Optical transitions in Er^3＋ doped lead germanate glasses

Er^{3+}- and Er^{3+}/Yb^{3+}-doped lead germanate glasses that are suitable for use in fibre lasers and optical amplifiers as well as optical waveguide devices have been fabricated and characterized. The absorption spectra from near-infrared to visible were obtained and the Judd－Ofelt parameters were determined from the absorption band. Intense and broad 1.53μm infrared fluorescence and visible upconversion luminescence were observed under 976 nm diode laser excitation. For 1.53μm emission band, the full widths at half-maximum are 36, 37, 51 nm for GPE, GPYE and GPFE samples, respectively. For frequency upconversion emission, the intense bands centred at around 524, 545, 657nm are due to the {}^4S_{3/2}+{}^2H_{11/2}→{}^4I_{15/2} and {}^4F_{9/2}→{}^4I_{15/2} transitions of Er^{3+} ions. The quadratic dependence of the green and red emissions on excitation power indicates that the two-photon absorption process occurs under the 976nm excitation.     

Up-conversion luminescence research of Er（0.5）：ZBLAN material for volumetric display application when excited by 1520nm laser

The up-conversion luminescence of the ZBLAN fluoride glass Er(0.5):ZBLAN, when excited by a 1520 nm semiconductor laser, is studied in this paper. The absorption and common-fluorescence spectra are also measured in order to understand the up-conversion clearly. It is found that there are seven strong up-conversion luminescence lines (406.97^m, 410.42 nm), (521.97^m, 527.56 nm), (542.38^m, 549.27 nm), (654.27^m, 665.70 nm), 801.57^m nm, 819.46 nm, and 840.00 nm, which can be recognized as the fluorescence transitions of ({}^2G^4F^2H)_{9/2}→{}^4I_{15/2},{}^2H_{11/2}→ {}^4I_{15/2},{}^4S_{3/2}→{}^4I_{15/2},{}^4F_{9/2}→{}^4I_{15/2}, {}^4I_{9/2}→ {}^4I_{15/2}, ({}^2G^4F^2H)_{9/2}→{}^4I_{9/2}, and {}^4S_{3/2}→{}^4I_{13/2} respectively. Meanwhile, the small up-conversion fluorescence lines 379.20 nm, 453.10 nm and 490.60 nm are the transitions of {}^4G_{11/2}→{}^4I_{15/2},{}^4F_{5/2}→{}^4I_{15/2} and {}^4F_{7/2}→ {}^4I_{15/2} respectively. It is interesting that the slopes of log F－logP curves, the double-logarithmic variation of up-conversion luminescence intensity F with laser power P, are different from each other for these observed up-conversion luminescence, this being valuable for the volumetric display. Comprehensive discussions find that the {}^4G_{11/2}→{}^4I_{15/2}, (^2G^4F^2H)_{9/2}→{}^4I_{15/2}, (^2H_{11/2}→{}^4I_{15/2},{}^4S_{3/2}→{}^4I_{15/2},{}^4F_{9/2}→ {}^4I_{15/2}), and {}^4I_{9/2}→{}^4I_{15/2} up-conversion luminescences are five-photon, four-photon, three-photon, and two-photon up-conversion luminescences respectively. It is found also that the absorption from ground-state {}^4I_{15/2} level to {}^4I_{13/2} level is very large, which is beneficial to the sequential energy transfer up-conversion to occur.     

Comparative study of spectroscopic properties of Er^3＋／Yb^3＋-codoped tellurite glass and fibres under 980nm excitation＊

A tellurite fibre of TeO_{2}－ZnO－La_{2}O_{3}－Li_{2}O glass codoped with 20000 ppm ytterbium and 5000 ppm erbium was fabricated by the suction casting and rod-in-tube technologies. The absorption spectrum of Er^{3+}/Yb^{3+} -codoped bulk glass has been measured. From the Judd－Ofelt intensity parameters, the spontaneous emission probability and radiative lifetime τ_{rad} of Er^{3+}:{}^{4}I_{13/2}→{}^{4}I_{15/2} transition for the bulk glass have been calculated. The emission fluorescence spectra and lifetimes around 1.5μm, and subsequent upconversion fluorescence in the range of 500－700nm were measured in fibres and compared with those in bulk glass. The changes in amplified spontaneous emission with fibre length and pumping power was also measured. It was found that the emission spectrum from erbium in fibres is almost twice as broad as the corresponding spectrum in bulk glass when pumped at 980nm.     

