Investigation on Tm3+-doped silicate glass for 1.8 μm emission

A Tm³⁺-doped silicate glass (SiO₂–CaO–Na₂O–K₂O) with good thermal stability is prepared by the melt-quenching method. Intense 1.8 μm emission is obtained when pumped by an 808 nm laser diode. Based on the measured absorption spectra, radiative properties are predicted using Judd–Ofelt theory and Judd–Ofelt parameters Ω_λ (λ=2, 4, 6), as well as absorption and emission cross-sections are calculated and analyzed. The difference between the measured Tm³⁺:³F₄ lifetime and the calculated lifetime is also discussed. The emission property together with good thermal property indicates that Tm³⁺-doped silicate glass is a potential kind of laser glass for efficient 2 μm laser.     

2.7 μm fluorescence radiative dynamics and energy transfer between Er3+ and Tm3+ ions in fluoride glass under 800 nm and 980 nm excitation

A detailed study of the fluorescence radiative dynamics and energy transfer processes between Er and Tm ions in the Er³⁺/Tm³⁺ doped fluoride glass is reported. The fluorescence properties of 2.7 μm emission, other infrared and visible emissions are investigated under different selective laser excitations. Three Judd–Ofelt intensity parameters, energy transfer microparameters and efficiency have been determined and discussed. It is found that present Er³⁺/Tm³⁺ doped fluoride glass possesses large calculated emission cross section (8.98×10^–21 cm²) around 2.7 μm. The more suitable pumping scheme for laser applications at 2.7 μm laser is 980 nm excitation for Er³⁺/Tm³⁺ doped fluoride glass.     

Broadband 2.84 μm luminescence properties and Judd–Ofelt analysis in Dy3+ doped ZrF4–BaF2–LaF3–AlF3–YF3 glass

2.84 μm luminescence with a bandwidth of 213 nm is obtained in Dy³⁺ doped (ZrF₄–BaF₂–LaF₃–AlF₃–YF₃) ZBLAY glass. Three intensity parameters and radiative properties have been determined from the absorption spectrum based on the Judd–Ofelt theory. The 2.84 μm emission characteristics and energy transfer mechanism upon excitation of a conventional 808 nm laser diode are investigated. The prepared Dy³⁺ doped ZBLAY glass possessing high predicted spontaneous transition probability (45.92 s^?1) along with large calculated emission cross section (1.17×10^?20 cm²) has potential applications in 2.8 μm laser.     

Positive influence of Tm3+ on effective Er3+: 3 μm emission in fluoride glass under 980 nm excitation

Er³⁺ and Tm³⁺ singly doped and codoped new fluoride glasses were prepared by traditional melt-quenching method. Efficient 3 μm emission was obtained under 980 nm laser excitation. It is worthy to notice that one of the two ions can be the sensitizer to the other one by depressing the Er³⁺: 1.5 μm emission through the energy transfer process from Er³⁺:⁴I_13/2 level to Tm³⁺:³F₄ level. On the basis of measured absorption spectra, the Judd-Ofelt intensity parameters and radiation emission probability were calculated to evaluate the spectroscopic properties. Additionally, the micro-parameters together with the phonon assistance of Er³⁺:⁴I_13/2 → Tm³⁺:³F₄ and Er³⁺:⁴I_11/2 → Tm³⁺:³H₅ processes were quantitatively analyzed by using Dexter model. The theoretical micro-parameters results meet well with the experiments which indicates that Er³⁺/Tm³⁺ codoped fluoride glass is a potential kind laser glass for 3 μm laser.     

2μm emission performance in Ho3+ doped fluorophosphate glasses sensitized with Er3+ and Tm3+ under 800 nm excitation

The spectroscopic properties and energy transfer mechanisms in Ho³⁺ doped fluorophosphate glasses sensitized by Er³⁺ and Tm³⁺ at the 2 μm region are investigated. The absorption spectra and fluorescence spectra of the Tm–Ho doubly-doped glass system and Er–Tm–Ho triply-doped glass system are measured. According to the absorption spectra, the Judd–Ofelt parameters and spontaneous transition probability are calculated and compared with those of other glass hosts. From the fluorescence spectra, the fluorescence intensity of Er–Tm–Ho glass system at 2.0 μm is 0.95 and larger than that of the Tm–Ho glass system, which is 0.69. Meanwhile, the 2.0 μm to 1.8 μm and 2.0 μm to 1.53 μm peak intensity ratios in the Er–Tm–Ho glass system are 8.63 and 22.79, respectively, suggesting sufficient energy transfer between Er³⁺, Tm³⁺ and Ho³⁺ ions. In addition, the pumping schemes and energy transfer mechanisms of Tm–Ho doubly-doped and Er–Tm–Ho triply-doped glasses are discussed. The study indicates that the Er–Tm–Ho triply-doped glass system is a significant sensitized way pumped at 800 nm in fluorophosphate glasses for 2 μm applications.     

