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Ni 3 V 2 O 8 , regarded as an S  =  1 kagome staircase lattice antiferromagnet, possesses a novel magnetic field-temperature phase diagram. Specifically, a half plateau region is observed in the high field magnetization curve for magnetic fields in the range of 11-19 T. This experimental observation is theoretically unexpected for a standard kagome lattice antiferromagnet, and consequently, the underlying magnetic structure is still unclear. Multi-frequency electron spin resonance results in this study strongly support a collinear magnetic arrangement at the half plateau region. The resonant modes can be well fit by only considering the antiferromagnetic interactions on a four-spin sublattice of the spine sites.

The realization of upconversion at 808 nm excitation has shown great advantages in advancing the broad bioapplications of lanthanide-doped nanomaterials. In an 808 nm responsive system, Nd 3+ and Yb 3+ are both needed where Nd 3+ acts as a sensitizer through absorbing the excitation irradiation. However, few studies have been dedicated to the role of Yb 3+ . Here, we report a systemic investigation on the role of Yb 3+ by designing a set of core-shell-based nanostructures. We find that energy migration over the ytterbium sublattice plays a key role in facilitating the energy transportation, and moreover, we show that the interfacial energy transfer occurring at the core-shell interface also has a contribution to the upconversion. By optimizing the dopant concentration and surface anchoring the infrared indocyanine green dye, the 808 nm responsive upconversion is markedly enhanced. These results present an in-depth understanding of the fundamental interactions among lanthanides, and more importantly, they offer new possibilities to tune and control the upconversion of lanthanide-based luminescent materials.

Solid-state phosphor-converted white light-emitting diodes (pc-WLEDs) are currently revolutionizing the lighting industry. To advance the technology, phosphors with high efficiency, tunable photoluminescence, and high thermal stability are required. Here, we demonstrate that a simple lithium incorporation in NaAlSiO 4 :Eu system enables the simultaneous fulfillment of the three criteria. The Li substitution at Al sites beside Na sites in NaAlSiO 4 :Eu leads to an enhanced emission intensity/efficiency owing to an effective Eu 3+ to Eu 2+ reduction, an emission color tuning from yellow to green by tuning the occupation of different Eu sites, and an improvement of luminescence thermal stability as a result of the interplay with Li-related defects. A pc-WLED using the Li-codoped NaAlSiO 4 :Eu as a green component exhibits improved performance. The phosphors with multiple activator sites can facilitate the positive synergistic effect on luminescence properties.

Objective: To establish a method for measuring the photoelectric performance index (luminance response characteristic and luminance tolerance) of medical electronic endoscope., Methods: Based on the clinical application and product features of medical electronic endoscope, the umbrella grayscale test chart and the adjustable gray scale test chart are designed and made from two aspects of distribution and density differential., Results: The influence of gray scale arrangement, background illumination intensity and illumination spectrum on photoelectric performance measurement of electronic endoscope is verified by test., Conclusions: It is a reference for the design analysis, evaluation and modification of electronic endoscope product photoelectric part, whether it is suitable for fast detection of umbels and more accurate gray scale test chart.

Electrically driven red emission from MoS 2 -MoO 2 -MoO 3 (MS-MO) hybrid-based metal-semiconductor-metal (MSM) devices is reported for the first time. MoO 3 belts with high crystal quality and sufficient size are synthesized by thermal deposition. A layer of MS-MO hybrid is then produced on the belt surface to form MoO 3 /MS-MO core-shell by sulfurization. The devices exhibit unique electrical properties, a nonlinear I- V curve, and electric hysteresis characteristics at high applied biases (>2.4 V), where MS-MO hybrids act as electron transport channels. The electroluminescent current of the device increases to a set current limit over time when a constant bias is applied. The novel characteristics of the device are attributed to the space charge limited conduction (SCLC) mechanism occurring in MS-MO hybrids. The strong light emission is from recombination of excitons within the MoS 2 phase. This work develops a simple and effective method to drive MoS 2 to emit light on a large scale without using monolayer MoS 2 and vertical p-n junctions, indicating great potential for future 2D optoelectronics and photonics applications.

