The excited-state relaxation process of Er3+ is adequately described by a combination of the Judd-Ofelt model and the energy-gap law. With the exception of 4I13/2 and 4I11/2 levels, multiphonon relaxation is dominant for all excited states, making it possible to efficiently pump the 1.55 μm 4I13/2 → 4I15/2 and 2.7 μm 4I13/2 → 4I11/2 emission by excitation of Yb3+:2F5/2 and Er3+:4I11/2 at 980 nm.

Ultrabroad NIR luminescence and energy transfer in Bi and Er/Bi co-doped germanate glasses

The effects of temperature, pump power and excitation wavelength on near-infrared photoluminescence from Bi-doped multi-component germanate glasses are presented. Compared to conventional silica/silicate matrices, the examined material exhibits superior resistance to thermal quenching and less pronounced excited state absorption for pumping at 808 nm. It is shown that by selecting the optimal excitation wavelength, photoemission can be initiated from multiple active centers in parallel, resulting in an emission bandwidth (full width at half maximum) of more than 370 nm. Er3+/Bi co-doping is presented as an effective means to significantly enhance emission intensity around 1.5 μm by suppressing the typical Er3+-related red-to-green upconversion. Besides its relevance for Bi-doped materials, this also indicates a new route towards improving the performance of Er-based optical devices. The mechanism of Er3+→Bi energy transfer is examined in detail. Adjusting the molar ratio between both species provides an effective tool for tuning the emission scheme and further increasing emission bandwidth.

Radiative Transition Properties of Tm<sup>3+</sup> in Aluminum Germanate Glass for FWW Waveguide Amplifier

Dominant 794nm wavelength upconversion emission, which originates from the Tm3+: 3H4®3H6 transition, has been recorded in Tm3+/Yb3+ codoped aluminum germanate glass under the 974nm wavelength laser excitation. Judd-Ofelt parameters W2 (6.52´10-20cm2), W4 (9.83´10-21cm2) and W6 (1.02´10-20cm2) indicate a higher inversion asymmetric and stronger covalent environment in the glass material. The spontaneous transition probability of 3H4®3H6 was derived to be 1121s-1, which is responsable for obtaining the powerful 794nm emission. K+-Na+ ion-exchanged multimode channel waveguide amplifiers have been fabricated based on the Tm3+/Yb3+ codoped aluminum germanate glass substrate. The relative gain coefficient of a 2.20cm channel waveguide was determined to be 1.58dB/cm at a signal wavelength of 810 nm under 457mW 980nm laser diode excitation.

Gain evaluation of compact designing on Er 3+/Yb 3+ codoped germanate glass channel waveguide

Bent waveguide structures (U- and F-bend) based on UV-sensitive Er 3+/Yb 3+ codoped germanate glass substrates have been designed to achieve high-gain C-band amplification. Using simulated-bend method, the optimal radius for curved structure is offered to be 1.90 cm with loss coefficient of 0.0015 dB/cm, as the substrate size is minimally schemed. In the wavelength range of 1528–1559 nm, obvious gain enhancement for the bent structure waveguides is anticipated, while, for the F-bend waveguide, the internal gain at 1533.8 nm wavelength is derived to be 22.55 dB, which is much higher than the value of 14.06 dB in the U-bend waveguide, and over three times higher than that of the straight one, after compensating both the bend loss and the transition loss. The simulation results indicate that the bent structure designing is beneficial in attaining high optical gain in Er 3+/Yb 3+ codoped germanate glass substrates, which assures that long-period grating can be applied to implement practical C-band gain-flattened amplification.

Enhanced emission of 27 μm pumped by laser diode from Er^3+/Pr^3+-codoped germanate glasses

A novel Er(3+)/Pr(3+) codoped germanate glass was fabricated and analyzed. Efficient emission at 2.7 μm from the glass was observed upon excitation of a conventional 980 nm laser diode. The 2.7 μm emission characteristics and energy transfer (ET) were investigated. Population inversions between ⁴I(13/2) and ⁴I(11/2) levels have been achieved, and an enhanced emission from 2550 to 2800 nm was obtained. Large ET efficiency of 95% indicates that the ET process from Er(3+) to Pr(3+) (⁴I(13/2), ³H₄)→(⁴I(15/2), ³F₃) is efficient and that Pr(3+) can enhance the emission of 2.7 μm by quenching the lower laser level of Er(3+) via ET.

Broadband near-infrared emission from Bi–Er–Tm Co-doped germanate glasses

Bi–Er–Tm co-doped germanate glasses and Bi, Er, Tm singly doped glasses were prepared and characterized through absorption spectra, NIR emission spectra and decay lifetime. A super broadband near-infrared emission from 1000 nm to 1600 nm, covering the whole O, E, S, C, and L bands, was observed in the Bi–Er–Tm co-doped samples due to the result of the overlapping of the Bi related emission band (centered at 1300 nm), the emission from Er 3+ 4I 13/2 → 4I 15/2 transition (centered at 1534 nm) as well as the emission from Tm 3+ 3H 4 → 3F 4 transition (centered at 1440 nm), which is essential for broadly tunable laser sources and broadband optical amplifiers. The energy transfer process was also discussed at the end of the paper.

