Effect of OH− content on emission properties in Er3+-doped tellurite glasses

A series of tellurite glasses of composition, 75TeO₂–20ZnO–(5 ? x)La₂O₃–xEr₂O₃ (x = 0.05, 0.1, 0.3, 0.6, 1.0, 2.0, and 3.0 mol%) with different hydroxl content were prepared. The effect of Er³⁺ and OH^? groups concentration on the emission properties of Er³⁺: ⁴I_13/2 → ⁴I_15/2 transition in tellurite glasses was investigated. The constant K_OH–Er for Er³⁺ in tellurite glasses, which represents the strength of interaction between Er³⁺ and OH^? groups in the case of energy migration, was about 14 × 10^?19 cm⁴ s^?1. The interaction parameter C_Er,Er for the migration rate of Er³⁺: ⁴I_13/2 → ⁴I_13/2 transition in tellurite glass was 46 × 10^?40 cm², which indicates that concentration quenching in Er³⁺-doped modified tellurite glass for a given Er³⁺ concentration is much stronger than in silicate and phosphate glasses.     

Optical properties of Er3+-singly doped and Er3+/Yb3+-codoped novel oxyfluoride glasses

Novel oxyfluoride glasses SiO₂–Al₂O₃–Na₂O–ZnF₂ doped with Er³⁺ and Er³⁺/Yb³⁺ were fabricated. The optical properties of the synthesized glasses were experimentally and theoretically investigated in detail. The experimental and calculated oscillator strengths of Er³⁺ were determined by measurement of the absorption spectrum of Er³⁺-singly doped glass. According to the Judd–Ofelt theory, the experimental intensity parameters were calculated, from which the radiative transition probabilities, fluorescence branching ratios and radiative lifetimes were obtained. The fluorescence lifetime and quantum efficiency for the near-infrared emission of Er³⁺-singly doped glass were determined to be 3.0 ms, and 42%, respectively. Visible upconversion luminescence was observed under 980 nm diode laser excitation. The dependence of the upconversion emission intensity upon the excitation power was examined, and the upconversion mechanisms are discussed.     

Recent photoluminescence research on chalcogenide glasses for photonics applications

The optical properties of GeGaSe glasses doped with Er by the addition of Er₂S₃ have been investigated. Optically uniform glasses have been prepared using stoichiometric compositions with 9–12 at.% Ga and doped with 0.5–2 at.% Er. The radiative lifetime of the ⁴I_13/2 → ⁴I_15/2 transition has been estimated to be equal to 1.78 ms using the Judd–Ofelt analysis. The photoluminescence lifetime distribution has been investigated in optimized glasses using Quadrature Frequency-Resolved Spectroscopy at room and liquid helium temperatures and at different emission wavelengths. All lifetime distributions were found to be sharp peaks centered at ∼2 ms. A radiation diffusion model has been used to understand the discrepancy between measured photoluminescence spectra and those predicted by the McCumber theory. The model predicts a radiative lifetime of the ⁴I_13/2 → ⁴I_15/2 transition to be around 1.72 ms and a much longer non-radiative lifetime. These results assume quasi-uniform distribution of Er³⁺ ions with negligible concentration-self-quenching and negligible rate of non-radiative relaxation from ⁴I_13/2 to ⁴I_15/2.     

Spectroscopic and lasing properties of Er3+-doped glass microspheres

We report experimental results on the characterization of microspherical cavities fabricated in Er³⁺-doped modified-silica and phosphate glasses. The spectroscopic properties of the bulk precursor glasses as compared to the obtained microspheres were investigated by photoluminescence spectroscopy and lifetime measurement for the ⁴I_13/2 → ⁴I_15/2 transition of Er³⁺ ions. In both types of glasses we demonstrate whispering gallery mode laser action at various wavelengths around 1550 nm by using a 1480 nm pump laser coupled through a tapered fiber.     