A mechanistic study of upconversion from lanthanides is of great importance for the fundamental research of upconversion materials and their diverse frontier applications. However, the most efficient upconversion of lanthanides is still obtained in a commonly used sensitizer-activator coupled system. Here we report a mechanistic investigation on the upconversion of Er3+ through self-sensitization which is applicable for 808, 980 and 1530 nm excitations. It is found that the cooperative energy transfer upconversion followed by cross-relaxation occurring among Er3+ ions plays a critical role in producing and enhancing the red upconversion for the samples with high dopant concentrations (e.g., >20 mol%). The red upconversion color can be further purified and enhanced by mediating the upconversion dynamics through introducing the lanthanides of Ho3+, Tm3+ and Yb3+, which can effectively contribute to the population in the red emitting state. Moreover, the energy migration in the Er-sublattice was also found to be a possible origin for quenching upconversion, which was proved and effectively suppressed by designing a tri-layered nanostructure where the distribution of Er3+ is spatially controllable. Our results gain access into the insight of upconversion dynamics in self-sensitization induced upconversion which would help the search for other new kinds of upconversion materials.

The discovery of high efficiency narrow-band green-emitting phosphors is a major challenge in backlighting light-emitting diodes (LEDs). Benefitting from highly condensed and rigid framework structure of UCr 4 C 4 -type compounds, a next-generation narrow green emitter, RbLi(Li 3 SiO 4 ) 2 :Eu 2+ (RLSO:Eu 2+ ), has emerged in the oxide-based family with superior luminescence properties. RLSO:Eu 2+ phosphor can be efficiently excited by GaN-based blue LEDs, and shows green emission at 530 nm with a narrow full width at half maximum of 42 nm, and very low thermal quenching (103%@150 °C of the integrated emission intensity at 20 °C), however its chemical stability needs to be improved later. The white LED backlight using optimized RLSO:8%Eu 2+ phosphor demonstrates a high luminous efficacy of 97.28 lm W -1 and a wide color gamut (107% National Television System Committee standard (NTSC) in Commission Internationale de L'Eclairage (CIE) 1931 color space), suggesting its great potential for industrial applications as liquid crystal display (LCD) backlighting., (© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Upconverting materials have achieved great progress in recent years, however, it remains challenging for the mechanistic research on new upconversion strategy of lanthanides. Here, a novel and efficient strategy to realize photon upconversion from more lanthanides and fine control of lanthanide donor-acceptor interactions through using the interfacial energy transfer (IET) is reported. Unlike conventional energy-transfer upconversion and recently reported energy-migration upconversion, the IET approach is capable of enabling upconversions from Er 3+ , Tm 3+ , Ho 3+ , Tb 3+ , Eu 3+ , Dy 3+ to Sm 3+ in NaYF 4 - and NaYbF 4 -based core-shell nanostructures simultaneously. Applying the IET in a Nd-Yb coupled sensitizing system can also enable the 808/980 nm dual-wavelength excited upconversion from a single particle. More importantly, the construction of IET concept allows for a fine control and manipulation of lanthanide donor-acceptor interactions and dynamics at the nanometer-length scale by establishing a physical model upon an interlayer-mediated nanostructure. These findings open a door for the fundamental understanding of the luminescence dynamics involving lanthanides at nanoscale, which would further help conceive new scientific concepts and control photon upconversion at a single lanthanide ion level.

Vertically stacked and laterally stitched heterostructures consisting of two-dimensional (2D) transition metal dichalcogenides (TMDCs) are predicted to possess novel electronic and optical properties, which offer opportunities for the development of next-generation electronic and optoelectronic devices. In the present work, we report the temperature-dependent synthesis of 2D TMDC heterostructures on Si/SiO 2 substrates, including MoS 2 -WS 2 , WS 2 -MoS 2 -WS 2 , Mo 1-x W x S 2 -WS 2 , and Mo 1-x W x S 2 alloyed bilayer heterostructures by ambient pressure chemical vapor deposition (CVD). Raman and photoluminescence mapping studies demonstrate that the as-produced heterostructures show distinct structural and optical modulation. Our results indicate that the evolution of various 2D heterostructures originates from the competition between the adsorption and desorption of Mo atoms and the diffusion of W atoms under various growth temperatures. This work sheds light on the design and fabrication of heterostructures using controllable interfaces and junctions of diverse TMDC atomic layers.

