2-μm emission performance of Tm~(3+)-Ho~(3+) co-doped tellurite glasses

The emission properties of 2-μm region fluorescence of Tm~(3+)-Ho~(3+) co-doped tellurite glasses are investigated. Introducing F~- ions to the composition of tellurite glasses plays a positive effect on the 2-μm emission.A maximum intensity of 2-μm emission is achieved when 1.5-mol%Tm_2O_3 and l-mol% Ho_2_O3 concentration are doped in the glasses.The emission cross section and gain coefficient of the ~5I_8→~5I_7 transition of Ho~(3+) are calculated.The emission cross section has a maximum of 1.29×10~(-2...     

Energy transfer mechanism in Er3＋ doped fluoride glass sensitized by Tm3＋ or no3＋ for 2.7-μm emission

Enhanced 2.7 μm emission is obtained in Er3＋/Tma＋ and Era＋/Ho3＋ codoped ZBYA glasses. Absorp- tion and emission spectra are tested to characterize the 2.7 μm emission properties of Era＋/Tm3＋ and Era＋/Ho3＋ doped ZBYA glasses and a reasonable energy transfer mechanism of 2.7 μm emission between Er3＋ and Tm3＋Ho3＋） ion is proposed. Codoping of Tm3＋ or Ho3＋ significantly reduces the lifetime of the Era＋： 4I13/2 level due to the energy transfer of Er3＋：4I13/2 →Tm3＋：3F4 or Er3＋：4I13/2 →Ho3＋： 5I7. Thus, the 2.7μm emission is strengthened and the 1,5μm emission is decreased accordingly especially in the Era＋/Tma＋ sample. The upconversion effects between the Er3＋/Tm3＋ and Er3＋/Ho3＋ doped ZBYA glasses are different attribute to the different energy transfer efficiencies. Both of the two codoped samples possess nearly equal large emission cross section （16.6 × 10 -21 cm-2） around 2.7 μm. The results indicate that this Er3＋/Tm3＋ or Er3＋/Ho3＋ doped ZBYA glass has potential applications in 2.7 μm laser.     

High Efficiency Infrared-to-Visible Upconversion Emission in Er^3＋,Yb^3＋, and Ho^3＋ Codoped Tellurite Glasses

A novel method of codoping the Er^3＋, Yb^3＋, and Ho^3＋ ions in tellurite glasses is demonstrated to obtain a high efficiency of infrared-to-visible upconversion. Three intense emission bands observed in Er^3＋, Yb^3＋, and Ho^3＋ codoped tellurite glasses centred at 525, 547, and 657nm correspond to Er^3＋： ^2H11/2 -4 ^4I15/2, Er^3＋： ^4S3/2 →^4I15/2＋Ho^3＋： ^5S2（^5F4） → ^5Is, and Er^3＋： ^4Sa/2 → ^4I15/2＋Ho^3＋： ^5F5 → ^5Is transitions, respectively. No visible upconversion quenching phenomenon is observed when three rare-earth ions are codoped together in tellurite glasses. In contrast, the upconversion intensity of red and green emissions in Er^3＋, Yb^3＋, and Ho^3＋ codoped glasses is enhanced largely when compared with Er^3＋ /Yb^3＋-codoped glasses. The dependence of upconversion intensities on excitation power and the possible upconversion mechanisms are evaluated. The three emissions are based on two-photon absorption processes.     

Spectroscopic properties in Er3＋/yb3＋ Co-doped fluorophosphate glass

Using the technique of high-temperature melting, a new Er3＋/Yb3＋ co-doped fluorophosphate glass was prepared. The absorption and fluorescence spectra were investigated in depth. The effect of Er3＋ and Yb3＋ concentration on the spectroscopic properties of the glass sample was also discussed. According to the Judd Ofelt theory, the oscillator strength was computed. The lifetime of 4113/2 level （t-m） of Er3＋ ions was 8.23 ms, and the full width at half maximum of the dominating emission peak was 68 nm at 1.53 μm. The large stimulated emission cross section of the Er3＋ was calculated by the McCumher theory. The spectroscopic properties of Er3＋ ion were compared with those in different glasses. The full width at half maximum and σe are larger than those of other glass hosts, indicating this studied glass may be a potentially useful candidate for high-gain erbium-doped fiber amplifier.     

