Photoluminescence and energy transfer studies of Dy(3+)-doped fluorophosphate glasses

Dy(3+)-doped fluorophosphate glasses with composition (in mol%) (56-x/2)P(2)O(5)+17K(2)O+(15-x/2)BaO+8Al(2)O(3) + 4AlF(3)+ xDy(2)O(3), x=0.01, 0.05, 0.1, 1.0 and 2.0, have been prepared by melt quenching technique. The luminescence spectra and lifetimes of (4)F(9/2) level of Dy(3+) ions in these glasses have been measured using the 457.9 nm line of argon ion laser as an excitation source. The free-ion calculation and Judd-Ofelt analysis have been performed. The room temperature emission spectra corresponding to (4)F(9/2)-->(6)H(J) (J=7/2, 9/2, 11/2, 13/2 and 15/2) transitions of Dy(3+) ions were measured. The fluorescence decay from (4)F(9/2) level have been measured by monitoring the intense (4)F(9/2)-->(6)H(13/2) transition. The lifetime of the decay is obtained by taking the first e-folding times of the decay curves and is found to decrease with increase in Dy(3+) ions concentration due to concentration quenching. The decay curves are found to be perfectly single exponential for samples with low Dy(3+) ion concentration. The non-exponential decay curves observed for higher concentrations are well fitted to the Inokuti-Hirayama model for S=6, which indicates that the energy transfer between the donor and acceptor is of dipole-dipole nature. The energy transfer parameter and donor to acceptor interaction increases with Dy(3+) ions concentration due to increase of energy transfer from Dy(3+) (donor) to unexcited Dy(3+) (acceptor) ions.     

Investigation of concentration quenching and 1.3 microm emission in Nd(3+)-doped bismuth glasses

Nd(2)O(3)-doped 70Bi(2)O(3)-20B(2)O(3)-10SiO(2)-xNd(2)O(3) (x=0.1, 0.3, 0.5, 0.7, 1.0, 1.5 mol%) bismuth glasses were prepared by the conventional melt-quenching method, and the Nd(3+):(4)F(3/2)-->(4)I(13/2) fluorescence properties had been studied for different Nd(3+) concentrations. The Judd-Ofelt analysis for Nd(3+) ions in bismuth boron silicate glasses was also performed on the base of absorption spectrum. The transition probabilities, excited state lifetimes, the fluorescence branching ratios, quantum efficiency and the stimulated emission cross-sections of (4)F(3/2)-->(4)I(13/2) transition were calculated and discussed. Based on the electric dipole-dipole interaction theory, the interaction parameters: C(DD), for the energy migration rate (4)F(3/2), (4)I(9/2)-->(4)F(3/2), (4)I(9/2) and C(DA), for cross-relaxation rate (4)F(3/2), (4)I(9/2)-->(4)I(15/2), (4)I(15/2), and/or (4)F(3/2), (4)I(9/2)-->(4)I(13/2), (4)I(15/2) in bismuth boron silicate glasses were about 18.4 x 10(-40)cm(6)/s and 3.4 x 10(-40)cm(6)/s, respectively.     

Spectroscopic investigations of Nd(3+)-doped alkali chloroborophosphate glasses

Optical absorption spectra were studied in wavelength region 400-900 nm for the Nd(3+)-doped alkali (R = Li, Na and K) chloroborophosphate glasses at room temperature. The energy level scheme of the 4f(3) electron configuration was deduced from the observed energy level data using a parametrized Hamiltonian (H(F1)) model which includes 20 free-ion interaction parameters. Reasonable correlation was obtained between the experimental and calculated energy levels. The Judd-Ofelt model for the intensity analysis of induced electric dipole transitions has been applied to the measured oscillator strengths of the absorption bands to determine the three phenomenological intensity parameters Omega(2), Omega(4) and Omega(6) for each glass. Using these parameters, the total radiative transition rates (A(T)), non-radiative relaxation rates (W(NR)), branching ratios (beta(R)), integrated cross-sections for the stimulated emission (Sigma), excited state emission intensities (f(ESE)) and excited state absorption intensities (f(ESA)) have been theoretically calculated for certain excited Nd(3+) fluorescent levels. From the results obtained, the conclusion is made about the possibility of using these glasses as laser media.     