Optical spectroscopy and local structure of Er3+ luminescence centres in СaO–Ga2O3–GeO2 glasses

Optical absorption, luminescence excitation and emission spectra of Er³⁺ centres in Ca₃Ga₂Ge₃O₁₂:Er glass with Er content of 1.46 wt% are presented and analysed. Luminescence kinetics for the main Er³⁺ transitions was satisfactorily described by single exponential decays with characteristic lifetimes. Oscillator strengths, phenomenological Judd–Ofelt intensity parameters, radiative decay rates (emission probabilities of transitions), branching ratios and radiative lifetimes for Er³⁺ centres in Ca₃Ga₂Ge₃O₁₂:Er glass are calculated and compared with the corresponding parameters of the Ca₃Sc₂Ge₃O₁₂:Er³⁺ garnet and other crystals and glasses. Quantum efficiency, η, of the ⁴I_13/2 → ⁴I_15/2 Er³⁺ transition is determined. Incorporation peculiarities and local structure of Er³⁺ luminescence centres in Ca₃Ga₂Ge₃O₁₂:Er³⁺ glass are discussed in comparison with garnet crystals and oxide glasses. On the basis of the presented results and referenced EXAFS data for Er, Eu and Ho impurities (L₃-edge) it has been shown that Er³⁺ centres in Ca₃Ga₂Ge₃O₁₂ glass occupy network sites with the coordination number to oxygen of N = 6.     

Broadband near-infrared emission from Bi–Er–Tm Co-doped germanate glasses

Bi–Er–Tm co-doped germanate glasses and Bi, Er, Tm singly doped glasses were prepared and characterized through absorption spectra, NIR emission spectra and decay lifetime. A super broadband near-infrared emission from 1000 nm to 1600 nm, covering the whole O, E, S, C, and L bands, was observed in the Bi–Er–Tm co-doped samples due to the result of the overlapping of the Bi related emission band (centered at 1300 nm), the emission from Er^{3+ 4}I_13/2 → ⁴I_15/2 transition (centered at 1534 nm) as well as the emission from Tm^{3+ 3}H₄ → ³F₄ transition (centered at 1440 nm), which is essential for broadly tunable laser sources and broadband optical amplifiers. The energy transfer process was also discussed at the end of the paper.     

Laser transition characteristics of Nd3+-doped fluorophosphate laser glasses

Fluorophosphate glasses of composition P₂O₅–K₂O–MgO–Al₂O₃–AlF₃ and P₂O₅–K₂O–MgO–Al₂O₃–BaF₂ were prepared with different Nd³⁺ ion concentrations. The absorption and emission spectra in the UV–VIS–NIR region were measured for these glasses. Judd–Ofelt analysis has been carried out using the absorption spectra of 1.0 mol% Nd³⁺-doped glasses to evaluate the radiative properties for some luminescent levels of the Nd³⁺ ion. The stimulated emission cross-sections of the ⁴F_3/2 → ⁴I_11/2 laser transition for the present glasses are found to be higher than for other Nd³⁺-doped glasses. Branching ratio calculations also revealed the potentiality of the ⁴F_3/2 → ⁴I_11/2 transition for laser action in these glasses. The observed concentration quenching of the lifetime of the ⁴F_3/2 level is explained as a result of cross-relaxation process between the Nd³⁺ ions.     

2 μm spectroscopic investigation of Tm3+-doped tellurite glass fiber

TmF₃ doped TeO₂–ZnO–La₂O₃ (TZL) glasses and fibers have been prepared by the conventional melt-quenching and suction casting methods, respectively. 2 μm emission properties and energy transfer mechanisms of the TZL glasses and fibers have been analyzed and discussed. The oscillator strength, Judd–Ofelt parameters, radiative transition probability and radiative lifetime of Tm³⁺ have been calculated based on the absorption spectra and Judd–Ofelt theory. The maximum emission cross-section of Tm³⁺ is 6.9 × 10^?21 cm² near 2 μm. Emission spectra have been obtained from both TZL fibers and bulk glass when excited with a 794 nm pump. The results of 2 μm emission spectra indicate that the line width of Tm³⁺ measured in fibers is narrower than that in the bulk glass sample. The peak position of the emission spectra shifts to longer wavelength with increment of the fiber length.     

