CsBr Glasses Research Articles

Novel Ge–Ga–Te–CsBr glass system with ultrahigh resolvability of halide

CO2 molecule, one of the main molecules to create new life, should be probed accurately to detect the existence of life in exoplanets. The primary signature of CO2 molecule is approximately 15μm, and traditional S- and Se-based glass fibers are unsuitable. Thus, Te-based glass is the only ideal candidate glass for far-infrared detection. In this study, a new kind of Te-based chalcohalide glass system was discovered with relatively stable and large optical band gap. A traditional melt-quenching method was adopted to prepare a series of (Ge15Ga10Te75)100−x (CsBr)x chalcogenide glass samples. Experiment results indicate that the glass-forming ability and thermal properties of glass samples were improved when CsBr was added in the host of Ge–Ga–Te glass. Ge–Ga–Te glass could remarkably dissolve CsBr content as much as 85at.%, which is the highest halide content in all reports for Te-based chalcohalide glasses. Moreover, ΔT values of these glass samples were all above 100°C. The glass sample (Ge15Ga10Te75)65 (CsBr)35 with ΔT of 119°C was the largest, which was 7°C larger than that of Ge15Ga10Te75 host glass. The infrared transmission spectra of these glasses show that the far-infrared cut-off wavelengths of (Ge15Ga10Te75)100−x (CsBr)x chalcogenide glasses were all beyond 25μm. In conclusion, (Ge15Ga10Te75)100−x (CsBr)x chalcogenide glasses are potential materials for far-infrared optical application.

Upconversion Luminescence of Er3+ Doped Chalcohalide Glasses and the Potential Application for Si Solar Cell Efficiency Enhancement

Er doped Ge-Ga-S-CsBr chalcohalide glasses were fabricated by melt-quenching method. The properties of upconversion luminescence under the excitation of 1550 nm laser were investigated. Strong green emissions centered at 525 nm and 545 nm, and weak red emission centered at 660 nm, were observed, along with near infrared emission bands centered at 810 nm and 980 nm. The up-conversion fluorescence was contributed to multi-photon involved process. The Si solar cell efficiency slightly increased from 7.28% (without upconversion layer) to 7.32% (using Er doped 0.9(Ge25Ga10S65)-0.1CsBr glass as upconversion layer). The results show that the investigated Er-doped chalcohalide glasses has a potential application for the enhancement of Si solar cell efficiency.

CsBr decreasing the phonon energy in Dy3+ doped GeGaSe glass

The electron–phonon coupling is firstly investigated in the Dy3+-doped Ge30Ga5Se65 and 0.9Ge30Ga5Se65+0.1CsBr glasses. Using the Judd–Ofelt theory, the intensity parameters, spontaneous emission probabilities and branching ratios of Dy3+ ions are calculated. Measured lifetimes (τm) of 6H11/2 manifold are measured in temperature region of 20–300K. Results show that local phonon modes and electron–phonon (e–p) coupling strengths are changed in the addition of CsBr. The frequency of the phonon vibration was decreased to 268cm−1 with CsBr addition to selenide glasses. The value of e–p coupling strength decreases from 0.456 in Ge30Ga5Se65 to 0.048 in 0.9Ge30Ga5Se65+0.1CsBr. It is clear that the e–p coupling strengths decrease considerably with the addition of CsBr to Ge30Ga5Se65 glass.

Up-conversion fluorescence and low-temperature emission in Er 3+-doped GeGaS–CsBr glasses

Optical properties of Er-doped chalcohalide GeGaS–CsBr glasses have been investigated as a function of Er and Ga concentrations. Nominal compositions of (Ge 0.25Ga. 0.10S 0.65) 0.9(CsBr) 0.1 and (Ge 0.23Ga. 0.12S 0.65) 0.9(CsBr) 0.1 glassy hosts have been chosen for this study. The effects of Er content and host composition on 1.5 μm emission of Er 3+ ions, measured at low-temperature of 20 K under excitation by 514.5 nm, have been specified. Besides, the up-conversion fluorescence of Er 3+ ions pumped at 795 nm is reported. Two intense emission bands in the green and one weak emission band in the red regions around 530, 554 and 644 nm have been observed, and were attributed to 2H 11/2 → 4I 15/2, 4S 3/2 → 4I 15/2, and 4F 9/2 → 4I 15/2 transitions of Er 3+ ions, respectively. The simplified energy-level diagram of Er 3+ ion has been used to identify the observed up-conversion fluorescence bands in visible region.