Current treatments for musculoskeletal disease and injury are restricted with the usage of autografts and allografts. Tissue engineering that applies the principles of biology and engineering to develop functional substitutes has potential promise of therapeutic regeneration for musculoskeletal tissues. However, engineering sizable tissues needs a vascular network to supply cells with nutrients, oxygen and signals after implantation. For this purpose, recent developments on therapeutic nanomaterials have been explored in delivering different vessel-inductive growth factors, small biomolecules and ions for scalable engineering into vascularizable scaffolds. Here, we provide an overview on the current efforts, and propose future perspectives for precise regulation on vascularization processes and musculoskeletal tissue functionality., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Following pioneering work, solution-processable Mn 4+ -activated fluoride pigments, such as A 2 BF 6 (A = Na, K, Rb, Cs; A 2 = Ba, Zn; B = Si, Ge, Ti, Zr, Sn), have attracted considerable attention as highly promising red phosphors for warm white light-emitting diodes (W-LEDs). To date, these fluoride pigments have been synthesized via traditional chemical routes with HF solution. However, in addition to the possible dangers of hypertoxic HF, the uncontrolled precipitation of fluorides and the extensive processing steps produce large morphological variations, resulting in a wide variation in the LED performance of the resulting devices, which hampers their prospects for practical applications. Here, we demonstrate a prototype W-LED with K 3 AlF 6 :Mn 4+ as the red light component via an efficient and water-processable cation-exchange green route. The prototype already shows an efficient luminous efficacy (LE) beyond 190 lm/W, along with an excellent color rendering index (Ra = 84) and a lower correlated color temperature (CCT = 3665 K). We find that the Mn 4+ ions at the distorted octahedral sites in K 3 AlF 6 :Mn 4+ can produce a high photoluminescence thermal and color stability, and higher quantum efficiency (QE) (internal QE (IQE) of 88% and external QE (EQE) of 50.6%.) that are in turn responsible for the realization of a high LE by the warm W-LEDs. Our findings indicate that the water-processed K 3 AlF 6 may be a highly suitable candidate for fabricating high-performance warm W-LEDs.

Near-infrared-to-near-infrared (NIR-to-NIR) anti-Stokes luminescence from Cr 3+ singly doped Ca 3 Ga 2 Ge 3 O 12 (CGGG) occurs under the excitation of an 808 nm diode laser. The anti-Stokes processes vary from one photon to two photon, depending on the Cr 3+ content (x) in Ca 3 Ga 2-x Cr x Ge 3 O 12 . The results suggest that phonon-assisted anti-Stokes excitation and cooperative energy transfer are involved in the observed upconversion (UC) processes of CGGG:Cr 3+ . The relevant Cr 3+ -doping-concentration-dependent NIR-to-NIR anti-Stokes luminescent mechanism, either one-photon or two-photon UC, is investigated. Such an observation on modulating the UC process via varying the doping concentration is helpful in broadening the understanding of UC phenomena.

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, 29 Si 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.

The resistance of a luminescent material to thermal quenching is essential for the application in high power LEDs. Usually, thermal luminescence quenching becomes more and more serious as the activator concentration increases. Conversely, we found here that a red phosphor Sr2P2O7:Bi(2+) is one of the exceptions to this as we studied the luminescence properties at low (10-300 K) and high (300-500 K) temperatures. As Bi(2+) ions are incorporated into Sr2P2O7, they exhibit the emissions at ∼660 and ∼698 nm at room temperature and are encoded, hereafter, as Bi(1) and Bi(2) due to the substitutions for two different crystallographic sites Sr(1) and Sr(2), respectively, in the compound. However, they will not substitute for these sites equally. At lower dopant concentration, they will occupy preferentially Sr(2) sites partially due to size match. As the concentration increases, more Bi(2+) ions start to occupy the Sr(1) sites. This can be verified by the distinct changes of emission intensity ratio of Bi(2) to Bi(1). As environment temperature increases, the thermal quenching happens, but it can be suppressed by the Bi(2+) concentration increase. This becomes even more pronounced in Bi(2+) heavily doped sample as we decompose the broad emission band into separated Bi(1) and Bi(2) Gaussian peaks. For the sample, the Bi(1) emission at ∼660 nm even shows antithermal-quenching particularly at higher temperatures. This phenomenon is accompanied by the blue shift of the overall emission band and almost no changes of lifetimes. A mechanism is proposed due to volume expansion of the unit cell, the increase of Bi(1) content, and temperature dependent energy transfer between Bi(2) and Bi(1). This work helps us better understand the complex luminescent behavior of Bi(2+) doped materials, and it will be helpful to design in the future the heavily doped phosphor for WLEDs with even better resistance to thermal quenching.

