McCumber Theory Research Articles

Er3+-doped SiO2-based glasses – An exploration of structural, visible, chromatic, and NIR fluorescence characteristics

SiO2-based glasses doped with 1 mol% Er3+ were fabricated via melt-quench process and their structural and visible and NIR (near-infrared) fluorescence features have been investigated. Calculated Judd–Ofelt (J–O) intensity parameters that were deduced from absorption spectra are applied to reckon different radiative factors. Visible emission spectra and decay profiles (for 4S3/2 → 4I15/2 transition) were registered upon λexci.= 379 nm. CIE (Commission International de I'Eclairage), CCT (correlated color temperature), and CP (color purity) values were evaluated from the emission spectra. Also, a NIR luminescence band (4I13/2 → 4I15/2 transition) was identified by 980 nm LD (laser diode). Later, emission cross-section [(σemi) stimulated, (σMemi) from Mccumber theory] values were computed for observed NIR emission. Highest σemi and gain bandwidth (σemi × ∆λeff) were obtained to be 9.18×10−21 cm2 and 517×10−28 cm3 accordingly for 4I13/2 → 4I15/2 transition.

1.53 μm luminescent properties of Er3+-doped fluoroaluminate glasses

The Er3+ doped fluoroaluminate glasses were prepared by melt quenching technique and characterized through spectroscopic methods. The concentration of erbium ions was 0.1, 0.5 and 1.0 mol %. Luminescence spectra with a maximum of about 1.53 μm were obtained with excitation at a wavelength of 975 nm. Based on measurements in the integral sphere, it was found that with an increase in the concentration of erbium ions, the intensity of the luminescence band increases. The absorption (4I15/2 → 4I13/2) and emission (4I13/2 → 4I15/2) cross-sections were calculated using McCumber theory. The peak value of emission cross-section was 5.30 × 10−21 cm2 and the gain bandwidth value was 243 × 10−28 cm2. The calculated gain/loss spectra at different population inversion values suggest that, the fluoroaluminate glasses possess amplification in C and L spectral bands starting from 45% population inversion. The obtained results reveal that glasses of investigated composition are candidates for optical fiber amplifiers and laser sources operated at 1.5 μm.

Praseodymium mid-infrared emission in AlF3-based glass sensitized by ytterbium.

Broadband emission was obtained over 2.6 to 4.1 μm (Pr3+: 1G4→3F4, 3F3) in AlF3-based glass samples doped with different concentrations of praseodymium and 1 mol% ytterbium using a 976 nm laser pump. An efficient energy transfer process from Yb3+: 2F5/2 to Pr3+: 1G4 was analyzed through emission spectra and fluorescence lifetime values. The absorption and emission cross-sections were calculated by Füchtbauer-Ladenburg and McCumber theories and a positive gain can be obtained when P>0.3. To the best of the authors' knowledge, this work represents the first report of broadband mid-infrared emission of Pr3+ in an AlF3-based glass. The results show that praseodymium doped AlF3-based glass sensitized by ytterbium could be a promising candidate for fiber lasers operating in mid-infrared region.

Investigation of spectroscopic and photoluminescence properties of Erbium doped phosphate (P2O5-K2O3-Al2O3) glasses

Erbium (Er) doped P2O5-K2O3-Al2O3:Er2O3 glasses (KPEr) with different contents of Er3+ ions were fabricated by famous melt-quenching technique. The fabricated samples were characterized by using physical, X-ray photoelectron spectroscopy (XPS), photoluminescence, absorption, and J-O analysis techniques. The XRF analyses were performed in order to know the change in elemental composition of fabricated glasses, while using the various concentrations of Er3+ ions. Three emission peaks were observed, two peaks in visible regions of 526 nm (2H11/2→4I15/2) and 550 nm (4S3/2→4I15/2) and one peak in near infrared (NIR) region of 1545 nm (4I13/2→4I15/2). Nine peaks were observed in absorption spectra in the range of 390–1800 nm. The trend of JO parameters for the present KPEr6 glass sample is Ω2> Ω4> Ω6. Higher values of stimulated emission cross-section σemi(λ), full wave half maxima FWHM and (FWHM x σemi (λ)), for KPEr6 indicate that the present glass has potential candidate to be used for broadband amplification in telecommunication. The McCumber theory is used to study absorption and emission cross-section for 4I13/2→4I15/2 transition. The luminescence colors of these samples were almost entirely fall in the yellow-green (Y-G) region (x = 0.33, y = 0.64) in the CIE 1931 diagram. The calculated CCT values for our prepared glasses were found to be 5554 K. The present study suggest that KPEr glass samples have potential candidate for broadband amplification in telecommunication, green LED and display devices.

