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.     

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.     

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.     

Absorption and emission of Ho3+ in germanate glasses

Absorption spectra of Ho³⁺ in germanate glasses were measured in the range 300–2500 nm and the intensity parameters were calculated by the Judd-Ofelt theory. Excitation and emission spectra were measured in the visible at a temperature range of 80–573 K. The radiative transition probabilities from the excited states [⁵F₄, ⁵S₂], ⁵F₅, ⁵I₄, ⁵I₅ and ⁵I₆, branching ratios and integrated emission cross-sections were calculated. The non-radiative relaxation rate from the (⁵F₄, ⁵S₂) levels is estimated to be about 2 × 10⁵ s^?1.     

Multiple sites for Er3+ in alkali silicate glasses (II). Evidence of four sites for Er3+

The low-temperature absorption spectrum of a series of binary alkali silicate glasses doped with Er³⁺ shows the presence of four different sites for the Er³⁺. The near-octahedral A site reported in Part I of this series is the principal site and is present in all these glasses. The B site appears in the binary lithium and sodium silicate glasses. The binary potassium, rubidium and cesium glasses show the presence of the C and D sites. The C site absorption spectrum is similar to that found by Gruber et al. for Er³⁺ in Er₂O₃. The D site is probably a variation of the B site. Tentative sixfold-coordinated models are suggested for the B and D sites.     

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.     

Energy transfer between Tm3+ and Er3+ in borate and phosphate glasses

A study of the energy transfer process between thulium and erbium is presented. From our measurements of fluorescence emissions and decay times the energy transfer efficiencies and probabilities were calculated. In this work the energy transfer which occurs between the upper levels in the UV and VIS regions of the two ions was especially studied. In the Tm-Er system, a mutual migration of energy occurs. The energy transfer from thulium to erbium is a multichannel process in which the energy is transferred from all the metastable levels of thulium to the matching energy levels of erbium. In addition, backtransfer of energy from erbium to thulium occurs by crossrelaxation of respective erbium transitions. The efficiency of energy transfer from thulium to erbium is independent of the levels between which the transfer occurs, but is dependent on the matrix. It is concluded that the energy is transferred via the phonons of the host glass.     

Aging,glass transition,supercooled and equilibrium liquid states of alkali germanate glasses studied by Brillouin scattering

The elastic properties of alkali germanate glasses, xR₂O?(100 ? x)GeO₂ (R = Li, Na, K, Rb, Cs ; x = 14, 28), have been studied by Brillouin scattering in the wide temperature range up to 1200 °C. The remarkable aging effect of Brillouin shift Δν_L has been observed below a glass transition temperature T_g ≈ 500 °C. The temperature dependence of longitudinal sound velocity V_L of well annealed glasses shows the gradual decrease below T_g, while on further heating the remarkable decrease is observed above T_g. The scaled temperature dependence of V_L is nearly independent on alkali metals below the melting temperature T_m. While on further heating above T_m, the drastic decrease of V_L and increase of α_L show the remarkable alkali dependence. It may be attributed to the appearance of dynamic process related to ionic hopping of alkali metals released from glass network above T_m.     

Optical properties of Er3+-doped alkali fluorophosphate glasses

A systematic study of the optical absorption and luminescence spectra of Er³⁺-doped alkali fluorophosphate glasses (RTFP) 50(NaPO₃)–10TeO₂–20AlF₃–19RF–1Er₂O₃ (R = Li, Na and K) has been performed. The phenomenological Judd–Ofelt intensity parameters have been determined from the spectral intensities of the absorption bands in order to calculate the radiative transition probabilities, radiative lifetimes and branching ratios for various excited luminescent states. Using the visible and near infrared emission spectra, full width at half maximum (FWHM), emission cross-sections (σ_e) and figure of merit (FOM) were evaluated and compared with other hosts. Especially, the numerical values of these parameters indicate that the emission transition ⁴I_13/2 → ⁴I_15/2 transition at 1.534 μm in Er³⁺-doped fluorophosphate glasses may be highly useful in optical communication. The decay characteristic of ⁴S_3/2 excited level has also been recorded and analyzed. The calculated and experimental lifetimes were compared in terms of quantum efficiencies and multiphonon relaxation rates.     

Manifestation of thermodynamic glass transition by structure and picosecond dynamics in alkali tellurite glasses

The Raman spectra of the 0.1Cs₂O–0.9TeO₂ melt were measured and analyzed over a broad temperature range including the glassy, supercooled and molten state in an effort to follow the varying structural and dynamical aspects caused by temperature and alkali modifier. The network structure of the glass/melt is formed by mixing TeO₄ trigonal bipyramid and TeO₃ trigonal pyramid units. Changing alkali content and/or temperature results to conversion of the TeO₄ units to TeO₃ units with a varying number of non-bridging oxygen atoms. The low-frequency Raman spectra reveal a well-resolved Boson peak whose frequency also depends on temperature. The variation of the maximum of the Boson peak has been determined and discussed in the framework of current phenomenological models. The short-time dynamics of the system experiences drastic changes when approaching the glass-to-liquid transition. The temperature dependent plot of the correlation times extrapolates to a crossover value, which we assign as spectral evidence of the system's known thermodynamic glass transition temperature. Similar behavior exhibit several spectral features, such as the maximum of the Boson peak, the exponent of the susceptibility and the intensity ratio related to the structural transformation from TeO₄ tbp to TeO₃ tp species occurring in the medium range order structure.     

