Sijun Fan

Spectroscopic properties of thulium ions in bismuth silicate glass

A new type of bismuth silicate glass (Bi2O3-SiO2-ZnO-Al2O3-La2O3) doped with Tm2O3 is prepared by melt-quenching method. The thermal stability of the glass is examined by differential scanning calorimetry. No crystallization peak is found. Using the absorption and emission spectra, the absorption and emission cross-sections are calculated. Their maximum data are 2.9×10-21 cm2 at 1 663 nm and 4.7×10-21 cm2 at 1 826 nm, respectively. Using the Judd-Ofelt theory, the radiation transition probabilities and radiative lifetimes are obtained. The extended overlap integral method is applied to analyze energy transfer process among the Tm3+ ions. The transfer constants of cross-relaxation and energy migration among the Tm3+ ions at the 3H4 level are 7.60×10-40 and 14.98×10-40 cm6/s, respectively. The critical transfer radius for cross-relaxation is 0.99 nm. The cross relaxation process is easy to realize and is favorable for obtaining ~2-μm laser.

Compositional dependence of the 1.8 μm emission properties of Tm3+ ions in silicate glass

The compositional dependence of the 1.8 μm emission properties of Tm3+ ion-doped lead silicate glasses is investigated. Judd–Ofelt parameters are calculated and their variation with different glass modifier ions is obtained. The Judd–Ofelt parameters increase with decreased modifier ionic radius. A large spontaneous emission probability and a large emission cross-section are found to be related with the strength of the modifier ion. Fluorescence spectra are analyzed using rate equations and compared with recorded data. The results are very close, indicating the reliability of this method. Non-radiative probability is deduced by fitting the fluorescence decay curve; it becomes smaller with increased ionic field strength. Energy transfer processes are studied using the extended overlap integral method.

Tunable white light emission from γ-irradiated Ag/Eu co-doped phosphate glass phosphor

We report a new tunable white light emission from γ-irradiated Ag/Eu co-doped phosphate glass phosphor. The appearance of Eu2+ and silver aggregates after γ-irradiation was confirmed via Electron paramagnetic resonance (EPR), absorption, and emission spectra. The effects of Ag/Eu doping concentration and excitation wavelengths on white light emission were discussed. A pure white light emission with the chromaticity coordinates (X = 0.331, Y = 0.329) was generated using the optimal sample under excitation at 360 nm.

Highly stable and efficient pure green up-conversion emission of rod-like β-NaGdF4:Yb3+,Ho3+ submicro-crystals via ion-exchange for fluorescent labeling

High purity green up-conversion (UC) materials have wide applications in fluorescent labeling, plastic recycling and displays, etc. However, Yb3+/Er3+-based UC materials exhibit poor color purity of green light, and their output color is normally unstable under a variable excitation power density, which hinders their application in the aforementioned areas. Herein, we report the highly stable and efficient pure green UC of rod-like β-NaGdF4:Yb3+,Ho3+ submicro-crystals synthesized via a newly developed ion-exchange modified (IEM) method. IEM-derived NaGdF4:Yb3+,Ho3+ monodisperse submicro-crystals present not only a high-purity green output color (due to the large intensity ratio of green to red, IGreen/IRed ≈ 5) but also excellent color stability under varying conditions, such as excitation power density and doping concentration of Yb3+/Ho3+. More importantly, IEM arouses an enormously enhanced UC emission intensity of ∼3700-fold that of the precursor crystals (PC). The UC emission intensity of IEM β-NaGdF4:Yb3+,Ho3+ is ∼4 times stronger than that of its high temperature annealing (HTA) counterpart. The emission intensity of the single green band is ∼40% stronger than that of the IEM β-NaGdF4:20%Yb3+,2%Er3+ submicro-crystals. A proof-of-concept fluorescent labeling of clover patterns (15 × 12 mm) printed from NaGdF4:Yb3+,Ho3+ ink with stable and high purity green fluorescence is demonstrated under excitation with various power densities.

Distribution of electric field and energy flux around the cracks on the surfaces of Nd-doped phosphate glasses

We simulate and calculate numerically the electromagnetic field and energy flux around a surface crack of an Nd-doped phosphate laser glass by using the finite-difference time-domain method. Because of a strong interference between the incident wave and the total internal reflections from the crack and the glass surface, the electric field is redistributed and enhanced. The results show that the electric-field distribution and corresponding energy flux component depend sensitively on the light polarization and crack geometry, such as orientation and depth. The polarization of the incident laser beam relative to the crack surfaces will determine the profile of the electric field around the crack. Under TE wave incidence, the energy flux peak is always inside the glass. But under TM wave incidence, the energy flux peak will be located inside the glass or inside the air gap. For both incident modes, the light intensification factor increases with the crack depth, especially for energy flux along the surface. Because cracks on the polished surfaces are the same as the roots extending down, the probability for much larger intensification occurring is high. The results suggest that the surface laser-damage threshold of Nd-doped phosphate may decrease dramatically with subsurface damage.