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.

Erbium-doped germanosilicate glasses with various cerium ions contents have been prepared. Optical absorption and 1.53 μm emission spectra were measured to characterize the spectroscopic performances of prepared samples. A detailed study of 1.53 μm spectroscopic properties was carried out when pumped by an 808 nm laser diode. Moreover, an energy level diagram and an energy transfer mechanism between Er3+ and Ce3+ were proposed to elucidate the enhanced 1.53 μm fluorescence. It is found that the prepared samples have optimal spectroscopic properties when the Ce3+ concentration is fixed to 0.5 mol. %. High spontaneous radiative transition probability (172.66  s(-1)), large effective emission bandwidth (74 nm), and emission cross section (9.49×10(-21)  cm(2) indicate that 808 nm pumped Er3+/Ce3+ codoped germanosilicate glass might be a suitable material for a broadband optical amplifier.

Phosphors with an efficient yellow-emitting color play a crucial role in phosphor-converted white LEDs (pc-WLEDs), but popular yellow phosphors such as YAG:Ce or Eu(2+) -doped (oxy)nitrides cannot smoothly meet this seemingly simple requirement due to their strong absorptions in the visible range. Herein, we report a novel yellow-emitting LuVO(4) :Bi(3+) phosphor that can solve this shortcoming. The emission from LuVO(4) :Bi(3+) shows a peak at 576 nm with a quantum efficiency (QE) of up to 68 %, good resistance to thermal quenching (T(50 %) =573 K), and no severe thermal degradation after heating-cooling cycles upon UV excitation. The yellow emission, as verified by X-ray photoelectron spectra (XPS), originates from the ((3)P(0),(3)P(1))→(1) S0 transitions of Bi(3+). Increasing the temperature from 10 to 300 K produces a temperature-dependent energy-transfer process between VO(4)(3-) groups and Bi(3+), and further heating of the samples to 573 K intensifies the emission. However, it subsequently weakens, accompanied by blueshifts of the emission peaks. This abnormal anti-thermal quenching can be ascribed to temperature-dependent energy transfer from VO(4)(3-) groups to Bi(3+), a population redistribution between the excited states of (3)P(0) and (3)P(1) upon thermal stimulation, and discharge of electrons trapped in defects with a trap depth of 359 K. Device fabrication with the as-prepared phosphor LuVO(4) :Bi(3+) has proved that it can act as a good yellow phosphor for pc-WLEDs., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Er(3+) doped Y2O3 and Nb2O5 modified germanate glasses with different Er(3+) concentrations were prepared. J-O intensity parameters were computed to estimate the structural changes due to the additions of Y2O3 and Nb2O5. The main mid-infrared spectroscopic features were investigated. To shed light on the observed mid-infrared radiative behavior, 975 nm and 1.53 μm emission spectra along with their decay lifetimes were also discussed. Moreover, the energy transfer processes of (4)I11/2 and (4)I13/2 level were quantitatively analyzed. In view of the experimental lifetimes, the simplified rate equation was utilized to calculate the energy transfer upconversion processes of upper and lower laser level of 2.7 μm emission. The theoretical calculations are in good agreement with the observed 2.7 μm fluorescence phenomena. Finally, the stimulated emission and gain cross sections were calculated and the results indicate that Er(3+) doped germanate glasses have great potential for mid-infrared application.