Up-conversion enhancement in Er3 +-Ag co-doped zinc tellurite glass: Effect of heat treatment

The melt quenching method was used to synthesize the Ag⁰ nanoparticles and Er^3 + ions co-doped zinc tellurite glass. The glasses were characterized by differential thermal analyzer, UV–VIS-IR absorption, photoluminescence spectroscopy and TEM imaging. Heat treatment at different annealing time intervals above the glass transition temperature was applied to reduce the Ag⁺ ions to Ag⁰ NPs. The influence of heat treatment on structural and optical properties is examined. Intense and broad up-conversion emissions of silver are recorded in the visible region. Up-conversion luminescence spectra revealed three major emission peaks at 520, 550 and 650 nm originating from ²H_11/2, ⁴S_3/2 and ⁴F_9/2 levels, respectively. An efficient enhancement in visible region is observed for samples containing silver NPs. The absorption plasmon peaks are evidenced around 560 and 594 nm. The effect of localized surface plasmon resonance and the energy transfer from the surface of silver NP to trivalent erbium ions are described as the sources of enhancement.     

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.     

Glass composition dependence of luminescence due to Ge2+ center in germanate glasses

Germanate glasses were prepared by the melt-quenching method using an assembled hot-thermocoupler equipped in a sample chamber of a fluorescence spectrometer, and subsequently their luminescence and excitation spectra were measured. In the GeO₂ glass, luminescence bands due to the Ge²⁺ center appeared at the central wavelengths of 300 and 395 nm, their excitation bands being at 250 and 330 nm, respectively. In the (100 − x)GeO₂ − xM_mO_n glasses, for M_mO_n = B₂O₃ (x ≦ 50), SiO₂ (x ≦ 40), and Al₂O₃ (x ≦ 2), the luminescence intensity and therefore the amount of the Ge²⁺ center increased with increasing the content of M_mO_n, where M^(2n/m)+ ions (B³⁺, Si⁴⁺, and Al³⁺) have lower basicities than a Ge⁴⁺ ion. Contrarily, for M_mO_n = Li₂O (x ≦ 30), Na₂O (x ≦ 20), K₂O (x ≦ 20), CaO (x ≦ 20), SrO (x ≦ 3), BaO (x ≦ 15), ZnO (x ≦ 20), Ga₂O₃ (x ≦ 10), Sb₂O₃ (x ≦ 20), Bi₂O₃ (15 ≦ x ≦ 25), TiO₂ (x ≦ 3), and Nb₂O₅ (x ≦ 10), the luminescence intensity and the amount of the Ge²⁺ center rapidly decreased with increasing the amount of additives and disappeared, where M^(2n/m)+ ions (Li⁺, Na⁺, K⁺, Ca²⁺, Sr²⁺, Ba²⁺, Zn²⁺, Ga³⁺, Sb³⁺, Bi³⁺, Ti⁴⁺, and Nb⁵⁺) have higher basicities than a Ge⁴⁺ ion.     

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.     

Characterization of B2O3 and/or WO3 containing tellurite glasses

Characterization of B₂O₃ and/or WO₃ containing tellurite glasses was realized in the 0.80TeO₂–(0.20 ? x)WO₃ ? xB₂O₃ system (0 ≤ x ≤ 0.20 in molar ratio) by using differential scanning calorimetry, Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectrometry techniques. Glasses were prepared with a conventional melt-quenching technique at 750 °C. To recognize the thermal behavior of the glasses, glass transition and crystallization temperatures, glass stability value, glass transition activation energy, fragility parameter were calculated from the thermal analyses. Density, molar volume, oxygen molar volume and oxygen packing density values were determined to investigate the physical properties of glasses. Fourier transform infrared spectra were interpreted in terms of the structural transformations on the glass network, according to the changing B₂O₃ and/or WO₃ content. Crystallization behavior of the glasses was investigated by in situ X-ray diffraction measurements and microstructural characterization was realized by scanning electron microscopy and energy dispersive X-ray spectrometry analyses.     

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.     

铒镱双掺的钒酸钇和铌酸锂晶体中的铒离子的上转换发光

利用J-O理论,计算了在铒、镱双掺的钒酸钇和铌酸锂晶体中的铒离子在室温下的晶场唯象参数Ωλ(λ=2,4,6)及辐射跃迁几率、无辐射跃迁几率和共振跃迁几率.考虑到铒、镱间的能量转移,写出了在这些晶体中的铒离子的速率方程.速率方程的解表明,在铒、镱双掺的钒酸钇晶体中的铒离子的550 nm的上转换发光,比它在铒、镱双掺的铌酸锂晶体中更为有效.这一理论结果与我们的实验观察结果一致.     

Optical properties of Tm3+ ions in alkali germanate glass

Tm-doped alkali germanate glass is investigated for use as a laser material. Spectroscopic investigations of bulk Tm-doped germanate glass are reported for the absorption, emission and luminescence decay. Tm:germanate shows promise as a fiber laser when pumped with 0.792 μm diodes because of low phonon energies. Spectroscopic analysis indicates low non-radiative quenching and pulsed laser performance studies confirm this prediction by showing a quantum efficiency of 1.69.     

Judd Ofelt calculation of quantum efficiencies and branching ratios of Nd3+ doped glasses

This paper presents the optical characterization of Nd³⁺ lead silicate glasses (SiO₂–Na₂CO₃–PbO–ZnO), synthesized by means of the fusion method. Absorption, luminescence, lifetime and Raman spectroscopy measurements were performed in order to determine the radiative properties of the glasses. The near infrared luminescence exhibited the typical Nd³⁺ bands, particularly the band at 1060 nm (⁴F_3/2 → ⁴I_11/2). The calculated branching ratios for the ⁴F_3/2 level are: β (9/2) = 35%, β (11/2) = 55%, β(13/2) = 9.5% and β (15/2) = 0.5%. The estimated quantum efficiency was about 90%, based on comparison with the Judd Ofelt theory and experimental lifetime measurements.