The influence of CsBr addition on optical and thermal properties of GeGaS glasses doped with erbium

The influence of the addition of CsBr on the optical and thermal properties of GeGaS glass doped with Er has been being investigated. We find that the addition of CsBr into GeGaS glass leads to some improvements in the radiative properties of Er3+ ions in this glass system. The GeGaS–CsBr glasses demonstrate much longer radiative lifetimes and stronger photoluminescence for \(^4\hbox{I}_{13/2} \rightarrow{^4\hbox{I}}_{15/2}\) and \( ^2\hbox{H}_{11/2} \rightarrow{^4\hbox{I}}_{15/2}\) transitions in Er3+ ions. Very low Judd-Ofelt parameters and sharp Er3+ absorption spectra with multiple peaks suggest the presence of microcrystals. All optical parameters are strongly influenced by the interplay of Ga and CsBr. The glasses studied have been characterized by their basic glass transformation temperatures. The addition of CsBr into GeGaS glass keeping the ratio between CsBr and Ga close to unity is favorable for the incorporation of larger amount of Er. The experimental results are discussed in terms of structural local arrangement induced by CsBr addition.

EXAFS investigation on the structural environment of Tm3+ in Ge–Ga–S–CsBr glasses

The local structures around Tm3+ in Ge0.25Ga0.10S0.65 and 0.90 (Ge0.25Ga0.10S0.65)−0.10CsBr glasses were investigated using Extended X-ray absorption fine structure (EXAFS) spectroscopy. In Ge0.25Ga0.10S0.65 glass, Tm3+ ions are surrounded by approximately seven S ions. Addition of 10mol% CsBr resulted in significant changes in the EXAFS spectrum of Tm3+ ions due to the changes in the local structure surrounding Tm3+ ions. The first-nearest coordination shell around Tm3+ ion is predominantly composed of about six Br ions in 0.90 (Ge0.25Ga0.10S0.65)−0.10CsBr glass.

Emission properties and local structure of Tm 3+ in Ge–Ga–S–Br glass

Spectroscopic properties of Tm 3+ in (1 − x) (Ge 0.25Ga 0.10S 0.65)– xBr (or CsBr) glasses ( x = 0.0 and 0.1) were investigated. Emission properties of Tm 3+ in 0.9(Ge 0.25Ga 0.10S 0.65)–0.1Br glass were similar to those in Ge 0.25Ga 0.10S 0.65 glass, while there was significant improvement when doped into 0.9(Ge 0.25Ga 0.10S 0.65)–0.1CsBr glass. The lifetime of the Tm 3+: 3H 4 level increased from 0.23 to 1.22 msec with 10 mol% CsBr addition. The presence of Cs + facilitated the formation of [GaS 3/2Br] − units by donating an electron to the Ga tetrahedron, resulting in the homogeneous distribution of Br. In this way, Tm 3+ ions have their local environment made of Br only. When Br ions were added instead of CsBr, [GaS (4− x)/2 Br] − units with x > 1 were formed and Tm 3+ ions were surrounded by both S and Br, producing a high phonon environment.

Emission and local structure of rare-earth ions in chalcogenide glasses

Local structures of rare-earth ions in Ge–Ga–S–CsBr glasses were investigated to understand the structural origin on the emission property enhancement. The frequency of the phonon vibration controlling the multiphonon relaxation was changed to 245cm−1 due to the formation of Ga–Br bonds with CsBr addition to sulfide glasses. Formation of this new chemical bond was also confirmed from the phonon side band spectra of Eu3+ ions. Analyses of the EXASF spectra proved that Tm3+ ions were surrounded by approximately seven S ions in Ge0.25Ga0.10S0.65 glass but were coordinated by ∼6 Br ions in the glass with 10mol% of CsBr.

Ge and Ga K-edge EXAFS analyses on the structure of Ge–Ga–S–CsBr glasses

The local structure of Ge and Ga ions in (1−x)(Ge0.25Ga0.10S0.65)–xCsBr glasses (x=0.00,0.05,0.10 and 0.12) were investigated using extended X-ray absorption fine structure (EXAFS) spectroscopy. CsBr formed [GaS3/2Br]− structural units in glass while Ge ions remained in GeS4/2 tetrahedra, unaffected by CsBr addition. Rare-earth ions can be surrounded by Br ions only when CsBr/Ga ratio in glass became larger than unity.

1.48 - μ m emission properties and energy transfer between Tm3+ and Ho3+∕Tb3+ in Ge–Ga–As–S–CsBr glasses

Emission properties of Tm3+ in (0.85−x)(Ge0.25As0.10S0.65)–0.15GaS3∕2–xCsBr glass (x=0–0.17) were investigated. With 15mol% CsBr addition, the emission intensity of 1.48-μm increased accompanied by a large increase in the lifetime of the Tm3+:H43 level up to 1.2ms. At the same time, a 1.48-μm emission peak splits into two peaks due to the changes in the local structure surrounding Tm3+ ions. To achieve population inversion in Tm3+ ions, Ho3+ or Tb3+ were codoped into 0.70(Ge0.25As0.10S0.65)–0.15GaS3∕2–0.15CsBr glass. The population of the Tm3+:F43 level was effectively quenched with Ho3+ or Tb3+ codoping. Critical distances of Tm3+:F43→Ho3+:I75 and Tm3+:F43:→Tb3+:F0,1,27 energy transfer were 9.1 and 12.7Å, respectively. The population density differences were higher with Ho3+ codoping than with Tb3+ due to the crossrelaxation of Tm3+:H43→H53 to Tb3+:F67→F37.

