Superbroad near-to-mid-infrared luminescence from Bi5(3+) in Bi5(AlCl4)3

Bismuth Infrared Star: Being at a Glance

Bismuth polycations have garnered significant attention from researchers due to their extraordinary and counter-intuitive structures and stoichiometries. Despite extensive experimental and theoretical investigations, understanding of the bonding in such clusters remains insufficient. An AdNDP bonding analysis was conducted to elucidate the bonding characteristics using both homoatomic and heteroatomic bismuth clusters with various stoichiometries. Analysis of the calculated nucleus-independent chemical shift data confirmed the aromatic nature of these species. Universal bonding patterns were identified that can be applied to a range of homoatomic and heteroatomic bismuth clusters. Additionally, calculations of absorbance and fluorescence spectra were performed to gain insights into the near-infrared emission and establish a potential correlation between absorbance and the identified bonding patterns.

Ultra-broadband red to NIR photoemission from multiple bismuth centers in Sr2B5O9Cl:Bi crystal

Bismuth (Bi)-doped materials are a new family of laser materials, and they usually exhibit extremely broad near-infrared (NIR) luminescence in 1000-1700 nm. Therefore, they can be utilized for a new generation of ultra-broadband tunable laser sources and ultra-broadband fiber amplifier. The broadband characteristics of Bi-active NIR luminescence can meet the needs of special wavelength laser sources that rare-earth-doped lasers cannot provide. However, at present, the Bi-doped NIR luminescence materials are mainly concentrated on glass, while Bi-doped NIR luminescence laser crystals are rarely reported. In this work, a novel Bi-doped crystal Sr₂B₅O₉Cl:Bi is reported with NIR luminescence, which exhibits broadband absorption in ultraviolet and visible regions, and can produce ultra-broadband from red to NIR luminescence covering 600-1600 nm. The results of excitation, emission spectra, and fluorescence lifetime show that the Sr₂B₅O₉Cl:Bi crystal contains three different Bi-active NIR emission centers. This work could enrich our understanding on Bi NIR emission behaviors in crystals. And this material provides a possibility for the development of a new laser source.

Two-Dimensional-Layered Perovskite ALaTa2O7:Bi3+ (A = K and Na) Phosphors with Versatile Structures and Tunable Photoluminescence

Topological chemical reaction methods are indispensable for fabricating new materials or optimizing their functional properties, which is particularly important for two-dimensional (2D)-layered compounds with versatile structures. Herein, we demonstrate a low-temperature (∼350 °C) ion exchange approach to prefabricate metastable phosphors ALa_{1- x}Ta₂O₇: xBi³⁺ (A = K and Na) with RbLa_{1- x}Ta₂O₇: xBi³⁺ serving as precursors. The as-prepared ALa_0.98Ta₂O₇:0.02 Bi³⁺ (A = Rb, K, and Na) share the same Dion-Jacobson type 2D-layered perovskite phase, and photoluminescence analyses show that ALa_0.98Ta₂O₇:0.02 Bi³⁺ (A = Rb, K, and Na) phosphors exhibit broad emission bands peaking at 540, 550, and 510 nm, respectively, which are attributed to the nonradiative transition of Bi³⁺ from excited state ³P₁ or ³P₀ to ground state ¹S₀. The various Bi³⁺ local environments at the crystallographic sites enable the different distributions of emission and excitation spectra, and the photoluminescence tuning of ALa_0.98Ta₂O₇:0.02 Bi³⁺ (A = Rb, K, and Na) phosphors are realized through alkali metal ion exchange. Notably, the combination of superior trivalent bismuth emission and low-temperature ion exchange synthesis leads to a novel yellow-emitting K(La_0.98Bi_0.02)Ta₂O₇ phosphor which is successfully applied in a white LED device based on a commercially available 365 nm LED chip. Our realizable cases of this low-temperature ion exchange strategy could promote exploration into metastable phosphors with intriguing properties.