The spectroscopic properties of Er(3+)-doped TeO(2)-Nb(2)O(5) glasses with high mechanical strength performance

(100-x)TeO(2)-xNb(2)O(5) (x=5-20) niobic tellurite glasses doped with 0.5 mol.% Er(2)O(3) were synthesized, and their thermal, mechanical, and spectroscopic properties were measured and compared to the properties of the typical 75TeO(2)-20ZnO-5Na(2)O (TZN) tellurite glass. The refractive index (n(d)), density (rho), and glass transition temperature (T(g)) of bulk glasses increase with the Nb(2)O(5) content. The Vickers microhardness (H(v)) of bulk glass in niobic tellurite glasses also increases with the Nb(2)O(5) content. The values (2.5-3.2GPa) of H(v) in the niobic tellurite glasses are 47-88% larger than that (1.7GPa) in TZN glass. The effect of Nb(2)O(5) content on absorption spectra, the Judd-Ofelt parameters Omega(t) (t=2, 4, 6), fluorescence spectra and the lifetimes of Er(3+):I(13/2) level were also investigated, and the stimulated emission cross-section was calculated from McCumber theory. With increasing Nb(2)O(5) content in the glass composition, the Omega(t) (t=2, 4, 6) parameters, fluorescence full width at half maximum (FWHM) of I(13/2) of Er(3+) increase, while the (4)I(13/2) lifetimes of Er(3+) decreases. Compared with TZN glass, the gain bandwidth properties of Er(3+)-doped TeO(2)-Nb(2)O(5) glass is much larger than in tellurite glass based TeO(2)-ZnO-Na(2)O system, bismush-based glass, germanate, and silicate glasses, which indicates that TeO(2)-Nb(2)O(5) glasses are better choice as a practical available host material for broadband Er(3+)-doped amplifier.     

Study of luminescence properties of novel Er3+ single-doped and Er3+/Yb3+ co-doped tellurite glasses

The novel Er(3+) single-doped and Er(3+)/Yb(3+) co-doped tellurite glasses were prepared. The effect of Yb(2)O(3) concentration on absorption spectra, emission spectra and upconversion spectra of glasses were measured and investigated. The emission intensity, fluorescence full width at half maximum (FWHM) and upconversion luminescence of Er(3+) go up with the increasing concentration of Yb(3+) ions. The maximum FWHM of (4)I(13/2) --> (4)I(15/2) transition of Er(3+) is approximate 77 nm for 1.41 x 10(21)ions/cm(3) concentration of Yb(3+)-doped glass. The visible upconversion emissions at about 532, 546 and 659 nm, corresponding to the (2)H(11/2) --> (4)I(15/2), (4)S(3/2) --> (4)I(15/2) and (4)F(9/2) --> (4)I(15/2) transitions of Er(3+), respectively, were simultaneously observed under the excitation at 970 nm. Subsequently, the possible upconversion mechanisms and important role of Yb(3+) on the green and red emissions were discussed and compared. The results demonstrate that this kind of tellurite glass may be a potentially useful material for developing potential amplifiers and upconversion optical devices.     

Spectroscopic characteristics of Sm3+-doped alkali fluorophosphate glasses

Optical absorption, luminescence and lifetime measurements of Sm(3+)-doped alkali fluorophosphate glasses with molar compositions of 50(NaPO(3))(6)+10TeO(2)+20AlF(3)+19RF+1Sm(2)O(3) (R=Li, Na and K) are described. The variation of optical properties with glass composition plays a dominant role in the determination of efficient laser materials. From the experimental oscillator strengths of f-f electric dipole transitions, the phenomenological Judd-Ofelt parameters have been evaluated and are used to evaluate radiative parameters such as radiative transition probabilities (A(R)), branching ratios (beta(R)), lifetimes (tau(R)) and integrated absorption cross-section (sigma(a)) for various excited levels. The predicted values of tau(R) and beta(R) from the (4)G(5/2) excited level to its lower levels are compared with the experimentally measured values. Stimulated emission cross-sections (sigma(e)) were also determined for (4)G(5/2)-->(6)H(J) (J=5/2, 7/2, 9/2 and 11/2) emission transitions. From the emission transitions of Sm(3+) in these alkali tellurofluorophosphate glasses certain potential laser transitions have been identified.     