3.9 µm emission in Nd3+ sensitized Ho3+ doped fluoroaluminate glasses

Ho3+ and Nd3+/Ho3+ doped fluoroaluminate glass samples were fabricated by the melt-quenching method and showed high transmittance and a wide transparency window. Under 808 nm pumping, emission at 3.9 µm, corresponding to the Ho: 5I5→5I6 transition, was observed. The presence of Nd3+ strongly enhances the Ho3+ emission. The emission and absorption cross-sections were calculated using the Judd-Ofelt, Füchtbauer-Ladenburg and McCumber theories and the energy transfer mechanism between Nd3+ and Ho3+ was analyzed. The most efficient 3.9 µm emission was obtained when the concentration ratio of Nd3+: Ho3+ is 1: 2.

Efficient 3.5 μm mid-infrared emission in heavily Er3+-doped fluoroaluminate glasses and its emission mechanism

Er3+-doped fluoroaluminate glasses with different concentrations were prepared by using melt-quenching method. Under a 638 nm laser diode pumping, efficient 3.5 μm emission was observed in the 18 mol% Er3+ doped sample, which was ascribed to the Er3+: 4F9/2 → 4I9/2 transition. The fluorescence properties such as radiative transition probability, energy level lifetime and branch ratio were predicted by the well-known Judd-Ofelt theory, while the emission and absorption cross-sections were calculated using the Füchtbauer-Ladenburg and McCumber theories, respectively. Both simulated and experimental results show that Er3+-doped fluoroaluminate material is a promising gain medium for 3.5 μm laser applications.

Spectroscopic study of Er3+ doped borate glass system for green emission device, NIR laser, and optical amplifier applications

The 10BaO–20ZnO–20LiF-(50-x)B2O3-xEr2O3 (x = 0, 0.1, 0.5, 0.7, and 1.0 mol %) glass system was studied for green emission device, NIR laser, and optical amplifier applications. The impact of Er3+ doping was assessed through structural, optical, and thermal properties. The Er3+ ions behaved as network modifiers and decreased the network rigidity by the transformation of [BO4]→[BO3] and Non-Bridging Oxygens. This was consistent with the decrease in the glass transition temperature. Ten absorption peaks of Er3+ ion equivalent to transitions from 4I15/2 to various excited levels were quantified through their oscillator strengths. Through broadband impedance spectroscopy, the insulating property of the glass system was authenticated by the persistence of dc-conductivity in the order of 10−10 Scm−1 up to 523 K. With 378 nm excitation, a violet emission (2H9/2→4I15/2) and two intense green emissions (2H11/2→4I15/2, 4S3/2→4I15/2) were noticed. The NIR emission (4I13/2→4I15/2) was observed at 1531 nm with 378 and 980 nm excitations and the corresponding decay curves were recorded. The Inokuti-Hirayama model indicated the increase in the energy transfer and reduction in critical distance amid the Er3+ ions with doping leading to energy migration through cross-relaxations and lifetime quenching. The laser parameters were determined from Fuchtbauer-Ladenburg theory. The color coordinates of the samples were lying in the green region, with purity >89% and CCT >6000 K. The gain coefficient from McCumber theory was positive for a population inversion >50%, with a wide gain between 1460 and 1565 nm, extending the application of the glass system as an optical amplifier in the S + C communication window.

