Intensity Parameters Ωt Research Articles

Spectral analysis of new-wavelength transitions originated from 1D2 level of Pr:YLF crystal

This work was dedicated to studying spectral characteristics of LiYF4 crystals, doping with different concentrations of Pr3+ in the range from 0.3 to 2.0 at.%. The polarized absorption spectra, emission spectra and fluorescence decay curves were investigated detailly. By introducing the Judd-Oflet (J-O) method, J-O intensity parameters Ωt (t=2,4,6) and radiative lifetimes were calculated. Moreover, to characterize 1D2 near-infrared (NIR) emission characteristics, emission cross sections σem and optical gain factors σemτf were further analyzed. The results show that 2.0 at.% Pr:YLF crystal is a better candidate for near-infrared transitions, having the highest absorption coefficient at 593.5 nm and the largest emission cross sections within these crystals.

Growth of Tm:Lu3Al5O12 single crystal fiber from transparent ceramics by laser-heated pedestal method and its spectral properties

Abstract Tm:Lu3Al5O12 (Tm:LuAG) single crystal fiber (SCF) with a diameter of 0.6 mm and a length of 140 mm was grown from transparent ceramics by laser-heated pedestal growth (LHPG) method. The growth, Tm3+ ion distribution, absorption spectrum, Judd-Ofelt (J-O)parameter and emission spectrum of SCF are discussed in detail. The test results show that the diameter fluctuation of the SCF is less than 2% and the Tm3+ ion distribution is relatively uniform. J-O theory was applied to analyze the absorption spectrum. With the J-O intensity parameters Ωt(t=2,4,6), the emission probabilities, fluorescence branching ratios and radiative lifetimes for the Tm:LuAG SCF and transparent ceramic were all calculated. The stimulated emission cross-section of the3F4→3H6 transition was obtained by using the Fuchtbauer-Ladenburg (F-L) method. After comparison, it is found that the spectral performance of Tm:LuAG SCF has been improved to a certain extent on the basis of transparent ceramics. It has the potential to be applied to fiber lasers.

Peak stimulated emission cross sections and quantum efficiencies of Sm3+ and Sm3+-Eu3+ co-doped bismuth boro-tellurite glasses

The effect of host glass composition and co-doping with Eu3+ on the optical properties of Sm3+ has been investigated in bismuth boro-tellurite glasses. The intensity parameters Ωt (t = 2,4,6), radiative transition probability (Arad) and radiative lifetimes (τrad) are obtained from optical absorption studies. Excitation spectra show that there exists energy transfer from Sm3+ to Eu3+ and vice versa. From fluorescence studies, fluorescence decay time (τexp), radiative quantum efficiencies (η), branching ratios (β) and peak stimulated emission cross section (σp) are obtained. The highest η of Sm3+ doped bismuth boro-tellurite glasses is found to be 60% and for Sm3+-Eu3+ co-doped glasses, it is 74%. Changing the host glass composition and co-doping with Eu3+ ions, the η of the glasses can be improved. The σp of Sm3+-Eu3+ doped glasses is found to be larger than that of singly doped Sm3+ glasses. Our results indicate that modifying the host glass composition and co-doping with Eu3+ can improve the emission characteristics of Sm3+ ions. Bismuth boro-tellurite glasses with enhanced values for η and σp are suitable for photonic devices and photovoltaic applications.

Effect of Er3+ concentration on spectral characteristic and 2.79 μm laser performance of Er:YSGG crystal

Er3+-doped YSGG crystals with nine different concentrations were grown successfully by Czochralski (Cz) method. The absorption, emission spectra, and the fluorescence decay curves are investigated comparably. Based on Judd–Ofelt (J–O) theory, the J–O intensity parameters Ωt (t = 2, 4, 6), the experimental and theoretical oscillator strengths are calculated with the absorption spectra. The results show that the 1 at. % lowly Er3+-doped YSGG crystal is more properly used in up-conversion laser applications and 5 at. % Er:YSGG crystal is a better candidate for 1.5 μm lasers within these nine crystals, while the heavily Er3+-doped YSGG crystal is beneficial for the 2.7 μm laser output. But if the doping concentration goes too high, the up-conversion rate of the 4I11/2 level could be higher than that of the 4I13/2 level, which would lead to increasing the up-conversion emission and quenching the mid-infrared emission. The 2.79 μm laser performance of LD end-pumped 40 at. % Er:YSGG crystal is also demonstrated.