Rare-earth doped chalcogenide glasses for fiber-optic amplifiers

Emission properties associated with the fiber-optic amplification in Ge–Ga–S–CsBr glasses were investigated. The intensity of the 1.31 μm emission from Dy3+ (6F11/2·6H9/2→6H15/2) increased sharply when the appropriate concentrations of alkali halides were added, at the expense of the 1.75 μm emission intensity (6H11/2→6H15/2). The lifetimes of the 1.31 μm emission level also increased up to 1580 μs. A small amount of As was added to increase the resistivity against the recrystallization during re-heating. The optimum composition for practical usage was 0.7[Ge0.25As0.10S0.65]–0.15GaS3/2–0.15CsBr. Phonon side band showed that the several local phonon modes, with the frequencies around 100 cm−1, were coupled to 4f electrons of Eu3+. The nearest neighbors of Eu3+ ions are composed of halogen ions that are part of well-structured complex such as tetrahedral [GaS3/2Br]− subunit and/or Ga2Br6.

1.48 μm emission properties and the cross-relaxation mechanism in chalcohalide glass doped with Tm 3+

1.48 μm emission properties and the cross-relaxation mechanism of Tm 3+ ions in 0.7(Ge 0.25As 0.10S 0.65) + 0.15GaS 3/2 + 0.15CsBr glass were investigated. Both the relative intensity ratio of the 1.48 μm emission to 1.82 μm and the measured lifetime of the 3H 4 level decreased with increasing Tm 3+ concentration. When temperature decreased from room temperature to 20 K, lifetimes of the 3H 4 level increased from 670 to 970 μs. At the same time, the critical distance for cross-relaxation decreased from 1.11 to 0.93 nm. These results indicate that cross-relaxation ( 3H 4, 3H 6 → 3F 4, 3F 4) became less effective as temperature decreased. Analysis of the temperature dependence of cross-relaxation rates showed that cross-relaxation in Tm 3+ is a phonon-assisted energy transfer process. The major phonon contributing to the process is from the Ga–Br vibration in [GaS 3/2Br] − units.

Optimization of Dy [formula omitted]-doped Ge–Ga–As–S–CsBr glass composition and its 1.31 μm emission properties

An optimum glass composition for practical fiber fabrication was investigated for Ge–Ga–As–S–CsBr glasses. Dy 3+ was doped into the glasses and its emission properties were examined. The best composition for practical use was 0.7[Ge 0.25As 0.1S 0.65]–0.15GaS 3/2–0.15CsBr. This glass also exhibited high resistance against the attack of liquid water. The lifetime and quantum efficiency of the 1.31 μm emission from Dy 3+ increased approximately 17 and 4 times, respectively, compared to those obtained from other sulfide glasses. This is due to the formation of [GaS 3/2Br] − units. The frequency of the effective phonon which dominates the multiphonon relaxation process decreased from 375 to 245 cm −1 with the addition of CsBr.

Enhancement of the 1.31-μm emission properties of Dy3+-doped Ge–Ga–S glasses with the addition of alkali halides

Alkali halides such as KBr, KI, CsBr, and CsI were added to Dy3+-doped Ge–Ga–S glasses, and their effects on the 1.31-μm emission property were investigated. The intensities of the 1.31-μm emission (6F11/2 · 6H9/2 → 6H15/2) increased at the expense of the 1.75-μm emission intensity (6H11/2 → 6H15/2) with the alkali halide addition. The lifetimes of the 1.31-μm emission level also increased as much as 35 times from 38 μs for Ge–Ga–S glass to 1320 μs for the glass containing 10 mol% CsBr. These enhancements occurred only when the ratio of MX (M = K, Cs; X = Br, I)/Ga was equal to or larger than unity. Raman spectra of Ge–Ga–S–CsBr glasses indicated the formation of [GaS3/2Br]− complexes, which provide the preferred sites for Dy3+. Due to this new local environment of Dy3+, the multiphonon relaxation rates from the Dy3+:6F11/2 · 6H9/2 level decreased by approximately four orders of magnitude. The enhancement in the 1.31-μm emission properties with alkali halide addition supports the potentials of these glasses as hosts for the Dy3+-doped fiber-optic amplifiers.