Efficient plasmonic coupling between Er3 +:(Ag/Au) in tellurite glasses

We report a systematic study of the localized surface plasmon resonance effects on the photoluminescence of Er^3 +-doped tellurite glasses containing Silver or Gold nanoparticles. The Silver and Gold nanoparticles are obtained by means of reduction of Ag ions (Ag⁺ → Ag⁰) or Au ions (Au^3 + → Au⁰) during the melting process followed by the formation of nanoparticles by heat treatment of the glasses. Absorption and photoluminescence spectra reveal particular features of the interaction between the metallic nanoparticles and Er^3 + ions. The photoluminescence enhancement observed is due to dipole coupling of Silver nanoparticles with the ⁴I_13/2 → ⁴I_15/2 Er^3 + transition and Gold nanoparticles with the ²H_11/2 → ⁴I_13/2 (805 nm) and ⁴S_3/2 → ⁴I_13/2 (840 nm) Er^3 + transitions. Such process is achieved via an efficient coupling yielding an energy transfer from the nanoparticles to the Er^3 + ions, which is confirmed from the theoretical spectra calculated through the decay rate.     

Fabrication and characterization of Er3+-doped GeO2–PbO and GeO2–PbO–Bi2O3 glass fibers

Glass fibers were drawn from GeO₂–PbO–Bi₂O₃ and GeO₂–PbO melts previously doped with Er³⁺. From the differential thermal analysis curve, the glass transition temperature was determined to be 420 °C, and no crystallization peak was observed in the temperature range of that analysis, indicating stability with regard to devitrification. Raman spectroscopy was performed to characterize the structure of the glasses, which exhibited large transmission windows (0.5–5.0 μm) and large refractive indices (∼2.0). Infrared to visible upconversion of Er³⁺ was observed in the fibers. The visible emissions were related to the upconverted green emissions at about 530 nm (²H_11/2 → ⁴I_15/2) and 550 nm (⁴S_3/2 → ⁴I_15/2), and red emission at 668 nm (⁴F_9/2 → ⁴I_15/2) under 980 nm excitation. The infrared transition (⁴I_13/2 → ⁴I_15/2) was peaked at 1.53 μm. The results obtained suggest that the fibers exhibit the same structures as the parent glasses and can be used in upconversion fiber optical devices.     

Photoluminescence lifetime spectrum in erbium doped Ge–Ga–S glasses

Ge₃₀Ga₄S_65.5:Er_0.5 glasses with stoichiometric composition have been prepared using a conventional melt-quenching technique. The PL lifetime distribution corresponding to ⁴I_13/2 → ⁴I_15/2 transition in Er³⁺ ion has been measured experimentally using quadrature frequency-resolved PL spectroscopy (QFRS) from 2 ns to 160 s at room temperature and at 3.7 K. The distribution seems to be principally single-peaked at around τ_QFRS ≈ 3–4 ms with a half width <3 ms irrespective of PL energy and temperature. The Judd–Ofelt analysis based on optical transitions from ⁴I_15/2 level to ⁴I_13/2, ⁴I_11/2, ⁴I_9/2, ⁴F_9/2, ⁴S_3/2, ²H_11/2 and ⁴F_7/2 levels in Er³⁺ ions gives the radiative lifetime of ⁴I_13/2 → ⁴I_15/2 transition τ_JO ≈ 2.6 ms. The closeness of τ_JO and τ_QFRS implies the dominant role of the radiative relaxation in ⁴I_13/2 → ⁴I_15/2 transitions. The shape of steady-state PL spectra can be predicted by using a modified McCumber theory taking into account the possibility of absorption and re-emission of PL quanta in heavily doped materials under weak excitation. The latter calculations used Monte Carlo simulations taking into account the re-absorption and re-emission of the PL radiation. The non-radiative lifetime for the ⁴I_13/2 → ⁴I_15/2 transition has been estimated to be more than 100 times larger than the radiative lifetime.     

