Er3+-doped phosphor-tellurite glass for broadband short-length Er3+-doped fiber amplifier

ErS+-doped phosphor-tellurite glass for broadband short-length Er3+-doped fiber amplifier (EDFA) is fabricated and characterized. The differential value (△T) of onset crystalline temperature (Tx) and glass transition temperature (Ts) is 206°C.     

Green and red up-conversion emissions and thermometric application of Er^3＋-doped silicate glass

The green and red up-conversion emissions centred at about 534, 549 and 663 nm of wavelength, corresponding respectively to the ^2H11/2 → ^4I15/2, ^4S3/2 → ^4I15/2 and ^4F9/2 → ^4I15/2 transitions of Er^3＋ ions, have been observed for the Er^3＋-doped silicate glass excited by a 978 nm semiconductor laser beam. Excitation power dependent behaviour of the up-conversion emission intensity indicates that a two-photon absorption up-conversion process is responsible for the green and red up-conversion emissions. The temperature dependence of the green up-conversion emissions is also studied in a temperature range of 296-673 K, which shows that Er^3＋-doped silicate glass can be used as a sensor in high-temperature measurement.     

Gain Characteristics of Er^3＋-Doped Phosphate Glass Fibres

An erbium-doped phosphate glass fibre has been drawn by the rod-in-tube technique in our laboratory. The gain for the Er^3＋-doped phosphate glass fibre with different pump powers and with different input signal wavelengths is investigated. The 2.2-cm-long fibre, pumped by a single-mode 980-nm fibre-pigtailed laser diode, can provide a net gain per unit length greater than 1.SdB/cm. The pump threshold is about 50mW at the wavelength of 1534nm, and below 70roW at 1550nm. The gain linewidth of the Er^3＋-doped phosphate glass fibre is greater than 34 nm and can cover the C band in optical communication networks.     

Transparent Ni^2＋-Doped MgO-Al2O3-SiO2 Glass Ceramics with Broadband Infrared Luminescence

We report on transparent Ni^2＋-doped MgO-Al2O3-SiO2 glass ceramics with broadband infrared luminescence. Ni^2＋-doped MgO-Al2O3-SiO2 glass is prepared by using the conventional method. After heat treatment at high temperature, MgAl2O4 crystallites are precipitated, and their average size is about 4.3 nm. No luminescence is detected in the as-prepared glass sample, while broadband infrared luminescence centred at around 1315 nm with full width at half maximum （FWHM） of about 300 nm is observed from the glass ceramics. The observed infrared emission could be attributed to the ^3T2g（^3F）→^3A2g（^3F） transition of octahedral Ni^2＋ ions in the MgAl2O4 crystallites of the transparent glass ceramics. The product of the fluorescence lifetime and the stimulated emission cross section is about 1.6×10^-24 s cm^2.     

Composition Dependence of Spectroscopic Properties of Er^3＋ Doped TeO2-WO3-ZnO Glasses

Er^3 -doped TeO2-WO3-ZnO glasses were prepared and the absorption spectra, emission spectra and fluorescence lifetimes were measured. With more Te02 content in the glasses, the emission full width at half maximum (FWHM) increases while the lifetime of the ^4I13/2 level of Er^3 decreases. The stimulated emission cross-sectionof Er^3 calculated by the McCumber theory is as large as 0.86pm^2. The product of the FWHM and the emissioncross-section σe of Er^3 in TeO2-WO3-ZnO glass is larger than those in other glasses, which indicates that the glasses are promising candidates for Er^3 -doped broadband amplifiers. The Judd-Otfelt parameter Ω6 shows close composition dependence of the 1.5μm emission bandwidth. The more the TeO2 content is, the larger thevalues of Ω6 and FWHM.     

Enhanced NIR emission in Ce^3＋/Er^3＋-doped YAG induced by Bi^3＋ doping

Ce^3＋/Er^3＋/Bi^3＋ triply-doped yttrium aluminum garnet （YAG） is synthesized using co-precipitation method. The Bi^3＋ concentration-dependent near-infrared （NIR） emission behavior is systemically in- vestigated. The NIR emission of Er^3＋ ions at 1531 nm is enhanced threefold by the addition of 7 mol% Bi^3＋. Bi^3＋doping results in the formation of exciton in YAG and the variation in the local environment of the doped rare-earth ions. The enhancement in NIR luminescence is ascribed to the combined effects of the sensitization of exciton→Ce^3＋ →Er^3＋ and the Bi^3＋ doping-induced adjustment of the local environment for Ce^3＋ and Er^3＋ ions.     

