Spectroscopic study of optical centers formed in Bi-, Pb-, Sb-, Sn-, Te-, and In-doped germanate glasses

Structure and magnetic properties of Bi-doped calcium aluminosilicate glass microspheres

Bi-doped CaO–Al2O3–SiO2 glass microspheres with Ca2Al2SiO7 (gehlenite) composition were prepared by combination of solid-state reaction and flame synthesis. The concentration of Bi was 0.0, 0.5, 1 and 3 mol %. The chemical composition of prepared glass microspheres was determined by X-ray fluorescence (XRF). The structural and magnetic properties of prepared glass microspheres and their polycrystalline analogues were studied by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Raman spectroscopy and SQUID magnetometry. The closer inspection of glass microspheres surface by SEM confirmed smooth surface and revealed no features indicating presence of crystalline phases. All Bi-doped microspheres are X-ray amorphous, however in case of undoped microspheres XRD detected traces of crystalline gehlenite. XRD analysis of samples crystallized at 1273 K for 10 h revealed the presence of gehlenite as the main crystalline phase. The presence of gehlenite in crystallized samples were also confirmed by Raman spectroscopy. All samples (glass microspheres and their crystalline analogues) showed diamagnetic or weak ferromagnetic behavior at room temperature, whereas paramagnetic or weak ferromagnetic behavior was observed at 2 K.

Ultra-wideband and flat-gain optical properties of the PbS quantum dots-doped silica fiber

We investigate the microstructural characteristics and optical properties of PbS quantum dots-doped silica fiber (PQDF), prepared by atomic layer deposition (ALD) doping technique. The fiber exhibits ultra-wideband luminescence and flat-gain with 3 dB bandwidth of 300 nm. The on-off gain and net gain can reach to 7.1-15.0 dB and 6.0-9.2 dB at 1050-1350 nm, respectively. The results of high-resolution transmission electron microscopy (HRTEM) further reveal the effects of PbS QDs doping in PQDF. The broadband luminescence spectrum originating from three active centers (1086, 1179, and 1304 nm), can be attributed to the dimension effect of PbS QDs (3.7, 4.0, and 4.3 nm, respectively). Moreover, the calculation results indicate that the multi-sized PbS QDs concentrated at 3.65-4.45 nm make the 3 dB gain bandwidth increase, which is six times wider than that of traditional erbium-doped fiber (EDF). Therefore, this type of PQDF is a promising gain medium for optical amplifiers and broadband light sources.

Photoluminescence in Ga/Bi co-doped silica glass

Bismuth-Gallium co-doped silica glass fiber preform was prepared from nano-porous silica xerogels using a conventional solution doping technique with a heterotrinuclear complex and subsequent sintering. Ga-connected optical Bismuth active center (BAC) was identified as the analogue of Al-connected BAC. Visible and infrared photoluminescence (PL) were investigated in a wide temperature range of 1.46 - 300 K. Based on the results of the continuous wave (CW) and time resolved (TR) spectroscopy we identify the centers emitting in the spectral region of 480 - 820 nm as Bi(+) ions. The near infrared (NIR) PL around 1100 nm consists of two bands. While the first one can be ascribed to the transition in Bi(+) ion, the second band is presumably associated to defects. We put in evidence the energy transfer (ET) between Bi(+) ions and the second NIR emitting center via quadrupole-quadrupole and dipole-quadrupole mechanisms of interactions. Finally, we propose the energy level diagram of Bi(+) ion interacting with this defect.

Intense near-infrared emission of 1.23 μm in erbium-doped low-phonon-energy fluorotellurite glass

Intense near-infrared emission located at 1.23 μm wavelength originating from the erbium (Er(3+)):(4)S3/2→(4)I11/2 transition is observed in Er(3+)-doped fluorotellurite glasses. This emission is mainly contributed by the relatively low phonon energy of the fluorotellurite glass host (~776 cm(-1)). Judd-Ofelt analysis indicates a strong asymmetry and covalent environment between Er(3+) ions and ligands in the host matrix. The emission cross-section was calculated to be 2.85×10(-21) cm(2) by the Füchtbauer-Ladenburg equation, and the population inversion is realized according to a simplified evaluation. The results suggest that the fluorotellurite glass system could be a promising candidate for the development of optical amplifiers and lasers operating at the relatively unexplored 1.2 μm wavelength region.