Optimum fluorescence emission around 1.8 μm for LiYF4 single crystals of various Tm3＋-doping concentrations

In this paper, optical spectra of LiYF4 single crystals doped with Tm3＋ ions of various concentrations are reported. The emission intensity at 1.8 ktm first increases with increasing Tm3＋ concentration, and reaches a maximum value when the concentration of Tm3＋ is about 1.28 mol%, then it decreases rapidly as the concentration of Tm3＋ further increases to 3.49 mol%. The emission lifetime at 1.8 p.m also shows a similar tendency to the emission intensity. The maximum lifetime of 1.8 μm is measured to be 17.68 ms for the sample doped with Tm3＋ of 1.28 mol%. The emission cross section of 3F4 level is calculated. The maximum reaches 3.76 × 10 -21 cm2 at 1909 nm. The cross relaxation （3H6, 3H4 →3 F4, 3F4） between Tm3＋ ions and the concentration quenching effect are mainly attributed to the change of emission with Tm3＋ concentration. The largest quantum efficiency between Tm3＋ ions is estimated to be ,-147% from the measured lifetime and calculated radiative lifetime. All the results suggest that the Tm3＋/LiYF4 single crystal may have potential applications in 2 μm mid-infrared lasers.     

2.0-μm emission and energy transfer of Ho~(3+)/Yb~(3+) co-doped LiYF_4 single crystal excited by 980 nm

Ho3+/Yb3+co-doped Li YF4 single crystals with various Yb3+concentrations and ～ 0.98 mol% Ho3+concentration are grown by the Bridgman method under the conditions of taking Li F and YF3 as raw materials and a temperature gradient(40°C/cm–50°C/cm) for the solid–liquid interface.The luminescent performances of the crystals are investigated through emission spectra,infrared transmittance spectrum,emission cross section,and decay curves under excitation by 980 nm.Compared with the Ho3+single-doped Li YF4 crystal,the Ho3+/Yb3+co-doped Li YF4 single crystal has an obviously enhanced emission band from 1850 nm to 2150 nm observed when excited by a 980-nm diode laser.The energy transfer from Yb3+to Ho3+and the optimum fluorescence emission around 2.0 μm of Ho3+ions are investigated.The maximum emission cross section of the above sample at 2.0 μm is calculated to be 1.08×10-20cm2 for the Li YF4 single crystal of1-mol% Ho3+and 6-mol% Yb3+according to the measured absorption spectrum.The high energy transfer efficiency of88.9% from Yb3+to Ho3+ion in the sample co-doped by Ho3+(1 mol%) and Yb3+(8 mol%) demonstrates that the Yb3+ions can efficiently sensitize the Ho3+ions.     

Mechanisms and Concentration Dependence of Upconversion Fluorescence in Er^3＋ and Tm^3＋ Codoped Tellurite Glasses

We investigate the upconversion luminescence of Er3^ and Tm^3 codoped tellurite glasses under both the 975 and 80Ohm excitations. By Tm^3 codoping, the Er^3 green emission corresponding to the (^4S3/2, 2H11/2) → 4I15/2 transitions was quenched, while the red emission corresponding to the ^4F9/2 → ^4I15/2 transition was selectively sensitized. The red emission has a maximum in the range where the ratio of Er^3 - to Tm^3 -content is about two and its fluorescence intensity becomes 1.5 and 5 times larger at the maximum than those in the absence of Tm^3 for 975 and 800 nm excitations, respectively. The results were explained considering the influence of energy transfers between these two active ions.     

Optical parameters and energy levels splitting of Ho^3＋ in Ho^3＋： GdVO4

Ho^3＋ ： GdVO4 is a new laser material suitable for high-power laser systems. In this paper we measure the absorption spectra of Ho^3＋ in the sample Ho^3＋： GdVO4. The intensity parameters are calculated by using the Judd-Ofelt theory. Some predicted spectroscopic parameters, such as the spontaneous radiative transition rate, branching ratio and integrated emission cross section are dealt with. And we also compare the optical parameters with those of other materials. From these results, it is found that there are many transitions which have large oscillator strengths and large integrated emission cross sections. Especially the transitions such as ^5 F4 → ^5 I 8, ^5 S2→^5 I8, ^5 F5 → ^5 I8 and ^5 I7 →^ 5 I8 are useful in solid-state lasers and other fields. Finally, we discuss the splitting of the energy levels of Ho^3＋ in the crystal GdVO4 based on the group theory.     