Ytterbium-doped chloride photo-thermo-refractive glass: spectral, luminescent, and gain properties

We developed a new chloride photo-thermo-refractive glass doped with ytterbium ions. The dependence of optical and spectral-luminescent characteristics on ytterbium concentration has been studied. Concentration dependence of excited state decay time has been analyzed taking into account the self-trapping and self-quenching mechanisms. The optimum concentration of ytterbium ions in chloride photo-thermo-refractive glass has been determined. Other important spectroscopic parameters such as absorption and emission cross-sections, radiative lifetimes, pump saturation, and minimum pump intensities have been obtained using absorption and emission measurements and theoretical approaches such as Fuchtbauer-Landenburg and McCumber theories. The evolution of the gain cross-section spectrum as a function of a population inversion parameter has been performed. Results of this study show that the ytterbium-doped chloride photo-thermo-refractive glass demonstrates good spectroscopic and luminescent properties for laser and gain application.

Pre-assessments of optical transition, gain performance and temperature sensing of Er3+ in NaLn(MoO4)2 (Ln = Y, La, Gd and Lu) single crystals by using their powder-formed samples derived from traditional solid state reaction

Rare earth doped molybdate single crystals are excellent laser working media. The growths of molybdate single crystals are money-cost and time-consuming. It would be preferable if the spectroscopic properties and laser performance of the laser crystals could be pre-assessed before their growths. In this work, we proposed a route to pre-assess the spectroscopic properties, gain performance and temperature sensing effects for the rare earth doped molybdate single crystals by using the powder-formed rare earth doped molybdate phosphors. The route we proposed was applied for assessing the Er3+ doped NaLn(MoO4)2 (Ln = Y, La, Gd and Lu) crystals by using the corresponding molybdate phosphors which were prepared via a solid state reaction. The optical transition properties of Er3+ in these molybdates were studied in the framework of Judd-Ofelt theory by using the diffuse-diffraction spectra. The radiative transition rates, fluorescence branching ratios and radiative lifetimes were further confirmed and compared for all studied Er3+ doped molybdates. Furthermore, the absorption cross sections, emission cross sections and optical gain coefficient spectra for the interested transitions of Er3+ in the molybdates were also determined via Füchtbauer-Ladenburg formula and McCumber theory. Meanwhile, the laser gain performance for the studied molybdate laser crystals was also assessed and compared with each other. A route for advanced heat management for the laser devices was proposed as well, and the temperature detection performance of the molybdates was also evaluated. This study proves that the pre-assessments for the rare earths doped laser single crystals by using their corresponding easy-prepared phosphors are workable.

Spectroscopic investigations on 1.53 μm NIR emission of Er3+ doped multicomponent borosilicate glasses for telecommunication and lasing applications

The multicomponent borosilicate (MBSER) glasses activated with different concentrations of Er3+ ions (varies from 0.1 to 2 mol%) were prepared via conventional melting and rapid quench technique and studied their thermal, structural and spectroscopic characteristics by using DSC, XRD, FTIR, optical absorption, excitation and emission measurements. Judd- Ofelt analysis in correlation with the absorption and emission spectral profiles was performed for the evaluation of several radiative parameters of the as-prepared glasses. Visible and NIR luminescence were recorded at 379 nm excitation and a special consideration is given to 1536 nm emission corresponding to the 4I13/2 → 4I15/2 transition. McCumber theory (MC) is used to determine the stimulated emission cross-section from the calculated absorption cross-section and is found well matched with the emission cross-section obtained from Fuchtbauer-Ladenburg (FL) equation. Better radiative parameters (stimulated emission cross-section (σemi) = 15.78 × 10−21cm2, effective bandwidth (Δλeff) = 67 nm), laser (gain bandwidth (σ(λp) x Δλeff = 1.05 × 10−25 cm3), optical gain (σ(λp) x τR) = 42.5 × 10−25 cm2s)) and gain spectra characteristics suggests the MBSER glasses for optical amplifier and laser applications since they offer a broadened emission spectra in the NIR region.

