Mingying Peng

Near infrared broadband emission of bismuth-doped aluminophosphate glass

Near infrared broadband emission characteristics of bismuth-doped aluminophosphate glass have been investigated. Broad infrared emissions peaking at 1210nm, 1173nm and 1300nm were observed when the glass was pumped by 405nm laser diode (LD), 514nm Ar+ laser and 808nm LD, respectively. The full widths at half maximum (FWHMs) are 235nm, 207nm and 300nm for the emissions at 1210nm, 1173nm and 1300nm, respectively. Based on the energy matching conditions, it is suggested that the infrared emission may be ascribed to 3P1? 3P0 transition of Bi+. The broadband infrared luminescent characteristics of the glasses indicate that they are promising for broadband optical fiber amplifiers and tunable lasers.

Bismuth- and aluminum-codoped germanium oxide glasses for super-broadband optical amplification

Broadband infrared luminescence from bismuth-doped germanium oxide glasses prepared by a conventional melting-quenching technique was discovered. The absorption spectrum of the glasses covered a wide range from the visible to the near-infrared wavelength regions and consisted of five broad peaks below 370, 500, 700, 800, and 1000 nm. The fluorescence spectrum exhibited broadband characteristics (FWHM) greater than 300 nm with a maximum at 1300 nm pumped by an 808-nm laser. The fluorescence lifetime at room temperature decreased with increasing Bi2O3 concentration in the glass. Codoping of aluminum and bismuth was indispensable for the broadband infrared luminescence in GeO2:Bi, Al glass.

Infrared broadband emission of bismuth-doped barium-aluminum-borate glasses.

We report near infrared broadband emission of bismuth-doped barium-aluminum-borate glasses. The broadband emission covers 1.3microm window in optical telecommunication systems. And it possesses wide full width at half maximum (FWHM) of ~200nm and long lifetime as long as 350micros. The luminescent properties are quite sensitive to glass compositions and excitation wavelengths. Based on energy matching conditions, we suggest that the infrared emission may be ascribed to 3P1? 3P0 transition of Bi+. The broad infrared emission characteristics of this material indicate that it might be a promising candidate for broadband optical fiber amplifiers and tunable lasers.

Superbroadband 1310 nm emission from bismuth and tantalum codoped germanium oxide glasses

Near-infrared broadband emission from bismuth-tantalum-codoped germanium oxide glasses was observed at room temperature when the glasses were pumped by an 808 nm laser diode. The emission band covered the O, E, S, C, and L bands (1260-1625 nm), with a maximum peak at approximately 1310 nm, a FWHM broader than 400 nm, and a lifetime longer than 200 micros. The observed broadband luminescence was attributed to bismuth clusters in the glasses. Bismuth-tantalum-codoped germanium oxide glass might be promising as amplification media for broadly tunable lasers and wideband amplifiers in optical communications.

Tunable dual-mode photoluminescence from nanocrystalline Eu-doped Li2ZnSiO4 glass ceramic phosphors

We report on tunable photoluminescence from mixed-valence Eu-doped nanocrystalline Li2ZnSiO4 glass ceramics. After preparation of the precursor glass in air, gradual reduction of Eu3+ to Eu2+ occurs intrinsically during thermal annealing and precipitation of crystalline Li2ZnSiO4. Dual-mode photoemission can be generated for exciting at a wavelength of about 360 nm. The resulting colour of luminescence, ranging from orange/red to blue, can be controlled by adjusting the annealing temperature and, hence, the degree of crystallization: with increasing annealing temperature, the ratio of luminescence intensities related to Eu3+ and Eu2+ species, respectively, varies as a result of increasing degree of Eu3+-reduction as well as distinct changes in the optical scattering behaviour of the obtained glass ceramic. At the same time, the bandwidth of Eu2+-related photoemission increases from 87 to 154 nm. The underlying mechanisms of photoemission and energy transfer from Eu2+ to Eu3+ are discussed on the basis of dynamic emission spectroscopy and structural considerations, and a description of the internal reduction process is given.