Spectroscopic properties in Er³⁺/Yb³⁺ Co-doped fluorophosphate glass

Using the technique of high-temperature melting, a new Er 3+ /Yb 3+ co-doped fluorophosphate glass was prepared. The absorption and fluorescence spectra were investigated in depth. The effect of Er 3+ and Yb 3+ concentration on the spectroscopic properties of the glass sample was also discussed. According to the Judd–Ofelt theory, the oscillator strength was computed. The lifetime of 4 I 13/2 level (τ m ) of Er 3+ ions was 8.23 ms, and the full width at half maximum of the dominating emission peak was 68 nm at 1.53 μm. The large stimulated emission cross section of the Er 3+ was calculated by the McCumber theory. The spectroscopic properties of Er 3+ ion were compared with those in different glasses. The full width at half maximum and σ e are larger than those of other glass hosts, indicating this studied glass may be a potentially useful candidate for high-gain erbium-doped fiber amplifier.     

Broadband 1.5-um emission of erbium-doped TeO_2-WO_3-Nb_2O_5 glass for potential WDM amplifier

Erbium-doped glass showing the wider 1.5-um emission band is reported in a novel oxide system TeO2-WO3-Nb2O5 and their thermal stability and optical properties such as absorption, emission spectra, cross-sections and fluorescence lifetime were investigated. Compared with other glass hosts, the gain bandwidth properties of Er3+ in TWN glass is close to that of bismuth glasses, and larger than those of tellurite, germanate, silicate and phosphate glasses. The broad and flat 4I13/2-4I15/2 emission and the large stimulated emission cross-section of Er3+ ions around 1.5um can be used as host material for potential broadband optical amplifier in the wavelength-division-multiplexing (WDM) network system.     

Spectroscopic Properties of Yb^3＋-doped Germano-Silicate Glasses

We investigate the absorption, stimulated emission cross section and potential laser parameters of Yb^3 doped gernano-silicate glasses (GSY glass). The emission cross section is evaluated by using the measured absorption spectra and the principle of reciprocity. It is found that Yb^3 in GSY glasses has high stimulated emission cross section of 0.5-0.65pm^2 near 1020nm and exists long measured fluorescence lifetime of 1.20-2.00ms. Compared with other glass hosts, the GSY glass exhibits excellent general spectroscopic properties for Yb^3 -doped double-cladding fibres.     

Evaluation of Spectroscopic Properties of Yb^3＋ in Silicate—Based Heavy Metal Oxide Glasses

The absorption,stimulated emission cross section and potential laser parameters of heavy metal silicate glasses doped with Yb^3 ions have been investigated.The emission cross section has been evaluated by using the measured absoprtion spectra and principle of reciprocity.It is found that Yb^3 in SiO2-Bi2O3-B2O3 glass has high stimulated emission cross section of 0.09pm^2 for the 2F5/1→2F7/2 transition and exists short measured fluorescence lifetime of 0.78ms.On the other hand,the stimulated emission cross section of Yb^3 -doped SiO2-PbO glass was 0.49pm^2,Its measured fluorescence lifetime was 2.00ms.Evaluated from the good potential laser parameters,Yb^3 -doped SiO2-PbO glass may be a good candidate for fibre laser applications.     

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.     

Energy transfer relation of a novel Ce3＋/Pr3＋/Eu3＋ co-doped Sr2.975-xLaxAIO4＋xF1-x solid solution phosphor

The photoluminescence properties and energy transfer of a new Ce3＋/pr3＋/Eu3＋ co-doped solid-solution composi- tion of Sr2.975-xLaxAlO4＋xF1-x （LSAF） phosphor are investigated. Upon doping Pr3＋ into lattices of LSAF：Ce host, a shoulder emission peak is observed at about 620 nm, owing to the transition of 1D2 →3H4. Addition of Eu3＋ to LSAF：Ce3＋, Pr3＋ phosphor results in a sharp emission peaked at 675 nm for the 5D0 →TF3 transition and an increase of the intensity of red emission for Pr3＋ with increasing Eu3＋ concentration. The pathways of energy transfer among Ce3＋, Pr3＋, and Eu3＋ are proposed to be responsible for color addition of a red component to the primary yellow emission, enabling a potential adjustable color for blue excitable warm white.     

Blue upconversion luminescence in Tm3+/Yb3+ co-doped new oxyfluoride tellurite glass

The thermal stability, Raman spectrum and upconversion properties of Tm3+/Yb3+ co-doped new oxyfluoride tellurite glass are investigated. The results show that Tm3+/Yb3+ co-doped oxyfluoride tellurite glass possesses good thermal stability, lower phonon energy, and intense upconversion blue luminescence. Under 980-nm laser diode (LD) excitation, the intense blue (475 nm) emission and weak red (649 nm) emission corresponding to the 1G4 → 3H6 and 1G4 → 3F4 transitions of Tm3+ ions respectively,were simultaneously observed at room temperature. The possible upconversion mechanisms are evaluated.The intense blue upconversion luminescence of Tm3+/Yb3+ co-doped oxyfluoride tellurite glass can be used as potential host material for the development of blue upconversion optical devices.     