On the analogy between photoluminescence and carrier-type reversal in Bi- and Pb-doped glasses

Reaction order in Bi-doped oxide glasses depends on the optical basicity of the glass host. Red and NIR photoluminescence (PL) bands result from Bi(2+) and Bin clusters, respectively. Very similar centers are present in Bi- and Pb-doped oxide and chalcogenide glasses. Bi-implanted and Bi melt-doped chalcogenide glasses display new PL bands, indicating that new Bi centers are formed. Bi-related PL bands have been observed in glasses with very similar compositions to those in which carrier-type reversal has been observed, indicating that these phenomena are related to the same Bi centers, which we suggest are interstitial Bi(2+) and Bi clusters.

Superbroadband near-infrared emission and energy transfer in Pr3+-Er3+ codoped fluorotellurite glasses

We report the first demonstration of superbroadband emission extending from 1.30 to 1.68 μm in praseodymium(Pr(3+))-erbium(Er(3+)) codoped fluorotellurite glasses under 488 nm excitation. This superbroad near-infrared emission is contributed by the Pr(3+): (1)D(2)→(1)G(4) and Er(3+): (4)I(13/2)→(4)I(15/2) transitions which lead to emissions located at 1.48 and 1.53 μm, respectively. The quenching of the Pr(3+) emission resulted from the cross relaxation [(1)D(2), (3)H(4)]→[(1)G(4), (3)F(3,4)] was effectively compensated by the codoping of Er(3+). The results suggest that, other than the heavy-metal and transition-metal elements of active bismuth (Bi), nickel (Ni), chromium (Cr), etc., Pr(3+)-Er(3+) codoped system is a promising alternative for the broadband near-infrared emission covering the expanded low-loss window.

Superbroadband near-IR photoluminescence from Pr3+-doped fluorotellurite glasses

Praseodymium(Pr3+)-doped fluorotellurite glasses were synthesized and broadband photoluminescence (PL) covering a wavelength range from 1.30 to 1.67 μm was observed under both 488 and 590 nm wavelength excitations. The broadband PL emission is mainly due to the radiative transition from the manifolds Pr3+: 1D2 to 1G4. The PL line-shape, band width, and lifetime were modified by the Pr3+ dopant concentration, and a quantum efficiency as high as 73.7% was achieved with Pr3+ dopant in a low concentration of 0.05 mol%. The good spectroscopic properties were also predicted by the Judd-Ofelt analysis, which indicates a stronger asymmetry and covalent bonding between the Pr3+ sites and the matrix lifgand field. The large stimulated emission cross-section, long measured lifetime, and broad emission bandwidth confirm the potential of the Pr3+-singly doped fluorotellurite glass as broadband luminescence sources for the broadband near-infrared optical amplifications and tunable lasers.

Near-infrared ultrabroadband luminescence spectra properties of subvalent bismuth in CsI halide crystals

We observed two ultrabroadband near-infrared (NIR) luminescence bands around 1.2 and 1.5 μm in as-grown bismuth-doped CsI halide crystals, without additional aftertreatment. Dependence of the NIR emission properties on the excitation wavelength and measurement temperature was studied. Two kinds of NIR active centers of subvalent bismuth and color centers were demonstrated to coexist in Bi:CsI crystal. The eye-safe 1.5 μm emission band with an FWHM of 140 nm and lifetime of 213 μs at room temperature makes Bi:CsI crystal promising in the applications of the ultrafast laser and ultrabroadband amplifier.

Combined excitation-emission spectroscopy of bismuth active centers in optical fibers

For the first time, 3-dimensional luminescence spectra (luminescence intensity as a function of the excitation and emission wavelengths) have been obtained for bismuth-doped optical fibers of various compositions in a wide spectral range (450-1700 nm). The bismuth-doped fibers investigated have the following core compositions: SiO(2), GeO(2), Al-doped SiO(2), and P-doped SiO(2). The measurements are performed at room and liquid nitrogen temperatures. Based on the experimental results, the positions of the low-lying energy-levels of the IR bismuth active centers in SiO(2)- and GeO(2)-core fibers have been determined. Similarity of the energy-level schemes for the two core compositions has been revealed.