Blue Upconversion Luminescence in Tm^3＋／Yb^3＋-Codoped Lead Chloride Tellurite Glass

The upconversion properties of Tm^3 /Yb3 -codoped lead chloride tellurite glass under 980hm excitation were investigated. The intense blue (476nm) emission and weak red (649 nm) emission corresponding to the ^1G4→4 ^3H6 and ^1G4→^3H4 transitions of Tm^3 ions, respectively, were simultaneously observed at room temperature. The dependence of upconversion intensities on excitation power and the possible upconversion mechanisms are evaluated. The intense blue upconversion luminescence of Tm^3 /Yb^3 -codoped lead chloride tellurite glass can be used as potential host material for the development of blue upconversion optical devices.     

Frequency Upconversion Emission of Er^3＋-Doped Strontium-Lead-Bismuth Glasses

Er^3 -doped strontium-lead-bismuth glasses for developing potential upconversion lasers have been fabricated and characterized. Under 975 nm excitation, intense green and red emissions centred at 525, 546, and 657nm,corresponding to the transitions ^2H11/2 → ^4I15/2, ^4S3/2 → ^4I15/2, and ^4F9/2 → ^4I15/2, respectively, were observed at room temperature. The upconversion mechanisms are discussed based on the energy matching and quadratic dependence on excitation power, and the dominant mechanisms are excited state absorption and energy transfer upconversion for 525 and 546nm emissions, and energy transfer upconversion for 657nm emission.     

Oscillation conditions of cw simultaneous dual-wavelength Nd：YAG laser for transitions 4F3／2-4I9／2 and 4F3／2-4I11／2

The operating condition of a cw simultaneous dual-wavelength Nd:YAG laser for both {}^4F_{3/2}-{}^4I_{9/2} (quasi-three-level system) and {}^4F_{3/2}-{}^4I_{11/2}(four-level system) transitions is studied. According to this condition, the cw simultaneous dual-wavelength at 1.06μm and 946 nm in Nd:YAG crystal has been realized experimentally through an adaptive coating design of the cavity mirrors. A total power output of 2.5W of the dual-wavelength at 946nm and 1.06μm has been achieved with an optical conversion efficiency 14.3%. The experimental results are in good agreement with the theoretical analysis.     

Host dependent thermal stability and frequency upconversion of Er^3＋-doped heavy metal oxyfluoride germanate glasses

The upconversion properties of Er^3＋-doped heavy metal oxyfluoride germanate glasses under 975 nm excitation have been investigated. The intense green （551 and 529 nm） and relatively weak red （657 nm） emissions corresponding to the transitions ^4S3/2→^4I15/2, ^2H11/2→^4 I15/2 and ^4F9/2 →^4I15/2, respectively, were simultaneously observed at room temperature. The content of PbF2 has an important influence on the upconversion luminescence emission. With increasing content of PbF2, the intensities of green （529 nm） and red （657 nm） emissions increase slightly, while the green emission （551 nm） increases markedly. These results suggest that PbF2 has an influence on the green （551 nm） emission more than on the green （529 nm） and red （657 nm） emissions.     

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.     

High Efficiency Infrared to Visible Upconversion in Er3＋／yb3＋—Doped Lead Halide Tellurite Glass

Strong upconversion luminescence of Er3 /Yb3 -doped lead halide tellurite glass under 976nm excitation is demonstrated. Three emission bands centred at 525 nm, 545 nm, and 655 nm resulting from the transitionsfrom the excited states 2H11/2, 4S3/2, and 4F9/2 to the ground state 4I15/2, respectively, are observed evenat 60mW pumping power. The power dependent intensity and the upconversion mechanisms responsible forthe luminescence are evaluated and discussed. The obtained results might provide useful information for thedevelopments of upconversion lasers.     