Comparative Study of Er3+ Ions Doped Phosphate Based Oxide and Oxy-fluoride Glasses for Lasers Applications

Abstract Er3+ ions doped sodium strontium gadolinium oxide and oxy-fluoride phosphate glass samples prepared by conventional melt quenching technique. The samples were melted at 1200 °C in electric furnace with alumina crucibles. The densities of the samples were measure with the help of Archimedes principle using water as immersion liquid. The refractive index (n) was measured by Abbe refractometer with a sodium-vapour lamp as a light source and using mono-bromonaphthalene (C10H7Br) as a contact liquid. The prepared glass samples were characterized with UV-Vis-NIR absorptions and NIR photoluminescence. The UV-Vis-NIR spectra show peaks at 379, 406, 488, 521, 548, 652, 803, 977, and 1536 nm which are due to the transitions from 4 I15/2 ground state to 2H9/2, 4F3/2, 4F7/2, 4H11/2, 4S3/2, 4F9/2, 4I11/2 and 4I13/2 exited states of Er3+ ions, respectively. In NIR emission one broad peak at 1543 nm is observed in present glass samples with 379 nm excitation. From NIR emission it is observed that the FFEr glass give better emission intensity than the GEr and FEr. McCumber theory was used to evaluate stimulated emission cross-section of 4I13/2→4I15/2 transition of Er3+ ion using the absorption spectral measurements. Thus, these results show that present glasses have the potential for use in efficient short and conventional-length optical amplifiers and tuneable lasers

Dissipation processes in superconducting NbN nanostructures

In this paper, we present a comprehensive study of electrical transport measurements on a superconducting film of NbN (thickness, d ∼ 50 nm) and its nanostructures fabricated using Focused Ion Beam (FIB) in the form of one bridge (width, w ∼ 50 µm) and three meanders (w ∼ 500 nm, 250 nm, and 100 nm). The resistance (R) and current–voltage [V(I)] characteristics are measured as a function of temperature (2 K–16 K) and magnetic field (0 T–7 T). The photoresponse is measured under quasi-monochromatic light irradiation (wavelength of ∼800 nm). All our samples with w ≫ ξ and d > ξ are dimensionally on the borderline of the three-dimensional limit. However, the film and bridge samples show quasi-2D signatures of Brzezinski–Kosterlitz–Thouless transition in the R(T) and V(I) characteristics. On the other hand, our meander samples show two slope transitions in R(T) that seem to fit well with the thermally activated phase slip (TAPS) near the superconducting onset and quantum phase slip (QPS) at lower temperatures, expected in quasi-1D superconductors. The presence of TAPS and QPS in all the meander samples is further supported by several other observations at B = 0: (i) linear V(I) at lower excitation currents in the entire transition region; (ii) nonlinear and non-hysteretic V(I) at higher currents in the TAPS region; (iii) in the QPS region, at higher currents, the V(I) curves show a quadratic V ∝ I2 dependence before hysteretic and stepped jumps; and (iv) the switching current (IC*) reduces significantly to 5 μA–25 μA (T = 2 K) when compared to nearly ∼875 μA (T = 10.5 K) in the bridge sample. With the application and increase in the magnetic field, at fixed temperatures in the QPS region of the meander samples, the V(I) characteristics show a crossover to TAPS. This seems to be correlated with a drastic reduction in the activation barrier (Ub) extracted from the R(T,B) data. Typically, for B = 0 T–7 T, Ub varies from ∼3000 K–1200 K (film sample) to ∼1100 K–220 K (bridge sample) and ∼250 K–50 K, ∼150 K–20 K, and ∼50 K–6 K for the 500 nm, 250 nm, and 100 nm meander samples, respectively. Using the Langer, Ambegaokar, McCumber, and Halperin theory [J. S. Langer and V. Ambegaokar, Phys. Rev. 164(2), 498 (1967); D. E. McCumberand B. I. Halperin, Phys. Rev. B 1, 1054 (1970)] and considering the normal state transport properties reported earlier [Joshi et al., AIP Adv. 8, 055305 (2018)], these results are shown to be consistent with disorder induced nano-paths of ∼50 nm, ∼12 nm, ∼10 nm, and ∼7 nm width developed in the FIB fabricated bridge and 500 nm, 250 nm, and 100 nm meander samples, respectively.