Frequency Upconversion Fluorescence Emission of Er^3＋-Doped Oxychloride Germanate Glass

Frequency upconversion fluorescence property of Er^3 -doped oxychloride germanate glass is investigated. Intense green and red emissions centred at 525, 546, and 657nm, corresponding to the transitions ^2H11/2→4I15/2,^4S3/2→^4I15/2, and ^4F9/2→^4I15/2, respectively, were simultaneously observed at room temperature. The quadratic dependence of the 525, 546, and 657nm emissions on excitation power indicates that a two-photon absorption process occurs under 975 nm laser diode (LD) excitation. The Raman spectrum investigation indicates that oxychloride germanate glass has the maximum phonon energy at-805cm^-1. The thermal stability of this oxychloride germanate glass is evaluated by differential scanning calorimetry, and thermal stability factor AT(△T = Tx -Tg) is 187℃. Intense upconversion luminescence and good thermal stability indicate that Er^3 -doped oxychloride germanate glass is a promising upconversion laser material.     

Structural and Luminescence Properties of Transparent Nanocrystalline ZrO2：Er^3＋ Films

The structural and luminescence properties of nanocrystalline ZrO2 ：Er^3＋ films are reported. Transparent nano-ZrO2 crystalline films doped with Er^3＋ have been prepared using a wet chemistry process. An intense roomtemperature emission at 1527nm with a full width at half-maximum of 46 nm has been observed, which is assigned to the ^4Ⅰ13/2 → ^4Ⅰ15/2 intra-4f^n electric transition of Er^3＋. Correlations between the luminescence properties and structures of the nanocrystalline ZrO2 ：Er^3＋ films have been investigated. Infrared-to-visible upconversion occurs simultaneously upon excitation of a commercially available 980-nm laser diode and the involved mechanisms have also been explained. The results indicate that the nanocrystalline ZrO2：Er^3＋ films might be suggested as promising materials for achieving broadband Er^3＋-doped waveguide amplifiers and upconversion waveguide lasers.     

Intense Green Upconversion Luminescence in Er^3＋：Yb^3＋ Codoped Fluorophosphate Glass Ceramic Containing SrTe5O11 Nanocrystals

Er^3＋ ：Yb^3＋ codoped tellurite-fluorophosphate （TFP） glass ceramic exhibits much stronger upconversion luminescence. The intensity of the 540nm green light and 651 nm red light of the TFP glass ceramic is 120 times and 44 times stronger than that of the fluorophospahte （FP） glass, respectively. XRD analysis shows that the nanocrystal in TFP glass ceramic is SrTe5O11. TFP glass ceramic also displays much higher upconversion fluorescence lifetime and crystallization stability. The narrow and strong peak at 540nm is very ideal for practical upconversion luminescence realization. This work is a new trial for exploring non-PbF2 involved nanocrystal upconversion glass ceramics.     

Upconversion properties of Er^3＋/Yb^3＋ co-doped TeO2-Nb2O5-Li2O glasses

The Er^3＋/Yb^3＋ co-doped TeO2-Nb2O5-Li2O glass is prepared by conventional melting method, and its upconversion spectra are measured. The intense green upconversion luminescence upon excitation with a 976 nm laser diode is observed with the naked eyes. The dependence of luminescence intensity on the ratio of Yb^3＋/Er^3＋ is discussed in detail, and the relationship between the ratio of green luminescence intensity to red luminescence intensity and the ratio of Yb^3＋/Er^3＋ is also studied, The luminescence intensity increases with the ratio of Yb^3＋/Er^3＋ increasing. The ratio of Yb^3＋/Er^3＋ plays a more important role than the concentration of Er^3＋ in determining the upconversion luminescence intensity. The ratio of green luminescence intensity to red luminescence intensity reaches a maximum when ratio of Yb^3＋/Er^3＋ is 3. Thus the glass could be one of the potential candidates for LD pumping solid-state lasers.     