UV and visible upconversion luminescence in Er^3＋：YAG under red laser excitation

This paper reports that the ultraviolet and visible upconversion luminescence from the ^4S3/2, ^2G9/2 and ^2P3/2 levels have been observed in Er^3＋：YAG following 647.2 nm excitation of the ^4F9/2 multiple. Upconversion luminescence intensity dependence on pump power was recorded. The measured decay profiles were theoretically fitted by kinetics theory and the basically good agreements were achieved. The results indicate that some energy transfer processes proposed to explain the observed upconversion phenomena are reasonable.     

Laser-diode-excited Blue Upconversion in Tm3+/Yb3+-codoped TeO2-Ga2O3-R2O (R=Li, Na, K) Glasses

This paper reports on intense blue upconversion in Tm³⁺/Yb³⁺ codoped TeO₂-Ga₂O₃-R₂O(R=Li, Na, K) glasses upon excitation with commercial available laser diode (LD). Effects of alkali ions on the Raman spectra, thermal stability and spectroscopic properties of the tellurite-gallium glasses have also been investigated. Energy transfer and the involved upconversion mechanisms have been discussed. Intense blue upconversion emission centered at 476 nm along with a weak red emission at 650 nm has been observed upon excitation of 977 nm LD, assigned to the transitions of , and and/or of Tm³⁺, respectively. The blue upconversion intensity has a cubelike dependence on incident pump laser power, indicating a three-photon process. However, a quadratic dependence of the 476 nm upconversion intensity on the incident pump laser power has been observed when samples under excitation of 808 nm LD due to a two-photon absorption process. Enhanced upconversion luminescence have been observed with replacing K⁺ for Na⁺ and Li⁺.     

Spin polarization effect for Tc2 molecule

Density functional method (DFT) (B3p86) of Gaussian98 has been used to optimize the structure of the Tc_2 molecule. The result shows that the ground state for Tc_2 molecule is an 11-multiple state and its electronic configuration is {}^{11}Σ_g^-, which shows the spin polarization effect of Tc_2 molecule of a transition metal element for the first time. Meanwhile, we have not found any spin pollution because the wavefunction of the ground state does not mingle with wavefunctions of higher energy states. So, that the ground state for Tc_2 molecule is an 11-multiple state is indicative of the spin polarization effect of Tc_2 molecule of a transition metal element: that is, there exist 10 parallel spin electrons. The non-conjugated electron is greatest in number. These electrons occupy different spacious tracks, so that the energy of Tc_2 molecule is minimized. It can be concluded that the effect of parallel spin of the Tc_2 molecule is larger than the effect of the conjugated molecule, which is obviously related to the effect of electron d delocalization. In addition, the Murrell--Sorbie potential functions with the parameters for the ground state {}^{11}Σ_g^- and other states of Tc_2 molecule are derived. Dissociation energy D_e for the ground state of T_{c2} molecule is 2.266eV, equilibrium bond length R_e is 0.2841nm, vibration frequency ω_e is 178.52cm^{-1}. Its force constants f_2, f_3, and f_4 are 0.9200aJ·nm^{-2}, --3.5700aJ·nm^{-3}, 11.2748aJ·nm^{-4} respectively. The other spectroscopic data for the ground state of Tc_2 molecule ω_eχ_e, B_e, α_e are 0.5523cm^{-1}, 0.0426cm^{-1}, 1.6331×10^{-4}cm^{-1} respectively.     