Effect of the phosphate content on the spectroscopic and lasing properties of Er3+/Yb3+-doped fluorophosphate glasses

The influence of phosphate content on the formation and luminescent properties of Er3+/Yb3+-doped fluorophosphate glass has been studied. Using the Judd-Ofelt theory the phenomenological intensity parameters Ωt (t = 2; 4; 6) were obtained. The change of Judd-Ofelt parameters indicates minor differences in Er3+environment with increase in the phosphates content up to 10 mol.%. It was shown that in the studied fluorophosphates glasses erbium ions remain in the fluoride environment. The increase in phosphate content leads to lifetime change of erbium laser level from 9.4 ms to 7.8 ms. Using the Judd-Ofelt intensity parameters Ωt the stimulated emission cross-section of the 4I13/2→4I15/2 transition has been calculated. The gain shape of the glasses with lower (2–10 mol. %) phosphate content has been found to be smoother than for phosphate glasses with 20 mol.% Ba(PO3)2, which makes former very attractive gain material.

Optical studies on Tb3+: Dy3+ singly and doubly doped Borosilicate glasses for white light and solid state lighting applications

Host (H), Singly and co-doped Dy3+/Tb3+ ions borosilicate glasses (S1-S7) were fabricated by a traditional melt-quenching-annealing method to investigate their luminescence properties as well as their suitability for the development of SSL (solid-state lighting) and W-LEDs (white light-emitting diodes). The X-ray diffraction profile indicates the amorphous structure nature of the prepared glasses. The J-O (Judd-Ofelt) intensity parameters Ωt(t=2,4,6) are evaluated for both singly Dy3+, Tb3+ doped glasses according to their absorption spectrum. The Ω2 parameter of Dy3+ ion has higher value which indicates a higher degree of Dy3+ covalency and the neighbour ligands while Tb3+ ion in a lower degree of covalency where its Ω2 has low value. Also the radiative parameters for both singly doped ions (S1 and S2) are computed like probability of transition (AT), branching ratio (βr) and radiative lifetime (τr) for different bands. Further, both singly doped glasses reflects good properties for lasing application where the 4F9/2 manifold of S1 (0.5 mol% Dy3+) has radiative lifetime (τr) value of 1376 µs and higher value of (AT:447.02 s−1) in addition to branching ration of (βr:61.5%) for the (4F9/2→9H13/2) transition (576 nm). At the same time, S2 (0.5 mol% Tb3+) glass show a higher lifetime (τr:3753) for 5D4 level and (AT: 92.94 s−1) while the branching ratio for 5D4→7F5 band at 546 nm wavelength is (βr: 34.9%). The radiative emission properties were investigated according to the Tb3+ concentration increments. The mutual energy transfer (ET) occurrence between both ions (Dy3+, Tb3+) is demonstrated through the varying of their emission intensities. Furthermore, The chromaticity (x,y) color coordinates were evaluated according to the emission spectra of aforementioned glasses under excitation of 368 nm and 348 nm were found to be located in the white light color region of the CIE chromaticity color diagram. Also, from color-coordinated the color correlated temperature (CCT) is computed were found to be at high values (>4000). Thus, the fabricated glasses are suggested as a useful luminescence material for solid-state lightening as well as cool white light applications.

Spectroscopic properties of thulium doped (Lu0.25Gd0.75)2SiO5 (LGSO) single crystals

In this work, spectroscopic properties of (Lu0.25Gd0.75)2(1-x)Tm2xSiO5 (x = 0.04 and 0.005) single crystals were investigated. The material was found to be biaxial, exhibiting strong optical anisotropy, as clearly demonstrated in polarized absorption and emission spectra. Data from room temperature polarized absorption spectra were used in calculations within the phenomenological Judd-Ofelt model. The intensity parameters Ωt were established at Ω2 = 3.24 (±0.58), Ω4 = 2.96 (±0.24) and Ω6 = 0.86 (±0.14) [10−20 cm2]. The values of fluorescence lifetimes of the 1D2 and 1G4 levels were measured and subsequently compared with those calculated using the Judd-Ofelt theory. The strong absorption bands located at wavelengths around 355, 460 and 790 nm, related to the 3H6 → 1D2, 1G4, 3H4 transitions, were found suitable for optical pumping of the investigated material. The characteristics of emission spectra recorded in the blue (ca. 455 nm) and IR (ca. 1750 nm) regions indicate that further investigations of stimulated emission within those wavelength ranges are well justified and can be considered promising.