Large and ultrafast third-order optical nonlinearities in Ag-doped bismuthate glasses which are prepared by incorporating Ag ions into bismuthate glasses to form Ag nanoparticles through a consecutive melting-quenching-annealing technique are reported. Due to the high refractive index of bismuthate glass, surface plasmon resonance (SPR) of Ag nanoparticles is extendable to 1400 nm, resulting in a higher nonlinear refractive index than bismuthate glass. Femtosecond Z-scans show that the nonlinear refractive index, as high as 9.4 × 10(-17) and 5.6 × 10(-18) m(2) W(-1) at 800 and 1300 nm, respectively, can be achieved by selecting an optimized concentration of Ag nano-sized particles. And two-photon absorption at 800 nm is suppressed due to a blue shift in the band-gap of Ag-doped bismuthate glasses, as compared to pristine bismuthate glasses. Optical Kerr shutter technique reveals that these nonlinearities have a relaxation time of < 1 ps.

Transparent chalcogenide glass ceramics were prepared by thermally treating gold-doped germanium-gallium-sulfur glass. The gold, as nucleating agents, modified the crystallization process of the glass, resulting in the formation of nanocrystals belonging to a single α-Ga₂S₃ phase. The crystalline grains increased in number with the treatment duration while their size remained constant, leading to a high infrared transmittance of the glass ceramics. Z-scan measurements revealed the performance improvement of the α-Ga₂S₃ nanocrystals to third-order optical nonlinearities.

Structural design of photocatalysts is of great technological importance for practical applications. A rational design of architecture can not only promote the synthetic performance of photocatalysts but also bring convenience in their application procedure. Nanofibers have been established as one of the most ideal architectures of photocatalysts. However, simultaneous optimization of the photocatalytic efficiency, mechanical strength, and thermal/chemical tolerance of nanofibrous photocatalysts remains a big challenge. Here, we demonstrate a novel design of TiO2-SiO2 composite fiber as an efficient photocatalyst with excellent synthetic performance. Core-shell mesoporous SiO2 fiber with high flexibility was employed as the backbone for supporting ultrasmall TiO2 nanowhiskers of the anatase phase, constructing core@double-shell fiber with luffa-sponge-like appearance. Benefitting from their continuously long fibrous morphology, highly porous structure, and completely inorganic nature, the TiO2-SiO2 composite fibers simultaneously possess high photocatalytic reactivity, good flexibility, and excellent thermal and chemical stability. This novel architecture of TiO2-SiO2 glass composite fiber may find extensive use in the environment remediation applications.

Thermal luminescence quenching behavior of a phosphor is essential for application in phosphor converted white light emitting diodes (pc-WLEDs) because the phosphor layer can be heated up to 473K in a working high power WLEDs. Here, we have confirmed indeed a red luminescence of Mn(4+) substituting for calcium sites rather than tetrahedral aluminum sites in CaAl(4)O(7):Mn which can be synthesized in pure phase even with boron acid as flux, and examined the low and high temperature luminescent properties in the range of 10 to 500K. We have revealed as well as thermal quenching mechanism that distorted octahedral Mn(4+) sites suffer severe thermal quenching. This work, thus, hints a strategy to find a new Mn(4+) phosphor with better resistance to thermal impact in the future.

By combining upconversion nanoparticles (UCNPs) with rhodamine 6G (R6G) dye molecules, multicolor emission based on energy transfer is achieved. The complexes can be dissolved in epoxy resin, and self-assembled hemispherical microstructures are fabricated through a hydrophobic effect. A luminescence temperature sensor takes advantage of the high temperature sensitivity of the complexes due to energy transfer., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

We present a low noise single-frequency and single-polarization distributed Bragg reflector fiber laser at 1083 nm by using a 1.8 cm long newly developed ytterbium-doped phosphate single mode glass fiber. The maximum output power is more than 100 mW with a slope efficiency of >29.6%. The signal to noise ratio is higher than 61 dB and the laser linewidth of less than 2 kHz is estimated. The obtained relative intensity noise for frequencies of over 4.0 MHz is less than -150 dB/Hz, which approaches the shot noise limit. The achieved linear polarization extinction ratio is more than 30 dB.

