Investigation on Spectral Characteristic and Threshold Behavior of Network Structure of Ge-Sb-S Chalcogenide Glasses.

Two series of chalcogenide glasses in Ge-Sb-S ternary system were synthesized with melt-quenching method. The phycochemical properties and spectral characteristic of glasses with different content of Ge and Sb were obtained with a series of measurements, and the systematic analysis on the change of optical properties was conducted in terms of microstructure of glasses combined with the Raman spectra. With constraint theory based on mean coordination number (Z), we described the variation trend of network structure directly. It was found that as long as the value of Z reaches 2.6, new vibration peaks would be formed in the Raman spectra indicating the presence of threshold behavior as well as the change of the network structure of the Ge-Sb-S glasses which could be expressed in a specific varition in the number of metal bonds and the nonmetal bonds. The appearance of new functional groups in the network have changed the total bond energy of glasses, and then affected the energy band structure of glasses representing the corresponding threshold behavior of the value of optical band gap (Eopg).

Quantum cutting in Pr3+-Yb3+ codoped chalcohalide glasses for high-efficiency c-Si solar cells.

Downconversion materials, which can convert one high-energy photon to two low-energy photons, have provided a promising avenue for the enhancement of solar cell efficiency. In this work, the Pr3+-Yb3+ codoped 25GeS2-35Ga2S3-40CsCl chalcohalide glasses were synthesized in a vacuumed silica ampoule by the melting-quenching technique. Under 474 nm excitation, the visible and near-IR emission spectra reveal the energy transfer from Pr3+ to Yb3+ ions, resulting in the intense 1008 nm near-IR emission for the c-Si solar cells. By tuning the excitation laser power, it is determined that one visible photon has been cut into two near-IR photons during the energy transfer process. With the help of an integrated sphere, the real quantum yields of near-IR emissions were calculated. For the 0.2Pr2S3-0.2Yb2S3 (in mol.%) codoped chalcohalide glass, the quantum yield equals 10.8%. Although this efficiency is still low, this result will open a new route to realize the efficient spectral modification of the solar spectrum.

[Mid-infrared emission properties of Ho3+/Tm(3+)-codoped Ge-Ga-S-CsI glasses].

A serial of chalcogenide glasses based on 78GeS2-12Ga2S3-10CsI (in molar%) system doped with the different radios of Ho3+/Tm3+ ions were synthesized by melt-quenching method. Their absorption spectra and mid-infrared fluorescence under 808 nm laser excitation were measured. According to Judd-Ofelt theory, the intensity parameters omega(i) (i = 2, 4, 6), spontaneous transition probabilities A(rad) and radiative lifetomes tau(r) for Ho3+ ion were calculated. Absorption cross-sections sigma(a), emission cross-sections sigma(e) and gain coefficient G(lambda) corresponding to the emission of Ho3+ ions at 2.0 microm were obtained. By changing the Tm3+ concentration, the energy transfer regime of Tm3+ and Ho3+ ions under 808 nm excitation was investigated. The results show that Ho3+/Tm(3+)-codoped Ge-Ga-S-CsI glasses would be a potential material for 2.0 microm emission.

[Energy transfer and mid-infrared luminescence properties of Tm3+ /Dy3+ codoped chalcohalide glasses].

A series of chalcohalide glasses based on the composition 0.9 (Ge25 Ga5 S70)-0.1CsI doped with the different Tm3+ / Dy3+ ions ratio were synthesized by melt-quenching technique. The absorption spectra, and mid-infrared fluorescence of different glass samples under 800 nm laser excitation were measured. The results prove that, Tm3+ is an efficient sensitizer, which can enhance the Dy3+ : 2.9 microm fluorescence intensity significantly. A decrease in the intensity of 1.8 microm fluorescence and lifetimes of the Tm3+ : (3)F4 level occurred with increasing the concentration of Dy3+ ions from 0 to 1 Wt% where Tm3+ concentration was fixed to 0.5 Wt%. Also a wide spectral overlap between Tm+ : 1.8 microm emission and the absorption of Dy3+ : 6 H(15/2) --> (6)H(11/2) showed that the effective energy transfer between the two rare-earth ions was mainly attributed to the resonance energy from Tm3+: (3)F4 to Dy(3)+ : (6)H(11/2) level.

[Mid-infrared emission and multiphonon relaxation in Tm3+-doped Ge-Ga-Se glasses].

A series of chalcogenide glasses based on the composition Ge30 Ga5 Se65 (at. %) doped with the different Tm3+ ions were synthesized by melt-quenching technique. The refractive indexes, Raman spectra, absorption spectra, near-and mid-infrared fluorescence, and lifetimes of glass samples under 800 nm laser excitation were measured. The intensity parameters omega(i) (i = 2, 4, 6), transition probabilities, branching ratios and radiative lifetimes have been predicted for Tm3+ ions in samples by using the Judd-Ofelt theory. The near-infrared emission spectra at 1.23, 1.48 and 1.8 microm were observed and their quantum efficiencies were evaluated respectively in glass doped with 1 Wt% Tm(3+)-ions under 800 nm excitation. The mid-infrared fluorescence spectra were investigated with the different Tm3+ ion concentration under 800 nm excitation. The multiphonon relaxation rate of Tm3+ : 3 H5 --> 3F4 by the measured and calculated lifetimes, and the relative parameters of W(0) and a in Ge30 Ga5 Se65 glass were evaluated. Results show that the multiphonon relaxation rates were significantly lower than other glasses due to the lower maximum phonon energy, so the selenide glasses are promising as host materials for doping by rare earth ions and for preparation of mid-infrared optical elements.