Structural and optical study of erbium doped borophosphate glasses

Borophosphate (BP) glass having composition of 50P2O5 - 10B2O3 - 20ZnO - 20PbO - xEr2O3 in mole %, where x= (0, 0.005, 0.01, 0.015, 0.02, 0.025 wt. %) were prepared by the melt quench method. X-ray analysis was performed to confirm the amorphous structure of the glass network. All glasses exhibit good transparency as observed from the naked eye. UV-VIS-NIR absorption spectroscopy was performed between 300 nm–1600 nm to probe the absorption bands of prepared samples. Ten major absorption peaks were appeared due to the excitation from ground level 4I15/2 to various excited states. The absorption spectrum was then used to calculate the direct and indirect band gap energy that lies within the range of 3.98 eV–4.32 eV and 3.86 eV–4.23 eV respectively. Refractive index and density were calculated in the range of 2.125–2.197 and 3.923–4.231 g/cm3 respectively. Judd-Ofelt (JO) theory was applied to investigate the radiative properties. JO intensity parameters Ωt (t = 2, 4, 6) were calculated by least square fitting method. The result shows that studied samples are suitable candidates for green light emission solid-state laser device.

Growth and investigation of Sm3+-doped GLSO crystal for visible laser application

Recently, an intense interest has been aroused for Sm3+-doped laser crystals which are able to realize visible reddish-orange laser directly using semiconductor laser pumping. In this study, a mixed Sm3+-doped Sm0.02Gd1.88La0.1SiO5 (Sm:GLSO) laser crystal was grown successfully by Czochralski method. The structure of the as-grown crystal was determined with X-ray diffraction. The as-grown crystal exhibits large absorption cross section (1.53 × 10−20 cm2) at around 405 nm, indicating that it can be pumped efficiently by the commercialized GaN/InGaN laser diode. Three Judd-Ofelt intensity parameters Ωt (t = 2, 4, 6) were calculated to be 5.177, 3.783 and 2.218 × 10−20 cm2, respectively. The stimulated emission cross section at 614 nm was calculated to be 0.471 × 10−20 cm2 and the fluorescence lifetime for 4G5/2 level was fitted to be 1.90 ms. All these results suggest that Sm:GLSO is very promising for realizing reddish-orange laser operation using the current commercialized GaN/InGaN laser diode pumping.

Spectroscopic and lasing properties of Er3+/Yb3+-doped fluorophosphate glass with small additives of phosphates

The influence of lead fluoride on the formation and luminescent properties of glass and glass-ceramics has been studied. Using the Judd-Ofelt theory, the intensity parameters Ωt have been obtained. The stimulated emission cross-section of the 4I13/2→4I15/2 transition has been determined. The energy transfer from ytterbium to erbium with 96% efficiency was found with an erbium laser level lifetime of ∼8 ms. The gain shape of the glass under study has been found to be smoother than for phosphate glasses, which makes the former very attractive gain material for ultra-short laser sources. For the first time, fluorophosphate glass-ceramics were obtained with nanocrystals doped with erbium and ytterbium ions.

Enhanced gain bandwidth of Tm3+ and Er3+ doped tellurite glasses for broadband optical amplifier

In this work, (90-x-y)TeO2-10GeO2-(x)Tm2O3-(y)Er2O3 composition of germano-tellurite glasses were synthesized by traditional melting and quenching technique and the spectroscopic properties of synthesized glasses were investigated. The values of Judd-Ofelt (JO) intensity parameters (Ωt(t = 2,4,6)), spontaneous transition probabilities (Α), branching ratios (β) and radiative lifetimes (τR) were obtained by using the Judd-Ofelt (JO) theory and absorption spectra. The stimulated emission cross-sections of TG:Tm and TG:Er glasses in 1.47 μm and 1.53 μm wavelength regions were calculated by Füchtbauer-Ladenburg formula and McCumber theory, respectively. The gain bandwidth-cross section product of TGTm0.5 and TGEr1 glasses was found to be 445.76 × 10−28 cm3 and 849 × 10−28 cm3, respectively. The fluorescence lifetime measurements were done for the 3F4 and 4I13/2 levels to compare with the radiative lifetimes. These results suggest that the TG:Tm and TG:Er studied glasses can potentially possess wider gain bandwidth for S-band amplifier and broadband optical amplifier WDM at 1.53 μm, respectively.