Photoluminescence of Sr 2 P 2 O 7 :Bi 2+ as a red phosphor for additive light generation

We report on photoluminescence of Sr(2)P(2)O(7):Bi(2+) as a potential red-emitting phosphor for multichromatic light sources. If excited with blue light, photoluminescence of this compound spans the spectral range of about 600 to 760nm. Static and dynamic spectral data reveal the presence of two distinct emission centers. Based on bond covalency and emission lifetime, luminescence can clearly be assigned to Bi(2+) ions on Sr(1) and Sr(2) lattice sites, respectively. Energy transfer is observed from Bi(1) to Bi(2). Transfer efficiency, estimated from the lifetimes of the excited states, increases with increasing dopant concentration.

Broadband infrared luminescence from Li2O-Al2O3-ZnO-SiO2 glasses doped with Bi2O3.

The broadband emission in the 1.2~1.6mum region from Li2O-Al2O3-ZnO-SiO2 ( LAZS ) glass codoped with 0.01mol.%Cr2O3 and 1.0mol.%Bi2O3 when pumped by the 808nm laser at room temperature is not initiated from Cr4+ ions, but from bismuth, which is remarkably different from the results reported by Batchelor et al. The broad ~1300nm emission from Bi2O3-containing LAZS glasses possesses a FWHM ( Full Width at Half Maximum ) more than 250nm and a fluorescent lifetime longer than 500mus when excited by the 808nm laser. These glasses might have the potential applications in the broadly tunable lasers and the broadband fiber amplifiers.

Luminescence from Bi2+-activated alkali earth borophosphates for white LEDs.

Bi(2+)-doped MBPO(5) (M = Ba(2+), Sr(2+), Ca(2+)), synthesized in air via solid state reaction, are considered as novel orange and red phosphors for white light emitting diodes with improved colour quality. Absorption of Bi(2+) due to (2)P(1/2)-->(2)S(1/2) and (2)P(1/2)-->(2)P(3/2) could be observed and quantified. Excitation to (2)P(3/2) is accompanied by vibronic sidebands, and corresponding emission behaviour is found. The electron-phonon coupling strength increases in the order M = Ba(2+)-->Sr(2+)-->Ca(2+). In the case of MBPO(5):Bi(2+), one-, two- and even three-phonon sidebands could clearly be observed. The crystal structure of all three compounds belongs to space group P3(1)21. Bi(2+) is incorporated on M(2+) sites, and reduction of Bi(3+) to Bi(2+) occurs for reasons of charge compensation. In accordance with crystallographic data, fluorescence decay behaviour indicates that only one type of Bi(2+)-emission centers is present.

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.

Intense red photoluminescence from Mn 2+ -doped (Na + ; Zn 2+ ) sulfophosphate glasses and glass ceramics as LED converters

We report on intense red fluorescence from Mn(2+)-doped sulfophosphate glasses and glass ceramics of the type ZnO-Na(2)O-SO(3)-P(2)O(5). As a hypothesis, controlled internal crystallization of as-melted glasses is achieved on the basis of thermally-induced bimodal separation of an SO(3)-rich phase. Crystal formation is then confined to the relict structure of phase separation. The whole synthesis procedure is performed in air at <or= 800 degrees C. Electron spin resonance and Raman spectroscopy indicate that Mn(2+) species are incorporated on Zn(2+) sites with increasingly ionic character for increasing concentration. Correspondingly, in the glasses, increasing MnO content results in decreasing network polymerization. Stable glasses and continuously increasing emission intensity are observed for relatively high dopant concentration of up to 3 mol.%. Recrystallization of the glass results in strongly increasing emission intensity. Dynamic emission spectroscopy reveals only on type of emission centers in the glassy material, whereas three different centers are observed in the glass ceramic. These are attributed to octahedrally coordinated Mn(2+) in the residual glass phase and in crystalline phosphate and sulfate lattices, respectively. Relatively low crystal field strength results in almost ideal red emission, peaking around 625 nm. Excitation bands lie in the blue-to-green spectral range and exhibit strong overlap. The optimum excitation range matches the emission properties of GaN- and InGaN-based light emitting devices.