Judd–Ofelt analysis of Nd3+ ions in poly(styrene sulfonate) films

In this work, we present the synthetic route and the optical characterization of poly(styrene sulfonate) (PSS) films doped with Neodymium ions (Nd³⁺). In the synthesis optimization we obtained the maximum incorporation of Nd³⁺ in the matrix about 14.0%. The UV–Vis–NIR curve presents an intense characteristic electronic transition ⁴I_9/2 → ⁴F_5/2 + ²H_9/2 at 800 nm. It was also shown the radiative transition ⁴F_3/2 → ⁴I_11/2 at about 1060 nm. Judd–Ofelt theory was used in order to obtain the near infrared Nd³⁺ radiative transition rate, emission cross-section and radiative lifetime.     

1.5 μm Emission and infrared-to-visible frequency upconversion in Er+3/Yb+3-doped phosphoniobate glasses

Sodium phosphoniobate glasses with the composition (mol%) 75NaPO₃–25Nb₂O₅ and containing 2 mol% Yb³⁺ and x mol% Er³⁺ (0.01 ⩽ x ⩽ 2) were prepared using the conventional melting/casting process. Er³⁺ emission at 1.5 μm and infrared-to-visible upconversion emission, upon excitation at 976 nm, are evaluated as a function of the Er³⁺ concentration. For the lowest Er³⁺ content, 1.5 μm emission quantum efficiency was 90%. Increasing the Er³⁺ concentration up to 2 mol%, the emission quantum efficiency was observed to decrease to 37% due to concentration quenching. The green and red upconversion emission intensity ratio was studied as a function of Yb³⁺ co-doping and the Er³⁺–Er³⁺ energy transfer processes.     

The study of Sm3+-doped low-phonon-energy chalcohalide glasses

The Sm³⁺-doped low-phonon-energy (LPE) Ge–Ga–Se–CsI glasses were studied. Upon excitation at 980 nm diode laser, intense 1.25 and 1.49 μm near-infrared fluorescence bands with broad full width at half maximum (FWHM) of 49 and 53 nm were observed, respectively. About 180–300 μs fluorescence lifetimes were obtained for the 1.49 μm emission. The thermal properties and structure of glasses were investigated by differential thermal analysis (DTA) and Raman spectra, respectively. Spectroscopic characteristics of the optical transitions have been calculated by using the Judd–Ofelt theory and evaluated for excited levels.     

Effect of the ytterbium concentration on the upconversion luminescence of Yb3+/Er3+ co-doped PbO–GeO2–Ga2O3 glasses

The effect of Yb³⁺ concentration on the frequency upconversion (UPC) of Er³⁺ in PbO–GeO₂–Ga₂O₃ glasses is reported for the first time. Samples were prepared with 0.5 wt% of Er₂O₃ and different concentrations of Yb₂O₃ (1.0–5.0 wt%). The green (523 and 545 nm) and red (657 nm) emissions are observed under 980 nm diode laser excitation. The dependence of the frequency UPC emission intensity upon the excitation power was examined and the UPC mechanisms are discussed. An interesting characteristic of these glasses is the increase of the ratio of red to green emission, through an increase of the Yb³⁺ concentration due to an efficient energy transfer from Yb³⁺ to Er³⁺.     

Spectral studies of Sm3+ and Dy3+ doped lithium cesium mixed alkali borate glasses

The effect of host glass composition on the optical absorption and fluorescence spectra of Sm³⁺ and Dy³⁺ has been studied in mixed alkali borate glasses of the type 67B₂O₃ · xLi₂O · (32 − x)Cs₂O (x = 8, 12, 16, 20 and 24). The Judd–Ofelt intensity parameters (Ω₂, Ω₄ and Ω₆) are calculated. The radiative transition probabilities (A), radiative lifetimes (τ_R), branching ratios (β) and integrated absorption cross-sections (Σ) are computed for certain excited states of Sm³⁺ and Dy³⁺ ions for different x values in the glass matrix. Stimulated emission cross-sections (σ_p) are obtained for certain emission transitions of two ions in these mixed alkali borate glasses. These parameters are compared for different x values in the glass matrix. Variation of these parameters with x in the glass matrix has been studied.     