Synthesis and photoluminescence properties of Nd2O3 nanoparticles modified by sodium bis 2-ethylhexyl sulfosuccinate

This paper reports that Nd₂O₃ nanoparticles modified by AOT(sodium bis(2-ethylhexyl) sulfosuccinate) were prepared using microemulsion method in the system of water and propanol/AOT/toluene. Transmission electron microscopy shows that the Nd₂O₃ nanoparticles take the shape of sphere with 18\,nm and 31nm with different preparation. The organic sol of Nd₂O₃ nanoparticles is very stable at room temperature. X-ray diffraction results show that the product has hexagonal phase structure. Two ultraviolet emission band at 344\,nm and 361\,nm corresponding to the transition of ⁴D_3/2→4I_9/2 and 2P_3/2→⁴I₁₁₂ or ⁴D_3/2 →⁴I_13/2 were observed.     

Spectral properties of erbium-doped heavy metal oxyfluoride silicate glasses for broadband amplification

Erbium-doped glasses showing a wide 1.55μm emission band are reported in a novel heavy metal oxyfluoride glass system SiO_2－PbO－PbF_2 and their optical properties such as emission spectra, fluorescence lifetime and the refractive index have been investigated. The broad and flat {}^4I_{13/2}→{}^4I_{15/2} emission of Er^{3+} ions around 1.55μm can be used as host materials for potential optical amplifiers in wavelength-division-multiplexing network system. We find that with increasing PbF_2 content in the glass composition, the fluorescence full width at half maximum and fluorescence lifetime of the {}^4I_{13/2} level of Er^{3+} increase, while refractive index and density decrease.     

A novel yellow emitting phosphor Dy3+, Bi3+ co-doped YVO4 potentially for white light emitting diodes

Novel Y1 x yVO4:xDy3+,yBi3+(0.01 ≤ x ≤ 0.05,0 ≤ y ≤ 0.20) phosphors for light emitting diode(LED) were successfully synthesised by solid-state reaction.The calculation results of electronic structure show that YVO4 has a direct band gap with 3 eV at G.The top of the valence band is dominated by O 2p state and the bottom of the conduction band is mainly composed of O 2p and V 3d states.An efficient yellow emission under near-ultraviolet(365 nm) excitation is observed.Compared with the pure YVO4:Dy3+ samples,the Dy3+,Bi3+ co-doped samples show a more intensive emission peak(at 574 nm) and a new broad emission band(450-770 nm),due to the 4F9/2 6H13/2 transition of Dy3+ and the emission of the VO3 4 Bi3+ complex respectively.The optimum chromaticity index of Y1 x yVO4:xDy3+,yBi3+(0.01 ≤ x ≤ 0.05,0 ≤ y ≤ 0.20) is(0.447,0.497),which indicates that YVO4:Dy3+,Bi3+ has higher colour saturation than the commercial phosphor YAG:Ce3+.The effects of concentration of Dy3+,Bi3+,electric states and the photoluminescence properties are discussed in details.     

The mechanism research of the Cr^4＋Nd^3＋：YAG laser

The 946nm diode-pump microchip self-Q-switched laser of a chromium and neodymium codoped yttrium aluminum garnet crystal material (Cr^{4+}Nd^{3+}:YAG) is studied, especially about its physical mechanism of operation. The {}^4F_{3/2}→{}^4I_{9/2} transition of Nd^{3+} ion is beneficial to achieving laser oscillation in a quasi-three-level system based on coating the cavity mirrors of the microchip with films that suppress the 1064nm operation and enhance the 946nm laser. The Cr^{4+} ion is a saturable absorber. The initial loss N_{t1} is high, which acts as the threshold for laser oscillation. The stable loss N_{t2} is low because the Cr^{4+} ion is acceleratively bleached by the fast enhancement of the oscillating laser. The high N_{t1}, small N_{t2} and fast progresses permit the oscillating laser of the Cr^{4+}Nd^{3+}:YAG to have a good self-Q-switched property whose full width at half maximum is about 4.2ns. Its highest laser power is about 5.7mW. Its peak power is about 150W. Its good fundamental transverse TEM_{00} mode results from the absorption bleaching established by both the pump and oscillating lasers, which suppress other transverse mode and allow the oscillation only in the fundamental transverse TEM_{00} mode.