Influence of electron irradiation on optical properties of Bismuth doped silica fibers

We report a study of the attenuation spectra transformations for a series of Bismuth (Bi) doped silica fibers with various contents of emission-active Bi centers, which arise as the result of irradiation by a beam of high-energy electrons. The experimental data reveal a substantial decrease of concentration of the Bi centers, associated with the presence of Germanium in silica glass, at increasing the irradiation dose (the resonant-absorption bleaching effect in germano-silicate fiber). In contrast, the spectral changes that appear in Bi doped alumino-silicate fiber have through irradiation a completely different character, viz., weak growth of the resonant-absorption peaks ascribed to the Bi centers, associated with the presence of Aluminum in silica glass. These results demonstrating high susceptibility of Bi centers to electron irradiation while opposite routes of the irradiation-induced spectral changes in Bi doped germanate and aluminate fibers seem to be of worth notice for understanding the nature of these centers.

Tm3+-doped tellurite glasses for fiber amplifiers in broadband optical communication at 1.20 µm wavelength region

Broadband emissions at around 1.20 and 1.46 μm wavelengths from thulium (Tm(3+))-doped tellurite glasses were observed under 465 nm wavelength excitation. The 1.20 μm emission originates from the Tm(3+): (1)G(4)-->(3)H(4) transition, and the associated stimulated peak emission cross-section is calculated to be 0.47 × 10(-20) cm(2). Population inversion occurs between the (1)G(4) and (3)H(4) levels, and a positive gain band from 1.20 to 1.28 μm is achieved at relatively low Tm(3+) dopant concentration. Our results suggest that this glass system is promising for optical fiber amplifiers operating at the relatively unexplored low loss 1.20 μm wavelength region.

Broadband NIR photoluminescence from Bi-doped Ba2P2O7 crystals: insights into the nature of NIR-emitting Bismuth centers

We report on a novel type of Bi-doped crystal that exhibits ultrabroadband photoluminescence in the near infrared (NIR). Emission centers can be generated and degenerated reversibly by annealing the material in CO atmosphere and air, respectively, indicating that emission is related to the presence of Bi-species in low valence states. Correlating static and dynamic excitation and emission data with the size and charge of available lattice sites suggests that two types of Bi(0)-species, each located on one of the two available Ba(2+) lattice sites, are responsible for NIR photoemission. This is further confirmed by the absence of NIR emission in polycrystalline Ca(2)P(2)O(7):Bi and Sr(2)P(2)O(7):Bi. Excitation is assigned to transitions between the doubly degenerated ground state (4)S(3/2) and the degenerated excited levels (2)D(3/2), (2)D(5/2) and (2)P(1/2), respectively. NIR emission is attributed to (2)D(3/2)?(4)S(3/2). The NIR emission center can coexist with Bi(2+) species. Then, also Bi(2+) is accommodated on one of the two Ba(2+)-sites. Energy transfer between Bi(2+) ions occurs within a critical distance of 25.9 A.

Near-infrared photoluminescence and Raman characterization of bismuth-embedded sodalite nanocrystals

Ultrabroadband near-IR (NIR) emission has been realized in bismuth-embedded sodalite nanocrystals. Steady-state and time-resolved photoluminescence and Raman results suggest that Bi(+) active centers contribute to the NIR emission. This study demonstrates that sodalite nanocrystals can serve as excellent hosts for bismuth NIR active centers, thus paving the way for their wide applications in nanophotonics.