Er3+/Yb3+ co-doped bismuthate glass and its large-mode-area double-cladding fiber for 1.53 μm laser

Er3+/Yb3+ co-doped large-mode-area double-cladding fibers based on Bi2O3-GeO2-Ga2O3–Na2O–CeO2 glass material were fabricated using a rod-in-tube method. Due to the low core numerical aperture (NA = 0.057), the prepared fiber can operate in single-mode regime with a cut-off wavelength of ∼1.49 μm while its core diameter reaches 20 μm. Based on the measured absorption spectrum, the spectroscopic parameters of Er3+/Yb3+ co-doped core glass were calculated by Judd-Ofelt theory. Relatively large spectroscopic quality factor (χ = 3.139), spontaneous transition probability (266.58 s−1) and radiative lifetime (3.75 ms) indicate the core glass has good radiation characteristics. Moreover, under 980 nm excitation, the strongest 1.53 μm emission is achieved in core glass while the doping concentration ratio of Er3+/Yb3+ is 1.0 mol%: 2.5 mol%. And the maximum emission cross section is calculated to be 8.2 × 10−21 cm2 at 1532 nm by McCumber theory. Finally, a stable laser output at 1535.4 nm is achieved in a 50 cm long as-drawn Er3+/Yb3+ co-doped fiber, yielding a maximum laser output power of 93.64 mW and a slope efficiency of 11.75%. The excellent optical properties indicate the prepared Er3+/Yb3+ co-doped fibers have potential applications for 1.53 μm band high power fiber laser.

Erbium spectral-luminescent characteristics in bromide-fluoride photo-thermo-refractive glasses

Subject of Research. The paper presents the study of spectral-luminescent characteristics of erbium ions in bromide- fluoride photo-thermo-refractive glasses with 0.1 mol% of erbium oxide and 1-2 mol% of ytterbium oxide concentration. Such spectroscopic parameters as stimulated emission cross-section of erbium ions at a wavelength of 1.5 microns, the efficiency of energy transfer from ytterbium to erbium ions, and the quantum efficiency are calculated based on the measured absorption spectra of glasses under study. The gain/loss spectra of erbium ions in the infra-red range are calculated for various population inversion values. Methods. Bromide-fluoride photo-thermo-refractive glasses were synthesized in an electric furnace at the temperature of 1480 °C for 5 hours in the air. Judd-Ofelt theory was used for determination of spectroscopic intensity parameters. The amplification spectra were obtained using McCumber theory. Main Results. It was found that the stimulated emission cross-section of erbium ions at a wavelength of 1.5 microns is typical for erbium in silicate glasses. The quantum efficiency of radiation at the same wavelength reached 95 %, and the energy transfer efficiency was 86 %. The gain factor had a positive value when the population inversion parameter was higher than 0.5. Practical Relevance. Bromide-fluoride photo-thermo-refractive glasses activated with erbium and ytterbium ions have spectral-luminescent characteristics comparable with commercial laser silicate glasses. In addition, they allow for recording of highly efficient Bragg gratings. Thus, these glasses can be promising candidates for creating distributed feedback lasers with ultra-narrow spectral lines.

Concentration effect of Yb3+ ions on the spectroscopic properties of high-concentration Er3+/Yb3+ co-doped phosphate glasses

High-concentration erbium-ytterbium (Er3+/Yb3+) co-doped phosphate glasses were manufactured by the melt-quenching method. The phosphate glass matrix was 58.5P2O5–11K2CO3–11BaCO3–7Al2O3–2ZnO-0.5Er2O3-xYb2O3 (x = 10, 11, 12, and 13 mol%). Various spectroscopic parameters of glasses were measured as a function of the matrix composition, temperature control, dehydration and the Er3+/Yb3+ concentration to evaluate the potential of these glasses to act as a laser material for the eye-safe laser emission (1.53 μm). The density, refractive index, glass-transition temperature, and softening temperature increase gradually with the increase of Yb3+ concentration. The glass sample with 12 mol% Yb2O3 did not show devitrification even when the temperature reached 850 °C. The optimized Er3+/Yb3+ ratio of 0.5/12, gives the highest luminescence intensity at 1535 nm under 980 nm excitation. The luminescence lifetime for 4I13/2 of Er3+ ions is 7.85 ms. The emission cross section at 1535 nm was calculated to be 7.11 × 10−21 cm2 by using the McCumber theory.