Spectroscopic properties and energy transfer in Yb 3+–Ho 3+ co-doped germanate glass emitting at 2.0 μm

A new kind of germanate glass co-doped with Yb 3+–Ho3 + was prepared. The J-O parameters were calculated to be Ω 2 = (6.59 ± 0.21) × 10 − 20 cm 2, Ω 4 = (2.77 ± 0.36) × 10 − 20 cm 2, and Ω 6 = (1.90 ± 0.25) × 10 − 20 cm 2. The little overlap between the absorption cross section and stimulated emission cross section indicates a non-resonant energy transfer process. The calculation demonstrates that the energy transfer between Yb 3+ and Ho 3+ is one-phonon assisted in a great measure. The gain coefficient of Ho 3+ at 2.0 μm was also calculated. The fluorescence measurement shows the Yb 3+ co-doping enhances the 2.0 μm emission remarkably.

Investigation on broadband near-infrared emission and energy transfer in Er3+–Tm3+ codoped germanate glasses

Broadband near-infrared emission has been investigated in a new type host composition of Er3+–Tm3+ codoped germanate glass. A broadband emission extend from 1350 to 1675nm with the full width at half maximum (FWHM) around 138nm is obtained in the germanate glass which codoped with 0.2 wt.% Er2O3 and 0.8 wt.% Tm2O3. The energy transfer between Er3+ and Tm3+ plays an important role in the emission mechanism, which is evidenced by the visible upconversion and the lifetime of Er3+:4I13/2 level effected by the addition of Tm2O3. And energy transfer efficiency from Er3+ to Tm3+ reaches 76% for the highest Tm3+ concentration of 0.8 wt.%. These results suggest that this glass would be a promising material for broadband light source and broadband amplifier for the wavelength division multiplexing transmission systems.

2.0 μ m emission properties and energy transfer processes of Yb3+/Ho3+ codoped germanate glass

Ho 3 + doped germanate glass sensitized by Yb3+ has been investigated for potential application as a near-infrared laser material. The characteristic temperatures are determined by differential scanning calorimeter, and the absorption and emission spectra are measured. According to absorption spectra, Judd–Ofelt parameters and radiative transition probabilities are calculated and analyzed by Judd–Ofelt theory. The intensity of emission spectra shows a strong dependence upon the Yb3+ concentration. The result also indicates that Yb3+ plays an important role in the emission of 2.0 μm by transferring the 980 nm excitation energy to Ho3+. The energy transfer process from Yb3+ to Ho3+ is analyzed and the result shows that coefficient of the forward energy transfer Yb3+→Ho3+ is 19 times of magnitude larger than that of the backward energy transfer Yb3+←Ho3+. It is found that the highest gain in 2.0 μm region could be achieved from the germanate glass with 5.0 mol % Yb2O3 and 1.0 mol % Ho2O3. The present Yb3+/Ho3+ codoped germanate glass with high emission cross section of Ho3+:I57→I58 at 2.0 μm and efficient energy transfer from Yb3+ to Ho3+ will be a suitable material for developing solid state lasers around 2.0 μm.

Towards a high-performance optical gain medium based on bismuth and aluminum co-doped germanate glass

In this paper we present the development process of glass based on bismuth and aluminum co-doped germanate (GAB) glass. We found the addition of PbO to this glass (GAPB glass) increased the quantum efficiency (QE). Excitation of GAPB glass at 808 nm produced emission peaking at 1230 nm with a width of 260 nm, indicating the glass may be useful as a broadband optical amplifier covering the second telecommunications window. The composition of each component of the GAPB glass has been optimized for the QE and lifetime of this emission to produce an optimized composition of 87.4GeO2–6Al2O3–6PbO– 0.6Bi2O3 (% molar) which had a QE of 67%. However, this composition had a phase separation tendency which would make the glass unsuitable for fibre fabrication. Next we tried adding various quantities of a variety of glass additives including SiO2, LiO, ZnO and SrCO3. All these additives reduced the QE, and all except SiO2 produced a transparent glass in the appropriate quantity. The quantity of these additives which gave a transparent glass and their QE’s were LiO: 10% and 6%, ZnO: 10% and 43%, SrCO3: 5% and 27%, respectively. Therefore the optimized composition for QE and transparency was 74.4GeO2– 10ZnO–6Al2O3–6PbO–0.6Bi2O3.