Study on the effect of heat-annealing and irradiation on spectroscopic properties of Bi:alpha-BaB2O4 single crystal

The absorption, excitation, and ultrabroadband near-infrared luminescence spectra of Bismuth were investigated in H(2)-annealed and gamma-irradiated Bi:alpha-BaB(2)O(4)(alpha-BBO) single crystals, respectively. Energy-level diagrams of the near-infrared luminescent centers were fixed. The electronic transition energies of near-infrared active centers are basically consistent with the multiplets of free Bi(+) ions. The minor difference of the energy-level diagrams of Bi(+) ions in H(2)-annealed and gamma-irradiated Bi:alpha-BaB(2)O(4) crystals can be ascribed to the difference of the local lattice environments. The involved physical and chemical processes were discussed. The effect of Ar-, air-annealing and electron-irradiation on Bi:alpha-BaB(2)O(4) crystal were also investigated.

Broadband near-infrared luminescence in gamma-irradiated Bi-doped alpha-BaB(2)O(4) single crystals

Spectroscopic properties of as-grown and gamma-irradiated undoped and Bi-doped alpha-BBO (BaB(2)O(4)) single crystals were investigated. Bi(2+) and color centers in Bi:alpha-BBO crystals were investigated to be nonluminescent in the near-infrared (NIR) region. Broadband NIR luminescence at 1139 nm with a FWHM of 108 nm and a decay time of 526 mus was realized in Bi:alpha-BBO crystal through gamma irradiation. Bi(+) was attributed to be responsible for the NIR emission, which can be bleached by thermal annealing. The involved physical processes in Bi:alpha-BBO crystal during the courses of irradiation and heat annealing were tentatively established.

Luminescence and optical gain in Pb-doped silica-based optical fibers

IR luminescence and optical gain in a Pb-doped fiber have been observed for the first time. Absorption, luminescence and pump on/pump off optical gain spectra, as well as luminescence decay time, have been measured in these fibers. Comparison of optical active center characteristics in Pb-doped and Bi-doped fibers of the same composition indicates an essential difference of optical active centers in these two types of fibers.

Spectroscopic properties and near-infrared broadband luminescence of Bi-doped SrB4O7 glasses and crystalline materials

Spectroscopic properties of Bi-doped SrB(4)O(7) glasses, sintered compounds, polycrystalline materials, and single crystals were investigated. Broadband near-infrared luminescence was realized in Bi-doped SrB(4)O(7) glasses with basicity and polycrystalline materials with non-bridging oxygens. In Bi:SrB(4)O(7) single crystals, only visible luminescence of Bi(3+) and Bi(2+) was observed, but no near-infrared. The rigid three-dimensional network of SrB(4)O(7) crystal is proved to be unfavorable for accommodation of Bi(+) ions.

Molecular orbital model of optical centers in bismuth-doped glasses

Spectroscopic properties of optical fibers with a bismuth-doped silicate glass core are explained on the basis of molecular orbital theory and a solution of the Schrödinger equation, which takes into account the exchange, the spin-orbital, and the glass field potential interactions of s, p, and d electron shells of bismuth with s(sigma), p(sigma), and p(pi) orbits of oxygen atoms. The approach can explain the IR luminescence properties of other optical centers formed by other atoms with the same structure of electron shells as the bismuth atom. The model of transitions based on intramolecular charge transfer between molecular orbital and metallic states is proposed.

Superbroadband near-IR nano-optical source based on bismuth-doped high-silica nanocrystalline zeolites

We have shown that efficient superbroadband near-IR luminescence can be realized in bismuth-doped high-silica nanocrystalline zeolites. The emission band covered the range of 930-1620 nm, with a maximum peak at 1146.3 nm, an FWHM of 152 nm, and a lifetime of over 300 mus under the excitation of a 488 nm laser line. The observed luminescence was attributed to subvalent Bi (Bi(+)) ions formed in the annealed zeolites. These Bi-doped nanozeolites may find applications as superbroadband near-IR nano-optical sources.

Bi-doped BaF2 crystal for broadband near-infrared light source

Bi-doped BaF(2) crystal was grown by the temperature gradient technique and its spectral properties were investigated. The absorption, emission and excitation spectra were measured at room temperature. Two broadband emissions centered at 1070 and 1500 nm were observed in Bi-doped BaF(2) crystal. This extraordinary luminescence should be ascribed to Bi-related centers at distinct sites. We suggest Bi(2+) or Bi(+) centers adjacent to F vacancy defects are the origins of the observed NIR emissions.