Enhancement of 1.8 μm emission in Er3+/Tm3+ co-doped tellurite glasses: Role of energy transfer and dual wavelength pumping schemes

Thulium (Tm3+) and erbium (Er3+)-doped tellurite glasses were synthesized and explored their spectroscopic properties for optical amplification and medical appliances. The emission at 1.8 μm of Tm3+ ions has been enhanced significantly in Er3+/Tm3+ co-doped tellurite glasses under dual pumping lasers at 808 and 980 nm. Emission cross-section of the Tm3+ ions is found to be 3.46 × 10−20 cm2 which was evaluated by utilizing the Mc-Cumber theory. The possible energy transfer mechanisms between Er3+ and Tm3+ ions under 808 and 980 nm excitations were investigated by utilizing the excitation, emission and decay curve analyses. Effect of dual wavelength pumping on the 1.5 and 1.8 μm spectral profiles is also enlightened. Decay curves of Tm3+:3H4 → 3F4 (1440 nm) transition and Er3+: 4I13/2 → 4I15/2 (1531 nm) transition in the Tm3+ singly and Er3+/Tm3+ co-doped tellurite glasses have been analyzed under 808 nm laser excitation. Energy transfer efficiency is evaluated between Er3+: 4I13/2 and Tm3+:3F4 states from the decay curves and it is found to be 83%. The results are significant and indicating that the Er3+/Tm3+ co-doped tellurite glasses could be a potential candidate for optical fiber amplification at around 1.8 μm region under dual wavelength pumping scheme.

Effect of Bi2O3 on JO parameters and spectroscopic properties of Er3+ incorporated sodiumfluoroborate glasses for amplifier applications

This work delivers effect of bismuth on the luminescence and gain characteristics of Er3+ ions incorporated sodiumfluoroborate glasses prepared through melt quenching method. Employing the absorption spectral measurements, Judd–Ofelt intensity parameters (Ω2,Ω4,Ω6) were determined and are used to compute various luminescence radiative properties. From visible emission profile studies, stimulated emission cross-section, CIE color coordinate and Color Correlated Temperature values pertaining to the titled glasses are evaluated. Using Mc-Cumber theory, absorption cross-section (σa), emission cross-section (σe), gain coefficient values for NIR 4I13/2→4I15/2 transition are evaluated and compared with other reported glasses. Of all the present glasses, 40BiBNCE glass exhibit higher σa (66.49 × 10–22 cm2), σe (75.95 × 10–22 cm2) and optimum value of figure of merit (402.54 × 10−28 cm3). Based on the visible and NIR luminescence features, 40BiBNCE glass can be suggested as a potential candidate for the fabrication of solid state lasers, gain medium for 1.53 µm optical amplifier applications.

Thermal, structural, mechanical and 1.8 μm luminescence properties of the thulium doped Pb-K-Al-Na glasses for optical fiber amplifiers

ABSTRACT Lead based phosphate glasses with the concentration variation of Tm3+ ions (PPbKANTm) were prepared by using melt-cast technique. These glasses are characterized by using thermal (DSC), structural (XRD and Raman), mechanical (Knoop hardness) and optical (absorption, emission and lifetime) studies. The structural geometry of the PPbKAN glasses were explored by Raman spectrum and the phonon energy was found to be 1124 cm−1. The three Judd-Ofelt parameters were obtained in order to attain information about the ligand environment, radiative lifetime as well as branching ratios of Tm3+ ion. In general, McCumber theory found to be quite successful to evaluate the cross-section of the metastable state, 3F4→3H6 (1.8 μm). Distinctive down-conversion (420–500 nm) was studied by exciting the 1G4(Tm3+) state. The decay rate of 1D2→3F4 level measured for all the concentrations under λexc = 355 nm. With λexc = 808 nm, the near-infrared emission spectra was also studied and the spectra having two emission transitions of 3H4→3F4 at 1.47 μm and 3F4→3H6 around 1.8 μm. The emission intensity increases with increasing Tm3+ ions concentration upto 1.0 mol% and decreases beyond 1.0 mol% where the optimal 1.8 μm emission is observed when Tm3+ ions concentration is 1.0 mol%. From the near-infrared emission spectra, the crucial spectroscopic parameters such as emission (1.41 × 10−20 cm2) cross-section, effective bandwidth (197 nm) and gain coefficient (277.7 × 10−27 cm3) were evaluated. The Knoop hardness was measured for all the glasses and confirms that the present lead based phosphate glasses doped with Tm3+ ions are mechanically stable. From the analysis of the outcome, it was concluded that the present PPbKANTm glasses are useful for broad band amplifications.

