Fluorescence Branching Ratios Research Articles

Polarized spectral analysis of Er 3+ ions in Er 3+:LiGd(MoO 4) 2 crystal

The Er 3+:LiGd(MoO 4) 2 crystal with Ø21 × 33 mm 3 was grown by the Czochralski technique, and the absorption spectra, the fluorescence spectra and the fluorescence decay curves were measured at room temperature. Some spectroscopic parameters, such as the parameters of oscillator strengths, the spontaneous transition probabilities, the fluorescence branching ratios, the radiative lifetimes and the emission cross-sections were estimated based on Judd–Ofelt theory and Füchtbauer–Ladenburg method. The infrared emission at 1450–1650 nm, due to 4I 13/2 → 4I 15/2 transition and the visible emission at 520–569 nm corresponding to 2H 11/2, 4S 3/2 → 4I 15/2 transition were observed in Er 3+:LiGd(MoO 4) 2 crystals under 979 nm excitation at room temperature. The emission cross-sections are 4.37 × 10 −20 cm 2 at 553 nm and 0.584 × 10 −20 cm 2 at 1561 nm for π-polarization, and the following measured lifetimes are 4.57 ms and 10.74 μs. The upconversion emissions were attributed to energy transfer between Er 3+ ions and the excited state absorption.

Polarized spectroscopic properties of Ho 3+ ions in NaLa(MoO 4) 2 crystal

A Ho 3+-doped NaLa(MoO 4) 2 single crystal was grown by the Czochralski method. The polarized absorption spectra, polarized fluorescence spectra, and fluorescence decay curves of the crystal were measured at room temperature. The spontaneous emission probabilities, radiative lifetimes, and fluorescence branching ratios of the typical fluorescence multiplets of Ho 3+ ions were calculated. The polarized stimulated emission and gain cross-sections of the 5 I 7 → 5 I 8 transition were obtained. The results show that the Ho 3+:NaLa(MoO 4) 2 crystal is a promising gain medium for tunable and ultrashort pulse lasers operating around 2.0 μm.

Optical parameters of Nd3+:Er3+:Yb3+ co-doped borosilicate glasses and their energy transfers at high temperature

This paper reports that a series of Nd3+:Er3+:Yb3+ co-doped borosilicate glasses have been prepared and their absorption spectra measured. The J—O intensity parameters Ωk (k = 2, 4, 6), spontaneous radiative lifetime τrad, spontaneous transition probability A, fluorescence branching ratio β and oscillator strength fed of the Nd3+ ions at room temperature are calculated based on Judd—Ofelt (J—O) theory. The temperature dependence of the up-conversion photoluminescence characteristics in a Nd3+:Er3+:Yb3+ co-doped sample is studied under a 978 nm semiconductor laser excitation, and the energy transfer mechanisms among Yb3+, Er3+ and Nd3+ ions are analysed. The results show that the J—O intensity parameters Ω2 increase when the Nd3+ concentration of the Nd3+:Er3+:Yb3+ co-doped borosilicate glasses increases. The possibility of spontaneous transition is small and lifetimes are long at levels of 4F5/2 and 4F3/2. The intensity of Nd3+ emissions at 595, 691, 753, 813 and 887 nm are markedly enhanced when the sample temperature exceeds 400 K. The reasons being the cooperation of the secondary sensitization from Er3+ to Nd3+ and the contribution of a multi-phonon.

Spectroscopic investigation of Dy3+-doped Li2Gd4(MoO4)7 crystal for potential application in solid-state yellow laser

Dy3+:Li2Gd4(MoO4)7 crystal with dimensions of ∅20×25mm3 has been grown by the Czochralski method. The spectroscopic properties of Dy3+:Li2Gd4(MoO4)7 crystal have been investigated. Based on the analysis of polarized absorption spectra in the framework of the Judd–Ofelt theory, the main spectroscopic characteristics, including the phenomenological intensity parameters, spontaneous transition probabilities, fluorescence branching ratios and radiative lifetimes of Dy3+ in the crystal, have been determined. The emission cross-sections for the 4F9/2→6H13/2 transition of special interest for laser application have been calculated using the Füchtbauer–Ladenburg (F–L) equation. The fluorescence and radiative lifetimes of 4F9/2 manifold are equal to 126.5μs and 201.1μs, respectively, which mean the quantum efficiency is 62.9%. The results propose the possibility of Dy3+:Li2Gd4(MoO4)7 crystal for solid-state yellow laser pumped by commercially available blue laser diodes.