Mid-infrared photo-luminescence and energy transfer around 2.8 μm from Dy3+/Tm3+ co-doped tellurite glass

Tellurite glasses co-doped with Dy³⁺ and Dy³⁺/Tm³⁺ have been synthesized. Emission around 2.8 μm is successfully obtained in present glass upon excitation of a conventional 808 nm laser diode. Judd-Ofelt intensity parameters and radiative properties of Dy³⁺ ions are calculated using the Judd-Ofelt theory. The luminescence characteristics and energy transfer mechanism are investigated and discussed. According to the absorption, fluorescence spectra and lifetime measurements, Tm³⁺ ions can effectively absorb excitation and transfer their energy to Dy³⁺ ions with high efficiency (up to 86.80%). Hence, the results demonstrate that Dy³⁺/Tm³⁺ co-doped tellurite glasses possessing excellent spectroscopic properties is a potential medium for mid-infrared laser.     

Desvitrification on an oxyfluoride glass doped with Tm3+ and Yb3+ ions under Ar laser irradiation

Desvitrification in a Tm³⁺ and Yb³⁺ codoped oxyfluoride glass has been obtained by exciting with a continuous Argon laser radiation increasing the average laser power from 144 to 2900 mW. Excitation spectra inside a locally damaged zone in a 1 mol% Tm³⁺ and 2.5 mol% Yb³⁺ codoped glass have been measured under excitation in the wavelength range 750–830 nm detecting the ²F_5/2 (Yb³⁺) level. This curve is the result of the contribution of two different kinds of centers, the fluoride nanocrystals and the glassy phase of the glass ceramic sample created due to the irradiation. The weight of the contributions of each of the centers depends on the excitation wavelength, and from the analysis of the decay of the luminescence it can be concluded that approximately 80% of the Tm³⁺ ions are located in the nanocrystals and therefore less than 20% in the glassy phase.     

2 μm emission properties in Tm3+/Ho3+ codoped fluorophosphate glasses

New type of fluorophosphate glasses with different Tm³⁺/Ho³⁺ doping concentrations have been prepared. From the measured fluorescence spectra, strong emission near 2 μm is demonstrated in the samples. Based on the absorption spectra, the Judd–Ofelt parameters and radiative properties were calculated and compared with those of other glass hosts. Then for our prepared Tm³⁺/Ho³⁺ codoped fluorophosphate glass, the higher predicted spontaneous transition probability (76.54 s^?1) along with the larger calculated emission cross-section (6.15×10^?21 cm²) gives evidence of intense 2 μm fluorescence. Besides, it is found that the optimum doping concentration is 4 mol% Tm³⁺/1 mol% Ho³⁺ for the strongest 2 μm emission in our prepared samples.     

Increase of the blue upconversion emission in YAG:Tm3+ nanopowders by codoping with Yb3+ ions

The YAG nanopowders were prepared by a co-precipitation method using nitrate and ammonium hydrogen carbonate as raw materials. To obtain homogenous precipitate, reverse-strike (adding salt solutions to the precipitant solution) technique was adopted. Therefore, single (Tm³⁺) and codoped (Tm³⁺–Yb³⁺) YAG nanopowders with a size between 40–90 nm have been obtained.Blue upconversion emission at around 480 nm has been found in YAG: Tm³⁺ nanopowders under excitation to the ³H₄ level of Tm³⁺ at around 800 nm. However, this upconversion emission in nanopowders codoped with Tm³⁺–Yb³⁺ ions is increased by a factor of about 10. The analysis of the temporal evolution of the involved levels and the dependence of the upconversion intensity on the pump power at 800 nm allowed to distinguish the upconversion mechanism. In YAG: Tm³⁺ nanopowders the upconversion mechanism is due to excited state absorption processes. However, in the codoped samples, Yb³⁺ ions acts as the sensitizers; in consequence, the blue upconversion is strongly increased.     

Spectroscopic properties of Tm3+/Ho3+ co-doped NaLa(WO4)2 single crystal

Tm³⁺/Ho³⁺ co-doped NaLa(WO₄)₂ single crystal was successfully grown by the Czochralski method. The crystal was characterized by room temperature absorption spectra, fluorescence spectra around 2 μm, up-conversion fluorescence and luminescence decay measurements. Spectroscopic properties related to the laser operation around 2 μm of Ho³⁺ ions have been evaluated. The energy level scheme and energy transfer processes of Tm³⁺ and Ho³⁺ were analyzed. The obtained spectroscopic results show the crystal is a potentially host for Ho³⁺ 2 μm infrared laser.     