Unusual anti-thermal degradation of bismuth NIR luminescence in bismuth doped lithium tantalum silicate laser glasses

For application of bismuth laser glasses in either fiber amplifier or laser, their performance stability in long run should be understood especially in extreme conditions. However, so far, there are few reports on it. Here, we found, after the cycle experiments on heating and cooling, that the proper increase of lithium content in lithium tantalum silicate laser glass can lead to unusual anti-thermal degradation of bismuth NIR luminescence, which completely differs from the scenario in germanate glass. FTIR, ²⁹Si MAS NMR spectra, absorption and dynamic photoluminescence spectra are employed to unravel how this happens. The results illustrate that it should be due to the decrease of polymerization of silicate glass network, which in turn allows the regeneration at 250°C, and therefore, the content increase of bismuth NIR emission centers. In the meanwhile, we noticed though Bi luminescence can be thermally quenched its peak does not shift along with temperature, which seldom appears in laser materials. The unique property might guarantee the unshift of Bi fiber laser wavelength once such glass was made into fiber devices even as the environmental temperature changes. The role of lithium is discussed in the evolution of glass structures, the suppression of glass heterogeneity, and the thermal stability of Bi luminescence, and it should be helpful to design homogeneous silicate laser glass with outstanding thermal stability.

Superbroad visible to NIR photoluminescence from Bi+ evidenced in Ba2B5O9Cl: Bi crystal

The nature of bismuth NIR luminescence is essential to develop the bismuth doped laser materials with high efficiency and desirable emission wavelength, and it, thereby, receives rising interests. Our previous work reported the Bi(0) luminescence from Ba2B5O9Cl: Bi with a lifetime of ~30 μs and the conversion of Bi(2+) to Bi(0). This work found indeed the conversion could be enabled in the compound by an in situ reduction technique and it, however, happens via an intermediate state of Bi(+). Once the ion of Bi(+) is stabilized and built into the compound, it can luminesce in a super broad spectral range from 600 to 1200 nm with a lifetime longer than 1 ms, due to the cascade transitions from (3)P2 and (3)P1 to (3)P0. This is completely different from Bi(0) and Bi(2+) in the compound, and it has never been noticed before. We believe this work can help us better understand the complex nature of bismuth luminescence.

Energy transfer and luminescence properties of Sr[1-3(x+y)/2]Al₂B₂O₇:xEu³⁺, yBi³⁺ phosphor

Sr[1-3(x+y)/2]Al2B2O7:xEu(3+), yBi(3+) (x=0-5 mol% and y=0-5 mol%) phosphors are synthesized by a solid-state reaction method in air, and their crystal structure, fluorescence lifetime, and luminescence properties are investigated. The optimal composition is determined to be (Sr0.94Eu0.03Bi0.01)Al2B2O7. The PLE band peaks within the range 200-550 nm are due to O(2-)→Eu(3+) charge transfer band, (7)F0→(5)H3, (5)D4, (5)L7, (5)L6, (5)D3, (5)D2, and (5)D1 transitions, respectively. The strongest PL band peak under excitation 394 nm light is at ∼615 nm owing to (5)D0→(7)F2 transition of Eu(3+) ion. The PL intensity of Eu(3+), Bi(3+) co-doped SrAl2B2O7 phosphor is 1.3 times that of Eu(3+) doped SrAl2B2O7 phosphor due to the energy transfer between Eu(3+) and Bi(3+) ions, which is explained by the energy level diagrams of Bi(3+) and Eu(3+) ions. The CIE chromaticity coordinates of Sr0.955Al2B2O7:0.03Eu(3+) and Sr0.94Al2B2O7:0.03Eu(3+), 0.01Bi(3+) phosphors under excitation 394 nm light are (x=0.6292, y=0.3702) and (x=0.6284, y=0.3711), respectively. These phosphors will be used as reddish orange emitting phosphor candidate for white LED with ∼394 nm near ultraviolet LED chip.

Homogeneity of bismuth-distribution in bismuth-doped alkali germanate laser glasses towards superbroad fiber amplifiers