Up-conversion photoluminescence characteristics of Yb3+:Er3+:Tm3+ co-doped borosilicate glasses

Yb3+:Er3+:Tm3+ co-doped borosilicate glasses are prepared.Their strong up-conversion photoluminescence spectra in a range from ultra-violet to near-infrared,which are excited by a 978-nm laser diode,are measured,and the mechanisms of energy transfer among Yb3+,Er3+ and Tm3+ ions are discussed.The results show that there is an unexpected wavelength at 900-nm emission from Yb3+ Stark splitting levels to pump Tm3+ ions and there exists an optimum pump power.The concentration of the Tm3+ dopant gives rise to a prominent effect on the intensity of visible and near-infrared emissions for the Yb3+:Er3+:Tm3+ co-doped borosilicate glasses.     

Improved Fluorescence from Tm^3＋/Er^3＋/Ce^3＋ Triply Doped Bismuth-Silicate Glasses for S＋C-bands Amplifiers

Fluorescence of Tm^3＋/Er^3＋ codoped bismuth-silica （BS） glasses and the sensitization of Ce^3＋ are investigated, It shows that Ce^3＋ codoping with Tm^3＋/Er^3＋ in BS glasses results in a quenching of Tm^3＋ ion emission from ^3F4 to the ^3H6 level. Consequently, the 1.47μm emission occurs after the population inversion between the ^3H4 and ^3F4 levels. Furthermore, the codoped glasses show the broad emission spectra over the whole S and C bands with full-width at half-maximum （FWHM） up to about 119nm, as it combines 1.55μm emission band of Er^3＋ with 1.47μm emission band of Tm^3＋ under 800hm excitation.     

Investigation on Nonradiative Decay of the Er^3＋^4I13/2 → ^4I15/2 Transition in Different Tellurite Glass Matrix

Three kinds of Er^3＋-doped tellurite glasses with different hydroxyl groups are prepared by the conventional melt-quenching method. Infrared spectra are measured to estimate the exact content of OH^- groups in samples. The maximum phonon energy in glasses are obtained by measuring the Raman scattering spectra. The strength parameters Ωt （t = 2, 4, 6） for all the samples are calculated and compared. The nonradiative decay rate of the Er^3＋ ^4I13/2 → ^4I15/2 transition are calculated for the glass samples with different phonon energy and OH^- group contents. Finally, the effect of OH^- groups on fluorescence decay rate of Er^3＋ is analysed, the constant KOH-Er of TWN, TZPL and TZL glasses are calculated to be 9.2 × 10^-19 cm^4s^-1, 5.9 × 10^-19 cm^4s^-1, and 3.5 × 10^-19 cm^4s^-1, respectively.     

Lasing Characteristics of Tm^3＋：Ho^3＋ Codoped Silica Fibre Laser Pumped by 1.18-μm Raman Fibre Laser

The fundamental characteristics of Fabry-Perot-cavity continuous-wave Tm-Ho codoped silica fibre lasers pumped by a 1.18μm Raman fibre laser are presented. A maximum output power of 930mW at 1880nm is generated for a fibre length of 1 m from the transition of Tm^3 , with a slope efficiency of 32.4%. For a 3-m-long fibre, the maximum output power decreases to 650 mW at 1960 nm due to the laser emission from Ho^3 with a lower slope efficiency of 25%, which clearly shows the effective energy transfer from Tm^3 to Ho^3 . The wavelength redshifting of the laser emission originates from the transition competition and the emission cross section difference between Tm^3 and Ho^3 .     

Broadband amplified spontaneous emission from Er^3＋ -doped single-mode tellurite fibre

This paper reports on the fabrication and characterization of a newly erbium-doped single-mode tellurite glass-fibre applicable for 1.5-μum optical amplifiers. A very broad erbium amplified spontaneous emission in the range 1450--1650nm from erbium-doped single-mode tellurite glass-fibre is obtained upon excitation of a 980-nm laser diode. The effects of the length of glass-fibre and the pumping power of laser diode on the amplified spontaneous emission are discussed. The result indicates that the tellurite glass-fibre is a promising candidate for designing fibre-optic amplifiers and lasers.