Spectroscopic investigations on Yb3+ doped and Pr3+/Yb3+ codoped tellurite glasses for photonic applications

In this work, we report on structural and spectroscopic properties of Yb3+ doped and Pr3+/Yb3+ co-doped TeO2-Bi2O3-ZnO-Li2O-Nb2O5 (TBZLN) tellurite glasses. Bending and stretching modes of TeO2 and Te–OH bond (strong and weak) were analysed from the deconvolution of observed Raman and FT-IR spectra. Based on the absorption measurements, the energy bands of Yb3+ and Pr3+ ions are assigned. The spectroscopic properties for the radiative transitions of Yb3+ and Pr3+ ions were reported using McCumber and Judd-Ofelt theories. Visible emission bands originating from 3P1 and 3P0 to lower lying levels of Pr3+ were registered under 447 nm excitation. The emission band around 1334 nm assigned to the Pr3: 1G4→3H5 was observed when excited at 980 nm. The stimulated emission cross-section (σemi(λ)) and effective linewidth (Δλeff) for the 3P1→3H6, 3P1→3H5, 3P0→3H6, 3P0→3F2, 3P1→3F3, 3P1→3F4, 3P0→3F4 and 1G4→3H5 transitions of Pr3+ are reported. Upconversion luminescence in Pr3+/Yb3+ co-doped glass upon 980 nm excitation was measured. Possible resonant transfer processes between Yb3+ and Pr3+ ions are presented and discussed. The chromaticity co-ordinates were also evaluated from the visible emission spectra showing that Pr3+/Yb3+ co-doped glass may be suitable for the development of yellow-orange (λexc = 447 nm) and near white light (λexc = 980 nm) emitting devices in photonics.

Energy transfer induced enhancement in NIR luminescence characteristics of Yb3+/Er3+ co-doped sodium zinc bismuth fluorophosphate glasses

The results pertaining to the energy transfer-based photoluminescence characteristics of Er3+-doped and Yb3+/Er3+ co-doped NaF–ZnO–BiF3–NH4H2PO4 (NZBFP) glasses prepared through melt-quench technique were demonstrated here. By applying McCumber's theory, the absorption, stimulated emission cross-sections and optical gain have been estimated for Yb3+ (0.97 μm) and Er3+ (1.54 μm) ions. Yb3+-doped glass exhibited a sharp emission at 979 nm at 808 nm excitation while Er3+-doped glass displayed a broad NIR emission band at/around 1545 nm for 980 nm excitation. The presence of Yb3+ absorption band along with the Er3+ absorption bands in the co-doped glass suggests the energy transfer (ET) possibility within these ions. On pumping Er3+-doped &yYb3+/Er3+ co-doped NZBFP glasses with 980 nm Laser Diode, a broad Er3+ emission at 1545 nm attributed to 4I13/2 → 4I15/2 is observed in the NIR region. The increasing of Yb3+concentration with respect to Er3+ (fixed to 1 mol%) in co-doped glasses have resulted in enhancement of Er3+ NIR emission because of the resonant energy transfer (ET) process from Yb3+→Er3+. The energy transfer (ET) mechanism has been illustrated from the spectral overlap of Yb3+ emission and Er3+ absorption, Er3+ decay lifetime curves, and partial energy level diagram. Further, the nature of interaction responsible for the energy transfer process (ET) has been explained using Forster-Dexter theory and I–H fitting. In addition, the suitability of the present synthesized fluorophosphate glasses for optical amplifier and NIR laser applications were explored in terms of optical amplification and gain parameters, like effective band-width (Δλeff), stimulated emission cross-section (σe), optical gain (G), and gain bandwidth (ΔG).