Optical characterization of Sm3+ and Dy3+:ZnO-PbO-B2O3 glasses

Here, we present the results of the analysis of Sm(3+) or Dy(3+) (0.5 mol%) ions doped heavy metal oxide (HMO)-based zinc lead borate (ZLB) glasses. Optical measurements such as absorption, emission spectra, lifetimes, XRD, DSC profiles have been carried out. The emission spectrum of Sm(3+):ZLB has shown the emission transitions of (4)G(5/2)-->(6)H(5/2) (563 nm), (4)G(5/2)-->(6)H(7/2) (598 nm), (4)G(5/2)-->(6)H(9/2) (646 nm), (4)G(5/2)-->(6)H(11/2) (708 nm) with lambda(exc): 401 nm ((6)H(5/2)-->(4)F(7/2)). In the case of the Dy(3+):ZLB glass, emission transitions of (4)F(9/2)-->(6)H(15/2) (485 nm), (4)F(9/2)-->(6)H(13/2) (575 nm) and (4)F(9/2)-->(6)H(11/2) (664 nm) with lambda(exi): 447 nm ((6)H(15/2)-->(4)I(15/2)) have been identified. Energy level schemes relating to the emission mechanisms involved in Sm(3+) and Dy(3+) glasses have been given.     

Spectroscopic investigations of Nd3+ doped flouro- and chloro-borate glasses

Spectroscopic and physical properties of Nd(3+) doped sodium lead flouro- and chloro-borate glasses of the type 20NaX-30PbO-49.5B(2)O(3)-0.5Nd(2)O(3) (X=F and Cl) have been investigated. Optical absorption spectra have been used to determine the Slater Condon (F(2), F(4), and F(6)), spin orbit xi(4f) and Racah parameters (E(1), E(2), and E(3)). The oscillator strengths and the intensity parameters Omega(2), Omega(4) and Omega(6) have been determined by the Judd-Ofelt theory, which in turn provide the radiative transition probability (A), total transition probability (A(T)), radiative lifetime (tau(R)) and branching ratio (beta) for the fluorescent level (4)F(3/2). The lasing efficiency of the prepared glasses has been characterized by the spectroscopic quality factor (Omega(4)/Omega(6)), the value of which is in the range of 0.2-1.5, typical for Nd(3+) in different laser hosts. Nephelauxetic effect results in a red shift in the energy levels of Nd(3+) for chloroborate glass. The radiative transition probability of the potential lasing transition (4)F(3/2)-->(4)I(11/2) of Nd(3+) ions is found to be higher for flouroborate as compared to chloroborate glass.     

Thermal stability and spectroscopic properties of Er3+-doped antimony-borosilicate glasses

This paper reports on the optical spectroscopic properties and thermal stability of Er(3+)-doped antimony-borosilicate glasses for developing 1.5mum optical amplifiers. Upon excitation at 980nm laser diode, an intense 1.5mum infrared fluorescence has been observed with the maximum full width at half maximum (FWHM) of 90nm for Er(3+)-doped antimony-borosilicate glasses. The emission cross-section and the lifetime of the (4)I(13/2) level of Er(3+) ions are 6.3x10(-21)cm(2) and 0.30ms, respectively. It is noted that the product of the emission cross-section and FWHM of the glass studied is as great as 567x10(-21)cm(2)nm, which is comparable or higher than that of bismuthate and tellurite glasses.     

Laser-diode-excited intense luminescence and green-upconversion in erbium-doped bismuth-germanate-lead glasses

We investigate the spectroscopic properties of the 1.5-microm emission from the (4)I(13/2)-->(4)I(15/2) transition of Er(3+) ions in bismuth-germanate-lead glasses for applications in broadband fiber amplifiers. The emission peak locates at 1532nm with a full width at half-maximum (FWHM) of approximately 65nm. The measured lifetime and the calculated emission cross-section of this transition are 3.3ms and 8.66x10(-21)cm(2), respectively. IR-to-green-upconversion occurs simultaneously upon excitation of the 1.5-microm emission with a commercially available 980nm laser diode. Effects of PbF(2) content on the thermal stability, structure and spectroscopic properties of Er(3+)-doped bismuth-germanate-lead glasses have been examined. We find that the substitution with PbF(2) provides a couple of potentials: shortening the UV cutoff band and decreasing the phonon energy of host glasses. Codoping of Yb(3+) significantly enhances both the green-upconversion and 1.5-microm emission intensity by means of a nonradiative Yb(3+)-->Er(3+) energy transfer. Energy transfer processes and nonradiative phonon-assisted decays could account for the population of the (2)H(11/2) level, which is an emitting level of the green-upconversion of Er(3+). The results indicate the possibility towards the development of bismuth-germanate-lead based glasses as photonics devices.     