Broadband and High Efficient 1530 nm Emission from Oxyfluoride Glass Ceramics Codoped with Er3＋ and Yb3＋ Ions

The emission at 1530nm and its applications in optical communications are discussed. The efficient width of the emission band △eff, which is up to 91 nm, is larger as compared with silica-based glass, bismuth glass and ZrF4-BaF2-LaFa-AIF3-NaF （ZBLAN） glass doped by Er^3＋ ions. Under the excitation of 785 nm laser, the emission integral intensity of 153Onto increases about five times in the glass ceramics higher than that in the glass. This is explained by the quantum cutting process by two-photon emission with phonon assistance. The results indicate that the glass ceramics are a promising candidate for developing broadband optical amplifiers in wavelength-division multiplexed systems.     

Effect of lithium-potassium mixed alkali on spectroscopic properties of Er^3＋-doped aluminophosphate glasses

Er^3＋-doped lithium-potassium mixed alkali aluminophosphate glasses belonging to the oxide system xK2O-（15-x）Li2O-4B2O3-11Al2O3-5BaO-65P2O5 are obtained in a semi-continuous melting quenching process. Spectroscopic properties of Er^3＋-doped glass matrix have been analysed by fitting the experimental data with the standard Judd-Ofelt theory. It is observed that Judd-Ofelt intensity parameters Ωt（t = 2, 4 and 6） of Er^3＋ change when the second alkali is introduced into glass matrix. The variation of line strength Sed[^4I13/2,^4I15/2] follows the same trend as that of the/26 parameter. The effect of mixed alkali on the spectroscopic properties of the aluminophosphate glasses, such as absorption cross-section, stimulated emission cross-section, spontaneous emission probability, branching ratio and the radiative lifetime, has also been investigated in this paper.     

Short Tm^3＋-doped fiber lasers with watt-level output near 2 μm

High-power operation of diode-pumped fiber lasers at wavelength near 2 μm are demonstrated with short length of heavily Tm^3＋-doped silica glass fibers. With 7-cm long fiber, a laser at near 2 μm is obtained with the threshold of 135 mW, maximum output power of 1.09 W, and slope efficiency of 9.6% with respect to the launched power from a laser diode at 790 nm. The output stability of this fiber laser is within 5%. The dependence of the performance of fiber lasers on the operation temperature and cavity configuration parameters is also investigated.     

Broadband Near-Infrared Emission from Transparent Ni^2＋ -Doped Sodium Aluminosilicate Glass Ceramics

Broadband near-infrared emission from transparent Ni^2＋-doped sodium aluminosilicate glass-ceramics is observed. The broad emission is centred at 1290nm and covers the whole telecommunication wavelength region （1100- 1700hm） with full width at half maximum of about 340hm. The observed infrared emission could be attributed to the 3T2（F） → 3A2（F） transition of octahedral Ni^2＋ ions that occupy high-field sites in nanocrystals. The product of the lifetime and the stimulated emission cross section is 2.15 × 10^-24 cm^2s. It is suggested that Ni^2＋- doped sodium aluminosilicate glass ceramics have potential applications in tunable broadband light sources and broadband amplifiers.     

Er^3＋/Tm^3＋/Yb^3＋ tridoped oxyfluoride glass ceramics with efficient upconversion white-light emission

A novel Tm^3＋/Yb^3＋ triply-doped glass ceramics containing BaF2 nano-crystals are successfully prepared. Fluoride nanocrystals BaF2 are successfully precipitated in glass matrix, which is affirmed by the X-ray diffraction results. The intense blue （476 nm）, green （543 nm）, and red （656 nm） emissions of the glass ceramics are simultaneously observed at room temperature under 980-am excitation, and the emission luminescence intensity increases significantly compared with the precursor glass, which is attributed to the low phonon energy of fluoride nanocrystals when rare-earth ions are incorporated into the precipitated BaF2 nanocrystals. Under 980-nm excitation at 400 mW, the international commission on illumination （CIE） chromaticity coordinate （X = 0.278, Y = 0.358） of the tridoped oxyfluoride glass ceramics＇ upconversion emissions is close to the standard white-light illumination （X = 0.333, Y= 0.333）. The results indicate that Tm^3＋/Yb^3＋ triply doped glass ceramics can act as suitable materials for potential three-dimensional displays applications.     