Ho:LaF3 single crystal as potential material for 2 μm and 2.9 μm lasers

Optical properties of a Ho-doped LaF₃ single crystal have been detailed investigated as a promising material for 2 μm and 2.9 μm lasers for the first time. Judd–Ofelt theory was applied to analyze the absorption spectrum to determine the J–O intensity parameters Ω_t(t=2,4,6), based on which the emission probabilities, branching ratio and radiative lifetime for the as-grown crystal were all calculated. The stimulated emission cross-sections of the ⁵I₇ → ⁵I₈ and ⁵I₆ → ⁵I₇ transitions were obtained by using the Fuchtbauer–Ladenburg method. The gain cross-section for 2 μm emission becomes positive once the population inversion level reaches 30%. The Ho:LaF₃ crystal shows long fluorescence lifetime of ⁵I₇ manifold (25.81 ms) as well as ⁵I₆ manifold (10.37 ms) compared with other Ho³⁺-doped crystals. It can be proposed that the Ho:LaF₃ crystal may be a promising material for 2 μm and 2.9 μm laser applications.     

Fabrication and luminescence behavior of phosphate glass ceramics co-doped with Er3+ and Yb3+

Transparent phosphate glass ceramics co-doped with Er³⁺ and Yb³⁺ in the system P₂O₅Li₂OCaF₂TiO₂ were successfully synthesized by melt-quenching and subsequent heating. Formation of the nanocrystals was confirmed by X-ray powder diffraction. Judd–Ofelt analyses of Er³⁺ ions in the precursor glasses and glass ceramics were performed to evaluate the intensity parameters Ω_2,4,6. Under 975 nm excitation, intense upconversion (UC) and infrared emission (1545 nm) were observed in the glass ceramics by efficient energy transfer from Yb³⁺ to Er³⁺. The luminescence processes were explained and the emission cross section was calculated by Fuchtbauer–Ladenburg (F–L) formula. The results confirm the potential applications of Er³⁺/Yb³⁺ co-doped glass ceramics as laser and fiber amplifier media.     

Intense orange emission in Pr3+ doped lead phosphate glass

Spectroscopic properties of one mol% Pr₂O₃ embedded in 40%PbO–60%P₂O₅ glass have been investigated at room temperature. From the absorption spectra energy levels of the observed bands are assigned. Using free ion Hamiltonian theoretical values of energy of 13 multiplets of Pr³⁺ are calculated. Judd–Ofelt intensity parameters have been estimated by including and excluding the hypersensitive transition (³H₄→³P₂). The best set of Judd–Ofelt parameters are obtained by omitting ³H₄→³P₂ transition from the calculation. These parameters are used to evaluate the important laser parameters for various emission lines. Our investigation reveals that the present glass may be utilized as a laser active medium corresponding to ³P₀→³H₄ and ¹D₂→³H₄ transitions respectively, for 484.6 nm (blue) and 599.5 nm (strong orange) emissions. Indirect and direct optical band gap energies of Pr³⁺ doped lead phosphate glass matrix have also been reported.     

Spectroscopic characterization of Tm3+:TeO2–K2O–Nb2O5 glasses for 2-μm lasing applications

We have performed detailed experiments to investigate the spectroscopic properties of a new type of tellurite based host doped with thulium: Tm₂O₃:(0.70)TeO₂–(0.15)K₂O–(0.15)Nb₂O₅ having Tm₂O₃ concentrations of 0.125, 0.25, 0.5, and 1.0 mol%. By performing a Judd–Ofelt analysis of the absorption bands, we obtained average radiative lifetimes of 2.57±0.20 and 0.35±0.01 ms for the ³H₄ and ³F₄ levels, respectively. Furthermore, we also observed that an increase in the Tm₂O₃ concentration from 0.125 to 1.0 mol% results in a decrease of the measured fluorescence lifetime from 814 to 439 μs and from 258 to 47 μs for the ³H₄ and ³F₄ levels, respectively, due to efficient non-radiative decay. The highest quantum efficiency of 32% was obtained for the sample doped with 0.125 mol% Tm₂O₃ for the ³H₄ level. Results show that cross relaxation becomes important as the ion concentration is increased, leading to the quenching of the 1460-nm band and enhancement of the 1860-nm emission. The highest emission cross section of 6.85×10^?21 cm² measured for the 1860-nm band reveals the potential of this host for the development of 2-μm lasers in bulk glass as well as fiber media.     

A neodymium fluid laser: Laser emission in circulating state

Differing from conventional liquid lasers, a novel concept of fluid laser was provided, which has attractively potential using in high average power lasers. The laser medium was prepared by dispersing Nd³⁺: phosphate glass micro-balls in organic match liquid. Its optical properties were investigated and the radiative transition rate was calculated by Judd–Ofelt theory. The experiment of laser oscillation in static state indicates that the heat exchanging has limited effect on refractive index of the fluid laser medium in a short time. In circulating state, a laser oscillation occurred at 1058.1 nm when pumped by two 808 nm diode lasers. The maximum output energy is 2.58 mJ with the absorbed pumping energy of 460 mJ. This study offers a new way in the exploration of high average power laser.     