Effect of fluorine ions on 2.7 μm emission in Er3+/Nd(3+)-codoped fluorotellurite glass

The 2.7 μm emission properties of Er(3+)/Nd(3+)-codoped fluorotellurite glasses were investigated in the present work. The thermal stability, refractive index, absorption and transmission spectra, and emission spectra were measured and investigated. The 2.7 μm emission in Er(3+)/Nd(3+)-codoped fluorotellurite glasses was enhanced with the increase of fluorine ions. The Judd-Ofelt analysis based on absorption spectra was performed in order to determine the Judd-Ofelt intensity parameters Ωt (t = 2, 4, 6), spontaneous emission probability, radiative lifetime and branching ratios of Er(3+):(4)I(11/2) → (4)I(13/2) transition. It is found that the Er(3+)/Nd(3+)-codoped fluorotellurite glass possesses a lower spontaneous transition probability A (58.95 s(-1)) but a higher branching ratio β (15.72%) corresponding to the stimulated emission of Er(3+):(4)I(11/2) → (4)I(13/2) transition. Additionally, the transmittance was also tested and reached a maximum when the molar concentration of ZnF(2) is 15%. The presence of fluorine ions greatly decreases the population of OH(-) groups, which affects the 2.7 μm emission effectively by means of decreasing the rate of energy transfer to impurities (e.g., OH(-) groups).     

Optical characterization of Eu3+ and Tb3+ ions doped zinc lead borate glasses

This paper reports on the spectral analysis of Eu3+ or Tb3+ ions (0.5 mol%) doped heavy metal oxide (HMO) based zinc lead borate glasses from the measurement of their absorption, emission spectra and also different physical properties. From the XRD, DSC profiles, the glass nature and glass thermal properties have been studied. The measured emission spectrum of Eu3+ glass has revealed five transitions (5D0-->7F0, 7F1, 7F2, 7F3 and 7F4) at 578, 591, 613, 654 and 702 nm, respectively, with lambdaexci=392 nm (7F0-->5L6). In the case of Tb3+:ZLB glass, four emission transitions such as (5D4-->7F6, 7F5, 7F4 and 7F3) that are located at 489, 542, 585 and 622 nm, respectively, have been measured with lambdaexci=374 nm. For all these emission bands decay curves have been plotted to evaluate their lifetimes and the emission processes that arise in the glasses have been explained in terms of energy level schemes.     

Effect of Ga2O3 on the spectroscopic properties of erbium-doped boro-bismuth glasses

The spectroscopic properties and thermal stability of Er3+-doped Bi2O3-B2O3-Ga2O3 glasses are investigated experimentally. The effect of Ga2O3 content on absorption spectra, the Judd-Ofelt parameters Omega t (t=2, 4, 6), fluorescence spectra and the lifetimes of Er3+:4I 13/2 level are also investigated, and the stimulated emission cross-section is calculated from McCumber theory. With the increasing of Ga2O3 content in the glass composition, the Omega t (t=2, 4, 6) parameters, fluorescence full width at half maximum (FWHM) and the 4I 13/2 lifetimes of Er3+ first increase, reach its maximum at Ga2O3=8 mol.%, and then decrease. The results show that Er3+-doped 50Bi2O3-42B2O3-8Ga2O3 glass has the broadest FWHM (81nm) and large stimulated emission cross-section (1.03 x1 0(-20)cm2) in these glass samples. Compared with other glass hosts, the gain bandwidth properties of Er+3-doped Bi2O3-B2O3-Ga2O3 glass is better than tellurite, silicate, phosphate and germante glasses. In addition, the lifetime of 4I 13/2 level of Er(3+) in bismuth-based glass, compared with those in other glasses, is relative low due to the high-phonon energy of the B-O bond, the large refractive index of the host and the existence of OH* in the glass. At the same time, the glass thermal stability is improved in which the substitution of Ga2O3 for B2O3 strengthens the network structure. The suitability of bismuth-based glass as a host for a Er3+-doped broadband amplifier and its advantages over other glass hosts are also discussed.     