Influence of BaX2 (X = Cl, F) and Er2O3 concentration on the physical and optical properties of barium borate glasses

Er3+ ions doped oxyhalide barium borate glasses were prepared by means of conventional melt quenching technique. In the studied glass system, besides the Er3+ doping, barium oxide was partially replaced by BaF2 and/or BaCl2. The amorphous nature of as-prepared glasses was confirmed by X-ray diffraction patterns. The effects of the compositional changes were investigated through spectroscopic techniques such as optical absorption, emission and decay lifetime. It was found that the luminescence and decay lifetime of Er3+: 4I13/2 → 4I15/2 transition are affected by both Er3+ doping and halide insertions. By applying the Judd-Ofelt (JO) theory, the JO intensity parameters (Ωt, t = 2, 4, and 6) were calculated, and the trend Ω2 > Ω4 > Ω6 was found, which is in accordance with previous studies. Optical properties such as electric and magnetic dipole transition probabilities, fluorescence branching ratios, integrated emission cross sections and radiative lifetimes were also obtained and discussed for many excited states of Er3+ ions. The lifetime of the 4I13/2 excited level was measured and compared with the calculated one.

Dy3+ doped calcium boroaluminate glasses and Blue Led for smart white light generation

Dy2O3 doped calcium boroaluminate (CaBAl) glasses (50) B2O3-(25-x) CaO-(15) Al2O3-(10) CaF2-(xDy2O3) (x = 0.0, 0.5, 1, 2, 3, and 5 wt%) were prepared by using the conventional melt-quenching technique and characterized through XRD, FTIR, refractive index, volumetric density, absorption, excitation, photoluminescence and lifetime measurements. The amorphous nature of the CaBAl glasses was confirmed through XRD measurements. FTIR analysis allowed identifying stretching and bending vibrations of different borate groups. Absorption spectra presented characteristic peaks of Dy3+, corresponding to transitions from the 6H15/2 ground state to the excited energy levels. Oscillator strengths and Judd–Ofelt intensity parameters (Ωt = 2, 4 and 6) were calculated from the absorption spectra. The photoluminescence spectra of the Dy3+ doped CaBAl glasses, under 405 nm excitation, exhibited two intense emission bands corresponding to the 4F9/2 → 6H15/2 (blue) and 4F9/2 → 6H13/2 (yellow) transitions. The intensity of Dy3+ emission spectra increased with Dy2O3 content from 0.5 wt% to 3 wt% and concentration quenching was observed for concentrations higher than 3 wt%. The yellow/blue (Y/B) ratio was investigated as a function of Dy2O3 content. The simulation of a combination of a Blue LED (BL) emission with the sample emission was also studied in the CIE diagram, in order to evaluate the possibility of smart white light generation. Photoluminescence decay curves, fitted by Inokuti-Hirayama model (S = 6), indicates a dipole-dipole interaction between donor and acceptor Dy3+ ions in the glass. All results suggest that the investigated CaBAl:Dy3+ glasses are candidates for W-LEDs application and smart lighting.

Temperature-Dependent and Threshold Behavior of Sm3+ Ions on Fluorescence Properties of Lithium Niobate Single Crystals.

Temperature-dependent and threshold behavior of Sm3+ ions on fluorescence properties of lithium niobate (LiNbO3, LN) single crystals were systematically investigated. The test materials, congruent LiNbO3 single crystals (Sm:LN), with various concentrations of doped Sm3+ ions from 0.2 to 2.0 mol.%, were grown using the Czochralski technique. Absorption spectra were obtained at room temperature, and photoluminescence spectra were measured at various temperatures in the range from 73 K to 423 K. Judd–Ofelt theory was applied to calculate the intensity parameters Ωt (t = 2, 4, 6) for 1.0 mol.% Sm3+-doped LiNbO3, as well as the radiative transition rate, Ar, branching ratio, β, and radiative lifetime, τr, of the fluorescent 4G5/2 level. Under 409 nm laser excitation, the photoluminescence spectra of the visible fluorescence of Sm3+ mainly contains 568, 610, and 651 nm emission spectra, corresponding to the energy level transitions of 4G5/2→6H5/2, 4G5/2→6H7/2, and 4G5/2→6H9/2, respectively. The concentration of Sm3+ ions has great impact on the fluorescence intensity. The luminescence intensity of Sm (1.0 mol.%):LN is about ten times as against Sm (0.2 mol.%):LN at 610 nm. The intensity of the fluorescence spectra were found to be highly depend on temperature, as well as the concentration of Sm3+ ions in LiNbO3 single crystals, as predicted; however, the lifetime changed little with the temperature, indicating that the temperature has little effect on it, in Sm:LN single crystals. Sm:LN single crystals, with orange-red emission spectra, can be used as the active material in new light sources, fluorescent display devices, UV-sensors, and visible lasers.