Enhanced mid-IR emission in Yb 3+–Tm 3+ co-doped oxyfluoride glass ceramics

Tm 3+–Yb 3+ co-doped transparent oxyfluoride glass ceramics were prepared through thermal treatment of the as-prepared glasses. The precipitation of nanocrystals and the incorporation of Tm 3+ and Yb 3+ into the nanocrystals were confirmed by X-ray diffraction and absorption spectra. Based on the Judd–Ofelt theory, the J–O parameters Ω λ ( λ = 2, 4, 6), spontaneous radiative transition rates, radiative lifetimes and fluorescence branching ratios of Tm 3+ in both as-prepared glasses and glass ceramics were calculated. Intense mid-IR emission and upconversion luminescence in the Tm 3+ and Yb 3+ co-doped glass ceramics were observed under 980 nm excitation. Especially, compared with that of the as-prepared glasses, mid-IR luminescence intensity of Tm 3+ in the glass ceramics was greatly enhanced. Desirable spectroscopic characteristics suggest that these oxyfluoride glass ceramics may be promising mid-IR laser active medium.

Spectroscopic and photoluminescence properties of Dy 3+-doped lead tungsten tellurite glasses for laser materials

Lead tungsten tellurite (LTT) glasses doped with different Dy 3+ ion concentrations have been prepared and characterized through optical absorption, photoluminescence and decay measurements. The glassy nature of the LTT host has been confirmed through the XRD measurements. The three phenomelogical intensity parameters Ω λ ( λ = 2, 4, 6) have been determined from the absorption spectral intensities using the Judd–Ofelt (J–O) theory. The hypersensitivity of 6H 15/2 → 6F 11/2 transition based on the magnitude of Ω 2 parameter has also been discussed. By using the J–O intensity parameters several radiative properties such as spontaneous transition probabilities ( A R ), fluorescence branching ratios ( β R ) and radiative lifetimes ( τ R ) have been determined. The effect of Dy 3+ ion concentration on the emission intensities of 4F 9/2 → 6H J′ ( J′ = 15/2, 13/2, 11/2 and 9/2) transitions has also been reported.

Synthesis, growth, and characterization of Nd-doped SrGdGa3O7 crystal

A disordered Nd:SrGdGa3O7 (Nd:SGGM) laser crystal was grown by the Czochralski method. The space group and effective segregation coefficient of Nd3+ were determined to be P4¯21m and 1.36, respectively. Thermal properties, including the average linear thermal expansion coefficient, thermal diffusivity, specific heat, and thermal conductivity were measured. It was found that the thermal conductivity increases with increasing temperature, indicating glasslike behavior. Sellmeier’s equations were fitted by measuring the refractive indices in the range of 253–2325 nm. The polarization absorption and emission spectra were measured at room temperature, and Judd–Ofelt analysis was carried out to calculate the fluorescence branching ratios from the upper F43/2 state and the fluorescence lifetime. The stimulated emission cross section for the F43/2→I411/2 transition was calculated to be 2.00×10−20 cm2. Finally, a diode-pumped laser experiment at 1.06 μm is described. Thermal, optical, and laser properties have shown that Nd:SGGM crystals are promising for use as disordered laser materials.

Synthesis and luminescence properties of LiLa 1−xNd xP 4O 12 nanocrystals

The synthesis of Nd 3+ doped lithium lanthanide tetraphosphate (LiLaP 4O 12) nanocrystalline powders was presented. Their structure, morphology and spectroscopic properties are determined. The luminescence properties of LiLa 1− x Nd x P 4O 12 nanocrystalline powders were studied as a function of concentration of Nd 3+ ions. The fluorescence branching ratio of 4F 3/2 → 4I J transitions were strongly dependent on Nd 3+ concentration what was associated with self-absorption of the resonant fluorescence R 1 → Z 1 transition. It was found that the fluorescence quenching rate has demonstrated a linear concentration dependence.