Yttrium fluoride YF3:Er(3+) and yttrium oxyfluoride YOF:Er(3+) submicron-crystals with mid-infrared fluorescent emissions were synthesized for the first time. The rhombohedral phase YOF submicron-crystals were synthesized by the crystalline phase transformation from pure orthorhombic YF3 submicron-crystals, which were prepared by co-precipitation method. The composition and morphology were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM), which showed that submicron-crystals were quasi-spherical with the particle size of ~400 nm. A novel formation mechanism of YOF submicron-crystals was proposed. Photoluminescence (PL) spectra indicated the 2.7 μm emission of Er(3+) has remarkably enhanced with the increase of Er(3+) doping concentration, and a novel dynamic circulatory energy transfer mechanism was proposed. Fourier transform infrared spectra (FTIR) were used to demonstrate the change of hydroxyl content. These oxyfluoride submicron-crystals provide a new material for nano/submicron-crystals-glass composites, and open a brand new field for the realization of mid-infrared micro/nano-lasers.

Graphite like C3N4 (g-C3N4) was synthesized facilely via the low temperature thermal condensation of melamine between 300-650°C. The results showed that the products maintained as melamine when the temperature is below 300°C. With the increase of temperature, the products were transformed into carbon nitride and amorphous g-C3N4 successively. The morphology of products was changed from spherical nanoparticles of melamine into layer carbon nitride and g-C3N4 with the increase of temperature. The photoluminescence spectra showed that the carbon nitride products have continuous tunable photoluminescence properties in the visible region with increasing temperature. With the help of steady state, transient state time-resolved photoluminescence spectra and Raman microstructural characterization, a novel tunable photoluminescence mechanism was founded systematically, which is mainly related to the two dimensional π-conjugated polymeric network and the lone pair of the carbon nitride.

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.

The effects of temperature, pump power and excitation wavelength on near-infrared photoluminescence from Bi-doped multi-component germanate glasses are presented. Compared to conventional silica/silicate matrices, the examined material exhibits superior resistance to thermal quenching and less pronounced excited state absorption for pumping at 808 nm. It is shown that by selecting the optimal excitation wavelength, photoemission can be initiated from multiple active centers in parallel, resulting in an emission bandwidth (full width at half maximum) of more than 370 nm. Er3+/Bi co-doping is presented as an effective means to significantly enhance emission intensity around 1.5 μm by suppressing the typical Er3+-related red-to-green upconversion. Besides its relevance for Bi-doped materials, this also indicates a new route towards improving the performance of Er-based optical devices. The mechanism of Er3+→Bi energy transfer is examined in detail. Adjusting the molar ratio between both species provides an effective tool for tuning the emission scheme and further increasing emission bandwidth.

A compact, low-noise, single-frequency fiber laser by using a newly developed Yb³⁺ heavily doped single-mode phosphate glass fiber has been demonstrated. Over 400 mW stable continuous wave single transverse and longitudinal mode laser at 1.06 μm was achieved from a 0.8 cm long active fiber. The measured slope efficiency and estimated quantum efficiency of laser emission are 72.7% and 93%, respectively. The signal-to-noise ratio is higher than 72 dB, and the linewidth of the fiber laser is less than 7 kHz, while the measured relative intensity noise is less than -130 dB/Hz at frequencies of over 1.5 MHz.

This paper reports on intense blue upconversion in Tm(3+)/Yb(3+) codoped TeO(2)-Ga(2)O(3)-R(2)O(R=Li, Na, K) glasses upon excitation with commercial available laser diode (LD). Effects of alkali ions on the Raman spectra, thermal stability and spectroscopic properties of the tellurite-gallium glasses have also been investigated. Energy transfer and the involved upconversion mechanisms have been discussed. Intense blue upconversion emission centered at 476 nm along with a weak red emission at 650 nm has been observed upon excitation of 977 nm LD, assigned to the transitions of 1G4-->3H6, and 1G4-->3H4 and/or 3F(2,3)-->3H6 of Tm(3+), respectively. The blue upconversion intensity has a cubelike dependence on incident pump laser power, indicating a three-photon process. However, a quadratic dependence of the 476 nm upconversion intensity on the incident pump laser power has been observed when samples under excitation of 808 nm LD due to a two-photon absorption process. Enhanced upconversion luminescence have been observed with replacing K(+) for Na(+) and Li(+).