Absolute up-conversion quantum efficiency reaching 4% in β-NaYF4:Yb3+,Er3+ micro-cylinders achieved by Li+/Na+ ion-exchange

Absolute quantum efficiency (QE) of up-conversion (UC) materials is still limited to ∼3%, which strongly limits their applications in many areas. Herein, we report highly efficient UC β-NaYF4:Yb3+,Er3+ micro-cylinders prepared via a newly developed Li+/Na+ ion exchange method (IEM) with absolute QE as high as ∼4.0%. A small amount of Li+ is interstitially incorporated in β-NaYF4:Yb3+,Er3+, which not only maintains well the micro-cylindrical morphology but also enhances the emission intensity by ∼40%, doubles absolute UCQE (∼3.0% under a fixed excitation power density of 15 W cm−2), and prolongs the lifetime. The UC excitation profile is composed of a sharp peak at 976 nm and a weak shoulder at 935 nm. The absolute UCQE of Li+/Na+ IEM β-NaYF4:Yb3+,Er3+ is systemically studied over a wide excitation power density of 0.4–100 W cm−2, and we obtained impressively high UCQE of 4.0% under 60 W cm−2 power density, which is among the highest values in the literature. The application of two green UC emissions of Li+/Na+ IEM β-NaYF4:Yb3+,Er3+ in ratiometric thermometers is successfully demonstrated. The high relative temperature sensitivity (SR) of 1113/T2 and excellent repeatability as indicated by three heating–cooling cycles (293–753 K) suggest their promising application as a temperature sensor.

Spectral Properties of ~2 μm Emission of Tm3+ Doped Bi2O3-SiO2-PbO Glass: Spectral Properties of ~2 μm Emission of Tm3+ Doped Bi2O3-SiO2-PbO Glass

用高温熔融法制备了Tm 2 O 3 摩尔掺杂浓度分别为0.1%、0.25%、0.5%、0.75%和1%的33Bi 2 O 3 -50SiO 2 -17PbO玻璃。采用DSC方法对该种玻璃的析晶性能进行研究, 发现其 T x – T g 为138℃, 说明该玻璃抗析晶性能良好。基于其吸收光谱, 采用Judd-Ofelt理论计算了Tm 3+ 离子的J-O参数和部分激发态能级的跃迁几率、荧光寿命和分支比等光谱参量。分析 3 F 4 能级寿命随掺杂浓度变化关系, 发现产生自淬灭的临界浓度为3.54×10 20 ions/cm 3 。用McCumber理论计算在33Bi 2 O 3 -50SiO 2 -17PbO玻璃中Tm 3+ 离子 3 F 4 → 3 H 6 能级跃迁的吸收截面和发射截面, 最大吸收截面和最大受激发射截面分别为3.7×10 -21 和7.2×10 -21 cm 2 。研究结果表明33Bi 2 O 3 -50SiO 2 -17PbO玻璃具有较好的光谱性质, 是一种实现~2 μm激光的较理想玻璃基质。用高温熔融法制备了Tm 2 O 3 摩尔掺杂浓度分别为0.1%、0.25%、0.5%、0.75%和1%的33Bi 2 O 3 -50SiO 2 -17PbO玻璃。采用DSC方法对该种玻璃的析晶性能进行研究, 发现其 T x – T g 为138℃, 说明该玻璃抗析晶性能良好。基于其吸收光谱, 采用Judd-Ofelt理论计算了Tm 3+ 离子的J-O参数和部分激发态能级的跃迁几率、荧光寿命和分支比等光谱参量。分析 3 F 4 能级寿命随掺杂浓度变化关系, 发现产生自淬灭的临界浓度为3.54×10 20 ions/cm 3 。用McCumber理论计算在33Bi 2 O 3 -50SiO 2 -17PbO玻璃中Tm 3+ 离子 3 F 4 → 3 H 6 能级跃迁的吸收截面和发射截面, 最大吸收截面和最大受激发射截面分别为3.7×10 -21 和7.2×10 -21 cm 2 。研究结果表明33Bi 2 O 3 -50SiO 2 -17PbO玻璃具有较好的光谱性质, 是一种实现~2 μm激光的较理想玻璃基质。