Spectroscopic and upconversion properties of erbium-doped potassium lithium tantalate niobate crystals under 800 nm femtosecond laser excitation

The single crystals of tungsten bronze-type potassium lithium tantalate niobate doped with three concentrations erbium with good quality are grown using top-seed solution growth method. The unpolarized ultraviolet-visible-near infrared optical absorption spectra of these single crystals are measured at room temperature. The green and red upconversion emission properties are analyzed with respect to steady-state spectra and decay behaviors under 800 nm femtosecond laser excitation. The spectroscopic properties of Er3+ ions are studied on the basis of the Judd–Ofelt theory. 12 Er3+ ions absorption bands are observed ranging from 350 to 1650 nm, the lower limit is also the ultraviolet absorption edge of these crystals. The fluorescence branching ratio and radiative lifetime are calculated to support the upconversion mechanism. The relationship of the Judd–Ofelt parameters Ω4<Ω6 of Er3+ in these crystals is different from the general trend Ω2>Ω4>Ω6. Experimental results indicate that upconversion emission is a two-photon process. It follows that the shortening of lifetime and the increasing of intensities of red emission are due to the increase in Er3+ ions cluster sites. Excited state absorption and energy transfer processes lead to the green emission while cross relaxation process produces the red emission.

Optical-transition properties of the Nd 3+ ion in KLu(WO 4) 2 crystal

Optical absorption and emission intensities of Nd 3+ ion in KLu(WO 4) 2 crystal were investigated. Based on the Judd-Offelt theory, we calculated the following spectral parameters: phenomenological intensity parameters Ω 2=5.567×10 −20, Ω 4=3.597×10 −20, and Ω 6= 3.800×10 −20 cm 2. The radiative lifetime of levels 4F 3/2 was 182.58 μs. The fluorescence branching ratio for the transition 4F 3/2→ 4I 11/2 was 46.98%. In addition, the radiative transition probabilities A J,J', oscillator strengths P J,J' and the values of integrated emission cross sections were also calculated. In comparison with those of other laser crystals, these results indicated that Nd: KLuW is a promising efficient laser material.

The near- and mid-infrared emission properties of Tm 3+-doped GeGaS–CsI chalcogenide glasses

Serials of chalcogenide glasses based on composition of 72GeS 2–18Ga 2S 3–10CsI (in mol%) and doped with high Tm 3+ content (up to 10,000 ppm) were prepared, and their luminescence properties were investigated under excitation with 800 nm laser. The influences of doping concentration on Judd–Ofelt intensity parameter Ω i , spontaneous transition probability A, fluorescence branching ratio β, and radiative lifetime τ rad of Tm 3+ in the samples were studied. Four infrared emission bands observed were centered at 1.48, 1.8, 2.3, and 3.8 μm, corresponding to optical transitions 3H 4 → 3F 4, 3F 4 → 3H 6, 3 H 4 → 3 H 5 and 3H 5 → 3F 4, respectively. For 1.0 wt.% Tm 3+: doped sample, no concentration quenching was observed and its emission cross-sections at 2.3 and 3.8 μm calculated by using Füchtbauer–Ladenburg equation were 6.85 × 10 − 21 and 7.66 × 10 − 21 cm − 2, respectively.

Optical transition and upconversion luminescence in Er 3+ doped and Er 3+–Yb 3+ co-doped fluorophosphate glasses

Fluorophosphates glasses YF 3–BaF 2–Ba(PO 3) 2 doped with Er 3+ and Er 3+–Yb 3+ were prepared and the structures of the samples were briefly investigated. The experimental intensity parameters were calculated according to the Judd–Ofelt theory, from which the radiative transition probabilities, fluorescence branching ratios, and radiative lifetimes of Er 3+ were obtained. Bright green and red upconversion emissions was observed in Er 3+–Yb 3+ co-doped samples excited by 980 nm laser diode, and two-photons absorption processes were determined for the emissions by examining the dependence of the emission intensity on the excitation power. The concentration effects on the intensity and decay time of the upconversion emission revealed that growing Er 3+ concentration declined the probability of sequential energy transfer from Yb 3+ to Er 3+, and thus increasing the intensity ratio of the red emission to the green ones. The temperature effects on the intensity ratios of different emission bands showed that the maximum transducer sensitivity based on the fluorescence intensity ratio (FIR) was calculated to be 0.0015/°C at 6 °C.