NIR luminescence from Er–Yb, Bi–Yb and Bi–Nd codoped germanate glasses for optical amplification

In this paper, we present the near-infrared luminescence from Er–Yb, Bi–Yb, Bi–Nd codoped germanate glasses. Compared with Bi-doped glass, Bi–Yb codoped glass has shown broad infrared luminescence under 800 nm excitation wavelength. The near-infrared spectra of Er 3+–Yb 3+ and Bi and Bi–Yb codoped glasses have shown full width at half maximum (FWHM) around 80 nm, 240 nm and 300 nm, respectively, under 980 nm and 800 nm LD. The absorption band of the Yb 3+ ion was located around 980 nm. Though the absorption band of Yb 3+ does not interact directly with the incident light at 800 nm, near-infrared emission intensity has been highly increased in Bi–Yb codoped glass. We explained the relevant mechanism for the observed enhancement in the near-infrared emission intensity of Bi doped glass with Yb codoping under 800 nm excitation. The measured lifetimes of Bi, Bi–Yb codoped glasses were 490 μs and 815 μs, respectively. The maximum stimulated emission cross sections for 1188 nm and 1258 nm emission bands of Bi and Bi–Yb codoped glasses were 9.003 × 10 −21 cm 2 and 5.445 × 10 −21 cm 2. These Er 3+–Yb 3+, Bi–Yb and Bi–Nd codoped glasses are promising materials for broadly tunable laser sources and broadband optical amplifiers.

Energy transfer processes in (Er 3+–Yb 3+)-codoped germanate glasses for mid-infrared and up-conversion applications

Luminescence characteristics of Er 3+-activated, Yb 3+-sensitised GeO 2–Na 2O–Nb 2O 5 heavy metal germanate glasses have been investigated in the context of searching active media for laser devices. Optical absorption, emission spectra and decay time measurements have been performed at room temperature on these materials. Intense 1540 nm infrared fluorescence and visible emission bands at 533, 554, and 660 nm were observed under continuous wave excitation at 980 nm. An efficient energy transfer from Yb 3+ to Er 3+ ions, increasing as a function of Yb 3+ concentration, favours the Er 3+ 1.54 μm eye-safe laser emission in these materials. The power dependence study of the upconverted emissions gives evidence of a bi-photonic process. Moreover, the Yb 3+ codoping enhances the up-conversion efficiency. Decay time measurements have been examined in the purpose of elucidating the possible mechanisms involved in this process. The experimental results are in good agreement with an effective Yb 3+-to-Er 3+ nonradiative energy transfer.

Effect of PbCl2 addition on structure, OH− content, and upconversion luminescence in Yb3+/Er3+-codoped germanate glasses

Yb3+/Er3+-codoped oxychloride germanate glasses have been synthesized by a conventional melting and quenching method. Structural properties were obtained based on Raman-spectra investigation, indicating that PbCl2 plays an important role in the formation of the glass network and has an important influence on the phonon density and the maximum phonon energy. The Judd–Ofelt intensity parameters and quantum efficiencies were calculated based on the Judd–Ofelt theory and lifetime measurements. The enhanced upconversion luminescence intensity of Er3+ with increasing PbCl2 content could not be explained only by the maximum phonon-energy change of the host glasses. For the first time, the effect of PbCl2 addition on phonon density, OH− content, and upconversion luminescence in oxychloride glasses has been discussed and evaluated. The results show that the effect of phonon density and OH− content on upconversion luminescence in oxychloride glasses is much stronger than that of the decrease of the maximum phonon energy. The possible upconversion luminescence mechanisms have also been estimated and are discussed.

Infrared-to-visible upconversion luminescence of Er3+ and Yb3+ co-doped germanate glass

Frequency upconversion into green and red luminescence in Er3+ and Yb3+ co-doped germanate glass pumped with a 978nm diode laser was presented. With increasing the excitation density, the green upconversion emission intensity was enhanced relative to the red one. Based on the emission spectra and the excitation density dependence of the upconversion emission intensity, we attributed the change of the upconversion emission spectra to the enhancement of three-photon excitation process to produce green luminescence with increasing the excitation density. The effects of this three-photon process on the 1.54μm emission were also discussed.

Compositional Dependence of Infrared‐to‐Visible Upconversion in Yb3+‐ and Er3+‐Codoped Germanate, Gallate, and Tellurite Glasses

Upconversion fluorescences of the green 4S3/2→4I15/2 and red 4F9/2→4I15/2 transitions of the Er3+ ion are studied for Yb3+‐ and Er3+‐codoped sodium germanate, potassium tantalum gallate, and barium tellurite glasses by InGaAs laser‐diode pumping. The phonon energies of the host glasses are determined by infrared‐reflection measurements. Compositional effects on the Judd—;Ofelt parameters for the Er3+ ion, the spontaneous emission probability (SPE) of the 2F5/2→2F7/2 transition for the Yb3+ ion, and the phonon energy of the glass network are discussed in terms of glass structure. The factors that affect the upconversion fluorescence intensities of the Er3+ ion are discussed, using the phonon energy of the host glass and the SPE for the Yb3+ ion in the germanate, gallate, and tellurite glasses.