Single-doped Glasses Research Articles

Effect of Sm-, Gd-codoping on structural modifications in aluminoborosilicate glasses under β-irradiation

Two series of Sm-, Gd-codoped aluminoborosilicate glasses with different total rare earth content have been studied in order to examine the codoping effect on the structural modifications of β-irradiated glasses. The data obtained by electron paramagnetic resonance (EPR) spectroscopy indicated that the relative amount of Gd 3+ ions located in network former positions reveals a non-linear dependence on the Sm/Gd ratio. Besides, codoping leads to the evolution of the EPR signal attributed to defects created by irradiation. The superhyperfine structure of boron oxygen hole centres EPR line becomes less noticeable and less resolved with the increase of Gd. This fact manifests that Gd 3+ ions are mainly diluted in the vicinity of the boron network. By Raman spectroscopy, we showed that the structural changes induced by the irradiation also reveal non-linear behavior with the Sm/Gd ratio. In fact, the shift of the Si–O–Si bending vibration modes has a clear minimum for the samples containing equal amount of Sm and Gd (50:50) in both series of the investigated glasses. In contrast, for single-doped glass there is no influence of dopant’s content on Si–O–Si shift (in the case of Gd) or its diminution (in the case of Sm) occurs, which is explained by the reduction process influence. At the same time, no noticeable effect of codoping on Sm 3+ intensity as well as on Sm 2+ emission or on Sm reduction process was observed.

Enhanced near-infrared emission from Ni2+ in Cr3+∕Ni2+ codoped transparent glass ceramics

Transparent Li2O–Ga2O3–SiO2 glass ceramics containing Cr3+∕Ni2+ codoped LiGa5O8 nanocrystals were synthesized. The steady state emission spectra indicated that the near-infrared emission intensity of Ni2+ at 1300nm in Cr3+∕Ni2+ codoped glass ceramics was enhanced up to about 7.3 times compared with that in Ni2+ single-doped glass ceramics with 532nm excitation. This enhancement in emission intensity was due to efficient energy transfer from Cr3+ to Ni2+, which was confirmed by time-resolved emission spectra. The energy transfer efficiency was estimated to be 85% and the energy transfer mechanism was discussed.

Gain cross-sections of transparent oxyfluoride glass–ceramics single-doped with Ho 3+ (at 2.0 μm) and with Tm 3+ (at 1.8 μm)

We have developed transparent 3.5 mol% Ho 3+ and Tm 3+ single-doped oxyfluoride glass–ceramics, where a large fraction of dopant ions is segregated into PbF 2-based nano-crystals. The absorption and emission cross-sections corresponding to the 5I 7 ↔ 5I 8 transitions of the Ho 3+ (at 2.0 μm), and to the 3H 6 ↔ 3F 4 transitions of the Tm 3+ (at 1.8 μm), have been obtained and respective gain cross-section spectra have been computed as a function of population inversion. For Ho 3+-doped samples, the maximum gain cross-section increased by 20% on ceramming of the precursor glass and reached, for the ensuing glass–ceramics, a value 1.5 times higher than that reported for fluoride glasses. The maximum gain cross-section for Tm 3+-doped samples increased 2.5 times on ceramming of the precursor glasses and reached for the ensuing glass–ceramics a value 2–3 times higher than for other fluoride hosts, such as ZBLAN glass, and 1.5 times higher than for silicate and germanate glass hosts. Hence, these Ho 3+- and Tm 3+-doped glass–ceramics have an advantage for application in planar and fibre lasers/amplifiers at about 2.0, and 1.8 μm, respectively.

Ho 3+: [formula omitted] transition in fluoride glasses

We propose that Ho 3+ and Ho 3+/Yb 3+-doped fluoride glasses are a good candidate material for fiber amplifiers operating at 1340–1400 nm band. Upconversion excitation in the wavelengths of 880–920 and 970–990 nm is achieved for Ho 3+-single-doped glasses, while wavelength region of 910–1000 nm for Ho 3+/Yb 3+-codoped glasses. Ho 3+ concentration is preferably less than 0.5 mol% to avoid lifetime decrease of ( 5 S 2, 5 F 4) manifold. Yb 3+ codoping enhances the upconversion excitation efficiency, however as Yb 3+ concentration increases, back energy transfer from holmium to ytterbium slightly diminishes the fluorescing level lifetime. Some transition-metal ions and rare-earths ions doped in the clad part of a fluoride fiber waveguide, for example, may quench unwanted amplified spontaneous emissions at ∼540 nm and ∼750 nm.