Compared to rare-earth doped glasses, bismuth-doped glasses hold promise for super-broadband near-infrared (NIR) photoemission and potential applications in optical amplification. However, optically active bismuth centers are extremely sensitive to the properties of the surrounding matrix, and also to processing conditions. This is strongly complicating the exploitation of this class of materials, because functional devices require a very delicate adjustment of the redox state of the bismuth species, and its distribution throughout the bulk of the material. It also largely limits some of the conventional processing routes for glass fiber, which start from gas phase deposition and may require very high processing temperature. Here, we investigate the influence of melting time and alkali addition on bismuth-related NIR photoluminescence from melt-derived germanate glasses. We show that the effect of melting time on bismuth-related absorption and NIR photoemission is primarily through bismuth volatilization. Adding alkali oxides as fluxing agents, the melt viscosity can be lowered to reduce either the glass melting temperature, or the melting time, or both. At the same time, however, alkali addition also leads to increasing mean-field basicity, what may reduce the intensity of bismuth-related NIR emission. Preferentially using Li2O over Na2O or K2O presents the best trade-off between those above factors, because its local effect may be adverse to the generally assumed trend of the negative influence of more basic matrix composition. This observation provides an important guideline for the design of melt-derived Bi-doped glasses with efficient NIR photoemission and high optical homogeneity.

Efficient 2.05 μm emission of Ho3+/Yb3+/Er3+ triply doped fluorotellurite glasses

The 2.05 μm emission has been obtained using a 980 nm laser excitation in Ho(3+)/Yb(3+)/Er(3+) triply doped fluorotellurite glass. Strong emission near 2.05 μm is demonstrated and the corresponding energy transfer mechanisms are discussed and analyzed according to the photoluminescence performance and absorption measurements. Yb(3+) and Er(3+) ions can absorb the pumping energy and transfer it to Ho(3+) ions efficiently. These results indicate that this Ho(3+)/Yb(3+)/Er(3+) triply doped fluorotellurite glass has potential applications in 2.0 μm laser.

Ho³⁺Yb³⁺-codoped germanate-tellurite glasses for 2.0 μm emission performance

2.0 μm emission property of a new germanate-tellurite (GT) glass with Ho³⁺/Yb³⁺ codoping is synthesized and analyzed. Efficient 2.0 μm emission of Ho³⁺ ions sensitized by Yb³⁺ ions from the host glass was observed under 980 nm pumping. Based on the measured absorption spectra, the Judd-Ofelt parameters were calculated and discussed. The maximum emission cross section of Ho³⁺ ions transition is 4.36×10(-21) cm2 around 2.0 μm. The energy transfer efficiency is calculated and fitted the decay signals. The good spectroscopic properties suggest that Ho³⁺/Yb³⁺-codoped GT glass may become an attractive host for developing solid state lasers operating in the mid-infrared.

Ultra-broadband infrared luminescence of Bi-doped thin-films for integrated optics

Ultra-broadband infrared luminescence has been observed in bismuth (Bi)-doped germanate thin-films prepared by pulsed laser deposition. The films are compatible with various types of substrates, including conventional dielectrics (LaAlO(3), silica) and semiconductors (Si, GaAs). The emission peak position of the films can be finely tuned by changing oxygen partial pressure during the deposition, while the excitation wavelength locates from ultra-violet to near-infrared regions. The physical mechanism behind the observed infrared luminescence of the Bi-doped films, differing from that of the as-made glass, is discussed.

Yellow-to-orange emission from B2+-doped RF2 (R = Ca and Sr) phosphors

RF2:Bi (R = Ca and Sr) phosphors were synthesized by solid state reaction method in air and their luminescence properties were investigated. Broad yellow-to-orange emissions peaking at ~550 nm (CaF2:Bi) and ~600 nm (SrF2:Bi) were observed under ~260 nm excitation. The emission centers inRF2:Bi (R = Ca and Sr) phosphors are Bi2+ ions, and the excitation and emission bands of RF2:Bi (R = Ca and Sr) phosphors can be attributed to 2P 1/2 → 2S 1/2 and 2P 3/2(1) → 2P 1/2 transitions of Bi2+ ions, respectively. The phosphors are promising for application in lighting due to broad yellow-to-orange emission.

Broadband infrared luminescence in γ-ray irradiated bismuth borosilicate glasses

The influence of γ-ray irradiation on the optical properties of Bi(2)O(3)-B(2)O(3)-SiO(2) glass has been investigated. Broadband infrared (IR) emission at 1310 nm with a FWHM over 200 nm is observed in the γ-ray irradiated glass. The IR luminescence depends on the γ-ray irradiation dose and the concentration of Bi(2)O(3). The thermal stability of the γ-ray irradiated IR luminescence center is studied, and the origin of the IR luminescence center has been suggested.