Growth, spectroscopic properties and laser performance of Nd 3+-doped potassium ytterbium tungstate laser crystal

The 5 at.% Nd 3+-doped potassium ytterbium tungstate (Nd 3+:KYb(WO 4) 2, hereafter Nd:KYbW) laser crystal with the dimension up to 28 mm × 15 mm × 12 mm was grown by the top seeded solution growth (TSSG) method. The infrared spectrum of crystal sample was measured, and the vibrational peaks were assigned. According to the absorption and emission spectra of crystal sample, the absorption and emission cross-sections are 16.03 × 10 −20 cm 2 at 808 nm and 10.72 × 10 −20 cm 2 at 1067 nm, respectively. The fluorescence life of 4F 3/2 energy level is 196.33 μs, and the fluorescence branching ratio for the 4F 3/2– 4I 11/2 transition at 1067 nm is 55.74%. The energy transfer between Nd 3+ and Yb 3+ ions was observed from the fluorescence spectra pumped by 808 and 980 nm LD sources and the Stark levels of Yb 3+ in Nd:KYbW crystal were determined. Highly efficient laser output up to 305 mW of Nd:KYbW crystal at 1067 nm has been achieved under pumping by a CW 808 nm laser diode at room temperature. The optical–optical conversion efficiency is 33.9% and the slope efficiency is 46.8%.

Conversion of infrared radiation into visible emission in NaY(WO 4) 2:Yb 3+, Ho 3+ crystal

The spectroscopic characteristics and fluorescence dynamics for Yb 3+/Ho 3+:NaY(WO 4) 2 crystal were investigated. The parameters of oscillator strengths, the spontaneous transition probabilities, the fluorescence branching ratios, the radiative lifetimes and the stimulated emission cross sections have been calculated based on Judd–Ofelt theory and Füchtbauer–Ladenburg method. The energy transfer efficiency from Yb 3+ to Ho 3+ was 65.85%. The green emission (530–570 nm) corresponding to ( 5F 4, 5S 2)→ 5I 8 transition, red emission (640–670 nm) due to 5F 5→ 5I 8 transition and NIR emission (740–770 nm) attributed to ( 5F 4, 5S 2)→ 5I 7 transition were observed on 974 nm excitation at room temperature. Under low pump power, the intensity of green light emission is weaker than that of the red light, while under high pump power, the case is on the contrary. The upconversion is based on the two-photon process either the energy transfer from Yb 3+ ions or by the excited state absorption. The proposed mechanisms of upconversion emissions were provided.

Optical spectroscopy of Er:YSGG laser crystal

Er:YSGG single crystals with good optical quality were grown by Czochralski method. X-ray diffraction (XRD) measurements show that the crystal lattice parameters of the 30 at.% Er 3+-doped YSGG crystal were a= b= c=12.4640±0.0065 Å, α= β= γ=90°. The doping concentration of Er 3+ in YSGG was calculated. The absorption spectrum and photoluminescence spectra of Er:YSGG crystal were studied at room temperature. Based on Judd–Ofelt (J–O) theory, the J–O intensity parameters Ω t ( t=2, 4, 6), the experimental and theoretical oscillator strengths were calculated using the absorption spectrum. The intensity parameters Ω t ( t=2,4,6) obtained to be Ω 2=0.23×10 −20 cm 2, Ω 4=0.86×10 −20 cm 2, Ω 6=0.37×10 −20 cm 2, respectively. With these intensity parameters, the line strengths, oscillator strengths, transition probabilities, fluorescence branching ratios and radiation lifetimes were calculated. The photoluminescence spectra and excitation spectrum of Er:YSGG were measured and studied.

Growth and anisotropic spectral properties of Er:YAlO 3 crystal

A high quality Er 3+-doped YAlO 3 single crystal has been successfully grown with the Czochralski method by a radio-frequency heating system. The polarized absorption and polarized fluorescence spectra are measured at room temperature. The effective phenomenological intensity parameters are obtained by analysis of the polarized absorption spectra with Judd–Ofelt (J–O) theory, and the results are: Ω 2 , e f f = 2.83 × 10 − 20 c m 2 , Ω 4 , e f f = 1.39 × 10 − 20 c m 2 , and Ω 6 , e f f = 1.29 × 10 − 20 c m 2 . The spontaneous emission probabilities, fluorescence branching ratio and radiative lifetime of Er 3+ ions in YAP crystal are calculated with the obtained parameters. The polarized emission cross-sections of the I 13 / 2 4 → I 15 / 2 4 transition are calculated by both the Fuchtbauer–Ladenburg formula and the reciprocity method, and the results are compared.