Spectroscopic properties of Er(3+)/Yb(3+) co-doped Bi(2)O(3)-B(2)O(3)-GeO(2) glasses

Er(3+)/Yb(3+) co-doped 60Bi(2)O(3)-(40 - x)B(2)O(3)-xGeO(2) (BBG; x=0, 5, 10, 15 mol%) glasses that are suitable for fiber lasers, amplifiers have been fabricated and characterized. The absorption spectra, emission spectra, and lifetime of the (4)I(13/2) level and quantum efficiency of Er(3+):(4)I(13/2) --> (4)I(15/2) transition were measured and calculated. With the substitution of GeO(2) for B(2)O(3), both Delta lambda(eff) and sigma(e) decrease from 75 to 71 nm and 9.88 to 8.12 x 10(-21) cm(2), respectively. The measured lifetime of the (4)I(13/2) level and quantum efficiency of Er(3+):(4)I(13/2) --> (4)I(15/2) transition increase from 1.18 to 1.5 ms and 36.2% to 43.2%, respectively. The emission spectra of Er(3+):(4)I(13/2) --> (4)I(15/2) transition was also analyzed using a peak-fit routine, and an equivalent four-level system was proposed to estimate the stark splitting for the (4)I(15/2) and (4)I(13/2) levels of Er(3+) in the BBG glasses. The results indicate that the (4)I(13/2) --> (4)I(15/2) emission of Er(3+) can be exhibit a considerable broadening due to a significant enhance the peak A, and D emission.     

Up-conversion luminescence analysis in ytterbium-sensitized erbium-doped oxide-halide tellurite and germanate-niobic-lead glasses

Ytterbium-sensitized erbium-doped oxide-halide tellurite and germanate-niobic-lead glasses have been synthesized by conventional melting method. Intense green and red emissions centered at 525, 546 and 657 nm, corresponding to the transitions 2H11/2-->4I15/2, 4S3/2-->4I15/2 and 4F9/2-->4I15/2, respectively, were simultaneously observed at room temperature in these glasses. The quadratic dependence of the 525, 546 and 657 nm emissions on excitation power indicates that a two-photon absorption process occurs. Tellurite glass showed a weaker up-conversion emission than germanate-niobic-lead glass, which is inconsistent with the prediction from the difference of maximum phonon energy between tellurite and germanate-niobic-lead glasses. In this paper, Raman spectroscopy was employed to investigate the origin of the difference in up-conversion luminescence in the two glasses. Compared with phonon side-band spectroscopy, Raman spectroscopy extracts more information including both phonon energy and phonon density. Our results reveal that the phonon density and the maximum phonon energy of host glasses are both important factors in determining the up-conversion efficiency.     

Preparation process and upconversion luminescence of Er3+-Doped glass ceramics containing Ba2LaF7 nanocrystals

The preparation process and upconversion luminescence of the Er(3+)-doped glass ceramics containing Ba(2)LaF(7) nanocrystals were investigated. The formation of Ba(2)LaF(7) nanocrystals in the glass ceramics was confirmed by X-ray diffraction. Er(3+)-doped glass ceramics containing Ba(2)LaF(7) nanocrystals exhibited highly efficient upconversion luminescence in comparison with glasses. With the increase of heat treatment temperature the upconversion luminescence intensity increased gradually. The composition of glasses was also found to have significant influence on the crystallization process of glass ceramics. The mixture of Ba(2)LaF(7) and La(2)O(3) nanocrystals and the mixture of La(2)F(3) and La(2)O(3) nanocrystals in the glass ceramics could be obtained by controlling different compositions of glasses. The upconversion luminescence intensity also varied significantly with different nanocrystals in the glass ceramics.     