Near-infrared to mid-infrared photoluminescence of Bi2O3-GeO2 binary glasses

Near-infrared and mid-infrared (MIR) ultrabroad emission bands were observed in as-grown and annealed Bi(2)O(3)-GeO(2) binary glasses, in the wavelength ranges of 1000-1800 nm and 1800-3020 nm, respectively. The MIR emission band could appear through high doping ratio of Bi(2)O(3) or annealing process in air atmosphere. The structure of these glasses, the transformation of emission centers, and the effect of Al ions doping have been discussed, with the conclusion that the Bi(2)O(3)-GeO(2) binary glasses could be a promising laser material.

Broadband NIR luminescence from a new bismuth doped Ba2B5O9Cl crystal: evidence for the Bi0 model

A new type of bismuth doped Ba(2)B(5)O(9)Cl crystal is reported to exhibit broadband near infrared (NIR) photoluminescence at room temperature, which has been identified here originating from elementary bismuth atom. Rietveld refining, static and dynamic spectroscopic properties reveal two types of Bi(0) centers in the doped compound due to the successful substitution for two different nine-coordinated barium lattice sites. These centers can be created only in a reducing condition, and when treated in air and N(2)/H(2) flow in turn, they can be removed and restored reversely. As the dwelling time is prolonged in N(2)/H(2) at high temperature, conversion from Bi(2+) to Bi(0), as reflected by changes of their relative emission intensities, is witnessed in the crystal of Ba(2)B(5)O(9)Cl:Bi. The lifetime of the NIR luminescence was observed in a magnitude of ~30 μs, rather different from bismuth doped either glasses or crystals reported previously.

Superbroad near to mid infrared luminescence from closo-deltahedral Bi5(3+) cluster in Bi5(GaCl4)3

Closo-deltahedral Bi(5)(3+) cluster in Bi(5)(GaCl(4))(3), which can be synthesized in benzene by oxidizing bismuth metal either with BiCl(3) or GaCl(3), respectively, can absorb ultraviolet, visible and infrared lights, and luminesce superbroadly in near to mid infrared (NMIR) spectral range from 1 to 3μm at room temperature. Slight geometry change of the cluster can lead to the redshift of emission peak. These observations may initialize the development of Bi-based NMIR light sources with superbroad emission spectrum, where Bi(5)(3+) or similar polycationic species act as activators. Disputable crystal structure of Bi(5)(GaCl(4))(3) was redefined by classic Rietveld refining analysis. Consistent with crystallographic data, excitation, emission, temporal decay and time-resolved infrared emission spectra all reveal only one type of luminescent centers, viz. Bi(5)(3+), in the compound. And a new absorption of Bi(5)(3+) was found at ~1100nm.

A new study on bismuth doped oxide glasses

Spectroscopic properties of bismuth doped borate, silicate and phosphate glasses have been reinvestigated in this work. It shows the typical decay time of Bi(3+) is around 500ns rather than 2.7-to-3.9 μs reported by Parke and Webb at room temperature. Introduction of higher content either alkali or alkali earth into borate glasses favors the Bi(3+) emission. As the contents increase excitation peak shifts regularly red while emission peak shows reverse trend. This, as revealed by Huang-Rhys factor, is due to the weakening of coupling between bismuth and glass host, and it can be interpreted within the frame of configurational coordinate diagrams. Differently, as bismuth concentration increases, both the excitation and emission shift red. The unknown origin of red emission from bismuth doped calcium or magnesium phosphate glass has been identified as Bi(2+) species on the basis of excitation spectrum and emission lifetime particularly after comparing with Bi(2+) doped materials. No near infrared (NIR) emission can be detected in these glasses within instrument limit.

On the origin of near-IR luminescence in Bi-doped materials (II). Subvalent monocation Bi⁺ and cluster Bi₅³⁺ luminescence in AlCl₃/ZnCl₂/BiCl₃ chloride glass

Broadband NIR photoluminescence (from 1000 to 2500 nm) was observed from partially reduced AlCl₃/ZnCl₂/BiCl₃ glass, containing subvalent bismuth species. The luminescence consists of three bands, assigned to Bi⁺ , Bi₂⁴⁺, and Bi₅³⁺ ions. The physical and optical characteristics of these centers and possible contribution to NIR luminescence from bismuth-doped oxide glasses are discussed.