Optical spectroscopy and laser parameters of Zn2+/Er3+/Yb3+-tridoped LiNbO3 crystal

The Zn/Er/Yb:LiNbO₃ and Er/Yb:LiNbO₃ crystals were grown by the Czochralski technique. The laser characteristics of 1.54 μm emission were predicted based on the Judd–Ofelt theory, and the intensity parameters Ω_t (Ω₂=7.23×10^?20 cm², Ω₄=3.15×10^?20 cm² and Ω₆=1.43×10^?20 cm²) were obtained. The stimulated emission cross sections (σ_em) at 1.54 μm emission in Zn/Er/Yb:LiNbO₃ were calculated based on the McCumber theory and the Füchtbauer–Ladenburg theory. The gain cross section spectrum of Zn/Er/Yb:LiNbO₃ crystal was also investigated. Under 980 nm excitation, a lenghthening lifetime of 1.54 μm emission and an enhancement of green upconversion emission were observed for Zn/Er/Yb:LiNbO₃ crystal. The studies on the power pump dependence and the upconversion mechanism suggested that both green and red upconversion emissions were populated via the three-photon process, and Zn²⁺ ion tridoping increases the probability of cross relaxation process between the two neighboring Er³⁺ ions.     

Optical absorption and fluorescence studies of Dy3+-doped lead telluroborate glasses

Lead telluroborate (PTBDy) glasses doped with different Dy³⁺ ion concentrations were prepared by melt quenching technique and investigated through optical absorption, fluorescence and decay measurements. The Judd–Ofelt intensity parameters (Ω_λ) are obtained by a least square fit analysis. The small root mean square deviation of ±0.34×10^?6 shows a good fit between the experimental and calculated oscillator strengths. The radiative properties of the ⁴F_9/2→⁶H_13/2 emission transition of PTBDy10 glass are determined and compared to the other reported glasses. The variation of decay time of the ⁴F_9/2 emission state is attributed to the interaction among the excited Dy³⁺ ions at higher concentration. The PTBDy10 glass is found to be a suitable candidate for solid state laser materials to produce intense yellow (576 nm) luminescence through the ⁴F_9/2→⁶H_13/2 transition.     

Optical temperature sensor through infrared excited blue upconversion emission in Tm3 +/Yb3 + codoped Y2O3

An analysis of the intense blue upconversion emission at 476 and 488 nm in Tm^3 +/Yb^3 + codoped Y₂O₃ under excitation power density of 86.7 W/cm² available from a diode laser emitting at 976 nm, has been undertaken. Fluorescence intensity ratio (FIR) variation of temperature-sensitive blue upconversion emission at 476 and 488 nm in this material was recorded in the temperature range from 303 to 753 K. The maximum sensitivity derived from the FIR technique of the blue upconversion emission is approximately 0.0035 K^? 1. The results imply that Tm^3 +/Yb^3 + codoped Y₂O₃ is a potential candidate for the optical temperature sensor.     

Modeling and simulation of mid-IR amplifying characteristics of Tm3+-doped chalcogenide Photonic Crystal Fibers

This paper deals with the designing of a Tm³⁺-doped chalcogenide Photonic Crystal Fiber (PCF) amplifier operating in the mid-IR range. The chalcogenide glass of 72GeS₂–18Ga₂S₃–10CsI (in mol%) was fabricated with the high temperature melt-quenching method, which exhibited a strong emission peak around 3.8 μm under the excitation of a 800 nm laser. By employing the rate equations and propagation equations, the amplifying characteristics of the designed PCF amplifier were worked out. It is shown that the designed PCF amplifier exhibits a signal gain larger than 30 dB and a spectral width wider than 200 nm. The theoretical models and simulation results show that the PCF presented in this work can be used in developing high efficiency mid-IR light sources.     

Infrared fluorescence,energy transfer process and quantitative analysis of thulium-doped niobium silicate-germanate glass

Infrared fluorescence, energy transfer process, thermal stability and quantitative analysis of Tm³⁺ doped novel niobium silicate-germanate glasses have been investigated. The thermal stability changes indicate that the introduction of La₂O₃ to substitute for Nb₂O₅ can improve the anti-crystallization of present glass system. Intense 1.8 μm fluorescence has been achieved and the value of emission cross section can reach as high as 12.2 × 10⁻²¹ cm². Besides, the microparameters of energy transfer were analyzed by the extended overlap integral method. Hence, the results indicate that the excellent spectroscopic characteristics of this kind of silicate-germanate glass together with the good thermal properties may become a promising matrix applied for 1.8 μm band near-infrared laser.