Spectroscopic properties and Judd-Ofelt theory analysis of La, Nd codoped Y2O3 high refractivity transparent ceramics

Nd，La:Y2O3 nanocrystalline powder was prepared by co-precipitation method. The transparent ceramic was fabricated by vacuum sintering at 1700℃ for 4 h in vacuum. Transparent polycrystalline ceramics with uniform lanthanum distribution was obtained. The grain size was around 22 μm. No pores were found in the grain and grain boundary. The absorption spectrum and the fluorescence spectrum of the sample were measured. The highest absorption peak is centered at 821 nm and the absorption cross section is 43×10-24 m2 The main emission peak is at 1078 nm, and the fluorescence lifetime is 0287 ms. The Judd-Ofelt intensity parameter Ωλ（λ=2，4，6）, spontaneous transition probability, radiative lifetime and fluorescence branching ratio of Nd3+ were calculated by Judd-Ofelt theory. The calculated emission cross section of 4F3/2→4I11/2 transition is 20×10-24 m2 It was found that the addition of La ion can change the crystalline field of yttria, which helps to obtain suitable solid laser materials.

Growth and optical properties of Pr 3+:La 2CaB 10O 19 crystal

Pr 3+ doped La 2CaB 10O 19 crystal were grown by the top-seeded solution growth (TSSG) method. The absorption spectra, emission spectra and lifetime were measured at room temperature. The J-O parameters (Ω t , t=2,4,6), the radiative transition probabilities A J, J' , oscillator strengths P J, J' , radiative lifetime τ, fluorescence branch ratios β J and the value of integrated emission cross section have also been calculated. Five main absorption bands, 3H 4 to 3P 1+ 3P 2, 3P 0, 1D 2, 3F 3 + 3F 4 and 3F 2, were observed in the absorption spectra. The 1G 4 absorption band was not observed. A very strong emission band at 601 nm ( 1D 2 → 3H 4) was observed in the emission spectra. The experimental lifetime for this level was compared with that obtained theoretically by using J-O approach.

JUDD–OFELT THEORY ANALYSIS AND SPECTROSCOPIC PROPERTIES OF Ho:LiNbO3

A series of Ho : LiNbO 3 crystals with various concentration of Ho 2 O 3 were grown by Czochralski technique. Transmittance spectrum, absorption spectrum and modified Judd–Ofelt approach have been used to investigate its spectroscopic properties. Ho concentrations in crystals were analyzed by an inductively-coupled plasma optical emission spectrometry (ICP-OE/MS). The results of the spectroscopic analysis of transition strengths for Ho ion in a series of Ho : LiNbO 3 crystals with various Ho content are reported. It is concluded that all the Ωλ values of the Ho ion decrease with increasing Ho content. For Ho (4 mol%): LiNbO 3, the obtained intensity parameters and radiative lifetime of the 5 I 5 level are: Ω2=5.75×10-20 cm2, Ω4=22.69×10-20 cm2, Ω6=14.10×10-20 cm2, and τ=4.08 ms respectively. The results showed that the Ho 2 O 3-codoped LiNbO 3 crystal increases the Ho ion radiative lifetimes, but has less influence on the fluorescence branching ratio.

Synthesis and optical properties of infrared-emitting YF3:Nd nanoparticles

Nd 3 + -doped YF3 (YF3:Nd) nanoparticles with a size of ∼20 nm were synthesized by solvothermal decomposition of yttrium and neodymium trifluoroacetate precursors in oleylamine. Using the 4f-energy matrix diagonalization procedure various interaction parameters: Slater–Condon (F2, F4, and F6), spin-orbit (ξ), two body interaction (α, β, and γ), Judd parameters (T2, T3, T4, T6, T7, and T8), spin-other-orbit parameters (M0, M2, and M4) and electrostatically correlated spin-orbit interaction parameters (P2, P4, and P6), and the crystal-field parameters (Bqk) were evaluated. The potential of YF3:Nd as a laser host for 1052 nm emission was evaluated by quantitative analysis of the absorption, emission spectra, and fluorescence decay characteristics. Judd–Ofelt parametrization was employed to compute the radiative spectral parameters such as radiative transition probabilities, fluorescence branching ratios, stimulated emission cross sections, and quantum efficiencies of the observed bands in the fluorescence spectrum. Using the measured radiative properties, 75% quantum efficiency was obtained for the principal emission band at 1052 nm when the Nd dopant concentration was 0.25 mol %, with an emission cross section of 0.74×10−20 cm2. Analysis of the energy transfer kinetics showed that at low dopant concentrations of 0.25 mol % dipole-dipole interactions were dominant, whereas energy migration was the leading process at higher dopant concentrations. Quenching by OH impurities was found to be within the limit of optimum amplifier performance where multiphonon relaxation losses were negligible. Preliminary optical characterization showed that these nanocrystalline materials can be potentially used as optical amplifiers and in applications like infrared imaging, security and authentication.