Study of upconversion fluorescence property of novel Er3+/Yb3+ co-doped tellurite glasses.

Er3+/Yb3+ co-doped TeO2-B2O3-Nb2O5-ZnO (TBN) glasses were prepared. The absorption spectra and upconversion luminescence spectra of TBN glasses were measured and analyzed. The upconversion emission bands centered at 530, 546 and 658 nm were observed under the excitation at 975 nm, corresponding to the transitions of 2H11/2-->4I15/2, 4S3/2-->4I15/2 and 4F9/2-->4I15/2 respectively. The ratio of red emission to green emission increases with an increasing of Yb3+ ions concentration. According to the quadratic dependence on excitation power, the possible upconversion mechanisms and processes were discussed.

[Determination of distribution and effective distribution coefficient of Cr3+ in LiNbO3 single crystals using UV/Visible absorption spectra and ICP].

The LiNbO3 crystals doped with Cr3+ ion (Cr:LN) and co-doped with Cr3+ and Zn ions (Zn:Cr:LN) were grown by the Bridgman method. The absorption coefficient and concentration of Cr3+ in crystals were measured by UV/Visible spectra and inductively coupled plasma (ICP) spectrometry, respectively. The effective distribution coefficients (k) of Cr3+ in the crystals were calculated. The results indicated that the k for Cr:LN crystal decreased from 3.75 to 2.49 as the incorporating concentration of Cr3+ increased from 0.1 to 0.5 mol%; the introduction of ZnO in Cr:LN induced the reduction of k value effectively. However, the k value increased from 1.85 to 2.25 as the incorporating concentration of ZnO increased from 3 to 6 mol%. The variation of the k value was explained by the suppressing effect of ZnO on the incorporation of Cr3+ ions and the distribution of Cr3+ in LN.

Thermal stability, Judd-Ofelt theory analysis and spectroscopic properties of a new Er3+/Yb3+-codoped germano-tellurite glass.

The Er3+/Yb3+-codoped 70TeO2-5Li2O-10B2O3-15GeO2 glass was prepared. The thermal stability, absorption spectra, emission spectra and up-conversion spectra were measured and investigated. The Judd-Ofelt analysis based on absorption spectra was performed in order to determine the Judd-Ofelt intensity parameters Omega(t) (t = 2, 4, 6), spontaneous emission probability, radiative lifetime and branching ratios of several Er3+ transitions. It was found that this studied glass has good thermal stability, broad fluorescence full width at half maximum (FWHM), large stimulated emission cross-section and strong up-conversion emissions at about 532, 546 and 659 nm, corresponding to the 2H(11/2)-->4I(15/2), 4S(3/2)-->4I(15/2) and 4F(9/2)-->4I(15/2) transitions of Er3+, respectively under the excitation at 970 nm. The results suggest that this Er3+/Yb3+-codoped germano-tellurite glass may be a potentially useful material for developing potential amplifiers and up-conversion optical devices.

Investigation of thermal stability and spectroscopic properties in Er3+/Yb3+-codoped TeO2-Li2O-B2O3-GeO2 glasses.

The new Er3+/Yb3+ co-doped 70TeO2-5Li2O-(25-x)B2O3-xGeO2 (x = 0, 5, 10, 15 fand 20 mol.%) glasses were prepared. The thermal stability, absorption spectra, emission spectra and lifetime of the 4I(13/2) level of Er3+ ions were measured and studied. The FT-IR spectra were carried out in order to investigate the structure of local arrangements in glasses. It is found that the thermal stability, absorption cross-section of Yb3+, emission intensity and lifetime of the 4I(13/2) level of Er3+ increase with increasing GeO2 content in the glass composition, while the fluorescence width at half maximum (FWHM) at 1.5 um of Er3+ is about 70 nm. The obtained data suggest that this system glass can be used as a candidate host material for potential broadband optical amplifiers.

Study of luminescence properties of novel Er3+ single-doped and Er3+/Yb3+ co-doped tellurite glasses.

The novel Er(3+) single-doped and Er(3+)/Yb(3+) co-doped tellurite glasses were prepared. The effect of Yb(2)O(3) concentration on absorption spectra, emission spectra and upconversion spectra of glasses were measured and investigated. The emission intensity, fluorescence full width at half maximum (FWHM) and upconversion luminescence of Er(3+) go up with the increasing concentration of Yb(3+) ions. The maximum FWHM of (4)I(13/2) --> (4)I(15/2) transition of Er(3+) is approximate 77 nm for 1.41 x 10(21)ions/cm(3) concentration of Yb(3+)-doped glass. The visible upconversion emissions at about 532, 546 and 659 nm, corresponding to the (2)H(11/2) --> (4)I(15/2), (4)S(3/2) --> (4)I(15/2) and (4)F(9/2) --> (4)I(15/2) transitions of Er(3+), respectively, were simultaneously observed under the excitation at 970 nm. Subsequently, the possible upconversion mechanisms and important role of Yb(3+) on the green and red emissions were discussed and compared. The results demonstrate that this kind of tellurite glass may be a potentially useful material for developing potential amplifiers and upconversion optical devices.