Thermo-optical properties and nonradiative quantum efficiency of Er3+-doped and Er3+/Tm3+-co-doped tellurite glasses

Thermal lens (TL) measurements were performed in tellurite glasses, 70TeO₂–19WO₃–7Na₂O–4Nb₂O₅ (mol%), undoped, doped with Er³⁺ (1.19 × 10²⁰ ions/cm³) and co-doped with Er³⁺ (1.19 × 10²⁰ ions/cm³)/Tm³⁺ (1.56 × 10²⁰ ions/cm³). The absolute nonradiative quantum efficiency (ϕ) was determined by the TL method. The ϕ values for Er³⁺/Tm³⁺-co-doped and Er³⁺-doped tellurite glasses were 0.98 and 0.74, respectively. Fluorescence spectra were performed at λ_e = 488 nm and used to estimate the fluorescence quantum efficiency (η) using the TL results. These values were compared with results obtained by Judd–Ofelt calculations.     

Low-temperature Er3+ emission in Ge–S–Ga glasses excited by host absorption

The photoluminescence (PL) of a series of (GeS₂)₈₀(Ga₂S₃)₂₀ glasses doped with different amounts of Er (0.17, 0.35, 0.52, 1.05 and 1.39 at.%) at 77 and 4.2 K has been studied. The influence of the temperature on the emission cross-section of the PL bands at ∼1540, 980 and 820 nm under host excitation has been defined. A quenching effect of the host photoluminescence has been established from the compositional dependence of the PL intensity. It has been found that the present Er³⁺-doped Ge–S–Ga glasses posses PL lifetime values about 3.25 ms.     

Spectroscopic properties and energy transfer in Ga2O3– Bi2O3–PbO–GeO2 glasses codoped with Tm3+ and Ho3+

This paper reports on the spectroscopic properties and energy transfer in Ga₂O₃–Bi₂O₃–PbO–GeO₂ glasses doped with Tm³⁺ and/or Ho³⁺. From the optical absorption spectra of Tm³⁺, Judd–Ofelt intensity parameters, radiative transitions probabilities, fluorescence branching ratios, and radiative lifetimes have been calculated using Judd–Ofelt theory. The measured differential scanning calorimetry result shows that the glass exhibits excellent stability against devitrification with ΔT = 129 °C. The measured luminescence spectra show that the ³H₄ → ³F₄ transition of Tm³⁺ upon 808 nm laser diode excitation possess a broad full width at half-maximum of ∼126 nm. The maximum value calculated stimulated emission cross-section and the measured lifetime of ³H₄ level from the 1.47-μm transition are ∼4.73 × 10⁻²¹ cm² and ∼0.239 ms, respectively. It is noticed that codoping of Ho³⁺ could significantly enhanced the ratio of the intensity of 1.47–1.80 μm by energy transfer via Tm³⁺: ³F₄ → Ho³⁺: ⁵I₇.     

Upconversion and concentration quenching in Er3+-doped TeO2–Na2O binary glasses

The spectroscopic properties of Er³⁺-doped alkali tellurite TeO₂–Na₂O glasses are investigated. Infrared-to-visible upconversion emission bands are observed at 410, 525, 550 and 658 nm using 797 nm excitation wavelength. These bands are assigned to the ²H_9/2 → ⁴I_15/2, ²H_11/2 → ⁴I_15/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 transition, respectively. The power dependence study reveals that the ²H_9/2 → ⁴I_15/2 transition involves a three-step process while the other upconversion transitions involve only two steps. An excitation with 532 nm wavelength, two upconversion bands are observed in the UV region at 380 and 404 nm in addition to bands in the visible region at 410, 475, 525, 550, 658 and 843 nm. These bands are ascribed to ⁴G_11/2 → ⁴I_15/2, ²P_3/2 → ⁴I_13/2, ²H_9/2 → ⁴I_15/2, ²P_3/2 → ⁴I_11/2, ²H_11/2 → ⁴I_15/2, ⁴S_3/2 → ⁴I_15/2, ⁴F_9/2 → ⁴I_15/2 and ⁴S_3/2 → ⁴I_13/2 transition, respectively. Increasing Er³⁺ concentration leads to a rapid growth in the intensity of red emission relative to that for the green emission. An explanation for this observation has been suggested. The temperature dependence profile for the two thermally coupled levels (²H_11/2, ⁴S_3/2) shows that they can be used for measuring the temperature.