Broadband Infrared Luminescence of Ni^2＋ in Petalite-Type Transparent Glass Ceramics

Transparent Ni^2＋-doped magnesium aluminosilicate glass ceramics are prepared. The formation of petalite-type crystallites in the glass ceramics is confirmed by x-ray diffraction. Broadband infrared luminescence centred at around 1235nm with full width at half maximum （FWHM） of about 300nm is observed from the Ni^2＋-doped glass ceramics. The observed infrared emission could be attributed to the ^3T2（F） → ^3A2（F） transition of octahedral Ni^2＋ ions in petalite-type crystallites. Theproduct of the fluorescence lifetime and the stimulated emission cross sections is 1.2 ×10-24 cm^2s.     

Spectroscopic properties and mechanism of Tm^3＋/Er^3＋/Yb^3＋ co-doped oxyfluorogermanate glass ceramics containing BaF2 nanocrystals

Transparent Tm^3＋/Er^3＋/yb^3＋ co-doped oxyfluorogermanate glass ceramics containing BaF2 nanocrystals are prepared. Under excitation of a 980-nm laser diode （LD）, compared with the glass before heat treatment, the Tm^3＋/Er^3＋/yb^3＋ co-doped oxyfluorogermanate glass ceramics can emit intense blue, green and red up-conversion luminescence and Stark- split peaks; X-ray diffraction （XRD） and transmission electron microscope （TEM） results show that BaF2 nanocrystals with an average diameter of 20 nm are precipitated from the glass matrix. Stark splitting of the up-conversion luminescence peaks in the glass ceramics indicates that Tm^3＋, Er^3＋ and （or） Yb^3＋ ions are incorporated into the BaF2 nanocrystals. The up-conversion luminescence intensities of Tm^3＋, Er^3＋ and the splitting degree of luminescence peaks in the glass ceramics increase significantly with the increase of heat treat temperature and heat treat time extension. In addition, the possible energy transfer process between rare earth ions and the up-conversion luminescence mechanism are also proposed.     

Host dependent thermal stability and frequency upconversion of Er^3＋-doped heavy metal oxyfluoride germanate glasses

The upconversion properties of Er^3＋-doped heavy metal oxyfluoride germanate glasses under 975 nm excitation have been investigated. The intense green （551 and 529 nm） and relatively weak red （657 nm） emissions corresponding to the transitions ^4S3/2→^4I15/2, ^2H11/2→^4 I15/2 and ^4F9/2 →^4I15/2, respectively, were simultaneously observed at room temperature. The content of PbF2 has an important influence on the upconversion luminescence emission. With increasing content of PbF2, the intensities of green （529 nm） and red （657 nm） emissions increase slightly, while the green emission （551 nm） increases markedly. These results suggest that PbF2 has an influence on the green （551 nm） emission more than on the green （529 nm） and red （657 nm） emissions.     

The LD-Cladding-Pumped High Power Tm^3＋ -doped Silica Fibre Amplifying at Approximately 1.99 μm

A laser diode （LD） cladding-pumped cw Tm^3＋ -doped silica fibre amplifier is reported that provides up to 3 W output with the slope efficiency nearly 30%. The gain fibre is 27.5/400μm D-shaped Tm^3＋ -doped silica double- cladding fibre, and the input signal sources is an LD-pumped Tm^3＋：YAP lasing at 1.99μm. The measured amplified spectrum only stretches a little relative to the input signal spectrum. This is the first report to the authors＇ knowledge of general experimental investigation of cladding-pumped Tm^3＋ -doped fibre amplifier of high power cw at 1.99μm.     

Comparative study of spectroscopic properties of Er^3＋／Yb^3＋-codoped tellurite glass and fibres under 980nm excitation＊

A tellurite fibre of TeO_{2}－ZnO－La_{2}O_{3}－Li_{2}O glass codoped with 20000 ppm ytterbium and 5000 ppm erbium was fabricated by the suction casting and rod-in-tube technologies. The absorption spectrum of Er^{3+}/Yb^{3+} -codoped bulk glass has been measured. From the Judd－Ofelt intensity parameters, the spontaneous emission probability and radiative lifetime τ_{rad} of Er^{3+}:{}^{4}I_{13/2}→{}^{4}I_{15/2} transition for the bulk glass have been calculated. The emission fluorescence spectra and lifetimes around 1.5μm, and subsequent upconversion fluorescence in the range of 500－700nm were measured in fibres and compared with those in bulk glass. The changes in amplified spontaneous emission with fibre length and pumping power was also measured. It was found that the emission spectrum from erbium in fibres is almost twice as broad as the corresponding spectrum in bulk glass when pumped at 980nm.