Spectroscopic properties and thermal stability of Er3+ -doped TeO2-B2O3-Nb2O5-ZnO glass for potential WDM amplifier

A series of novel 70TeO2-(15-x)B2O3-xNb2O5-15ZnO-1wt.% Er2O3 (TBN x=0, 3, 6, 9, 12 and 15 mol%) tellurite glasses were prepared. The thermal stability, absorption spectra, emission spectra, and the lifetime of the (4)I(13/2) level of Er(3+) ions were measured and investigated. Three Judd-Ofelt intensity parameters Omega(t) (t=2, 4 and 6) (Omega(2)=(5.42-6.76)x10(-20)cm(2); Omega(4)=(1.37-1.73)x10(-20)cm(2); Omega(6)=(0.70-0.94)x10(-20)cm(2)) of Er(3+) ions were calculated by Judd-Ofelt theory. It is found that the Omega(6) first increases with the increase of Nb2O5 content from 0 to 6 mol% and then decreases, which is mainly affected by the number of non-bridging oxygen ions of the glass network. The high peak of stimulated emission cross-section (sigma(e)(peak)=(0.77-0.91)x10(-20)cm(2)) of Er(3+): (4)I(13/2)-->(4)I(15/2) transition were obtained according to McCumber theory and broad full width at half maximum (FWHM=65-73 nm) of the (4)I(13/2)-->(4)I(15/2) transition of Er(3+) ions were measured. The results indicate that these new TBN glasses can be used as a candidate host material for potential broadband optical amplifiers.     

Spectroscopic properties of Dy(3+) ions in NaF-B(2)O(3)-Al(2)O(3) glasses

This paper reports the optical properties of Dy(3+) in sodium fluoroborate glasses of the type XNaF.(89-X)B(2)O(3).10 Al(2)O(3).1Dy(2)O(3) (where X=8, 12, 16, 20 and 24). Judd-Ofelt intensity parameters (Omega(2), Omega(4), Omega(6)) are derived from the absorption spectra. The Judd-Ofelt theory has been applied to interpret the local environment of Dy(3+) ions and bond covalency of RE-O bond. These parameters have been used to calculate radiative transition probabilities (A(rad)), lifetimes (tau(R)) and branching ratios (beta(R)) for the excited level (4)F(9/2). The predicted values of tau(R) are compared with the measured values for (4)F(9/2) level for five glass compositions (Glass (A-E)). The stimulated emission cross-section sigma(lambda(P)) are also evaluated for the (4)F(9/2)-->(6)H(J) (J=11/2, 13/2, and 15/2) transitions.     

Spectra analysis of Nd(DBM)3(TPPO)2 in MMA solution and PMMA matrix

The absorption spectra of Nd(DBM)3(TPPO)2 (DBM = dibenzoylmethane; TPPO = triphenylphosphine oxide) in methyl methacrylate (MMA) and polymethyl methacrylate (PMMA) were measured. Slater-Condon parameters (F2, F4, F6), Lander parameter (zeta4f), nephelauxetic effect parameters (beta, delta) and Judd-Ofelt parameters (Omega2, Omega4, Omega6) were calculated on the basis of the absorption spectra. Analysis of the relationship between the structure of rare-earth complexes and the nephelauxetic effect, Judd-Ofelt parameter Omega2 was carried out. The radiative properties of Nd(DBM)3(TPPO)2 in PMMA were also predicted according to the Judd-Ofelt theory. The values of the radiative lifetime and the emission cross-section of 4F3/2 --> 4I11/2 fluorescence transition are comparable with those shown by glasses used in the solid-state laser applications.     

Study of upconversion fluorescence property of novel Er3+/Yb3+ co-doped tellurite glasses

Er3+/Yb3+ co-doped TeO2-B2O3-Nb2O5-ZnO (TBN) glasses were prepared. The absorption spectra and upconversion luminescence spectra of TBN glasses were measured and analyzed. The upconversion emission bands centered at 530, 546 and 658 nm were observed under the excitation at 975 nm, corresponding to the transitions of 2H11/2-->4I15/2, 4S3/2-->4I15/2 and 4F9/2-->4I15/2 respectively. The ratio of red emission to green emission increases with an increasing of Yb3+ ions concentration. According to the quadratic dependence on excitation power, the possible upconversion mechanisms and processes were discussed.