Spectral properties of Nd3+ ions in the new fluoride glasses with small additives of the phosphates

A series of the new fluoride glasses with small additives of the phosphates doped with different of Nd3+ content is developed. The dopant concentration dependence of optical absorption and emission properties is reported here for the concentration range of 2.5×1020 to 1.0×1021 (ions/cm3). Using the Judd-Ofelt theory the phenomenological intensity parameters Ωt (t = 2; 4; 6) were obtained for all glasses studied. Fluorescence lifetime, quantum efficiency and nonlinear refractive index n2. were obtained. The peak stimulated emission cross sections of the transitions at 899 nm, 1053 nm and 1320 nm were calculated according to J-O theory. The stimulated emission cross-sections of 4F3/2→4I9/2,4F3/2→4I11/2 and 4F3/2→4I13/2 transitions were determined by the Fuchtbauer-Landenburg equation (FL) and the modified reciprocity method (MR) for all Nd3+concentrations. The analysis of the luminescence quenching depending on the concentration of the activator was carried out. It was concluded that present fluoride glass with small additives of phosphates is a promising material for laser applications.

Optical properties and radiative rates of Nd3+ doped zinc-sodium phosphate glasses

Preparation using melt quenching technique and optical characterizations of Nd3+ doped Zn-Na phosphate glasses are presented. The structure of the present glasses was studied using X-ray diffraction and FT-IR spectroscopy. UV-vis spectra of the present glasses were analyzed at different concentrations of Nd2O3. The effect of neodymium concentration on the density and energy band gap was investigated. The density of the present glasses slightly increases with the increasing of Nd2O3. A small variation of energy band gap with the increasing of neodymium content is observed as well, while Eg values decrease with the increase of Nd2O3 content. The Eg values lie between 4.36 and 4.69 eV. Based on the measured optical spectra, Judd-Ofelt theory was used to determine the optical parameters such as line strengths, optical intensity parameters (Ωt), transition probabilities, and transition lifetimes. Hypersensitive transitions were identified in the absorption spectrum, the greatest line strengths are recorded at the transitions 2G7/2 + 4G5/2, 4S3/2 + 4F7/2 and 4D1/2 + 4D3/2 + 4D5/2 + 2I11/2 with wavelengths of 580, 475 and 355 nm, respectively. Lifetimes of the important 4F3/2 laser-level were determined; which show decreasing trend with the increasing of Nd2O3 content and are found to be between 0.838 and 1.595 ms. The uncertainty of the present results was estimated. The RMS deviations were determined, which show lower values than those in the literature.

Investigation of Tm3+/Yb3+ co-doped germanate–tellurite glasses for efficient 2 µm mid-infrared laser materials

The Tm3+/Yb3+ co-doped germanate–tellurite glasses with good thermal properties were prepared. Based on the absorption spectra and the Judd–Ofelt theory, the J–O intensity parameters (Ω t ), radiative transition probability (276.78 s− 1), fluorescence lifetime (3.89 ms), absorption and emission cross sections ( $${\sigma _{\text{e}}}$$ = 1.35 × 10− 20 cm2) were calculated. The ~ 2 µm mid-infrared emission resulting from the 3F4→3H6 transition of Tm3+ sensitized by Yb3+ was observed pumped by 980 nm LD. Besides, the energy transfer mechanism between Yb3+ and Tm3+ was thoroughly discussed. The measured ~ 2 µm emission lifetime of Tm3+/Yb3+ co-doped glass can reach as high as 2.38 ms. The above results showed that Tm3+/Yb3+ co-doping glass could be expected to be a promising material to achieve high efficient ~ 2 µm lasing with a 980 nm LD pumping.

Spectroscopic properties of Nd:Gd0.89La0.1NbO4 mixed laser crystal

A Nd-doped niobate mixed laser crystal of Nd0.01:Gd0.89La0.1NbO4 (Nd:GLNO) has been grown successfully by Czochralski method. The absorption spectrum, fluorescence spectrum and fluorescence decay curve of Nd:GLNO crystal were measured at room temperature. The spectral parameters of Nd:GLNO crystal were obtained based on Judd-Ofelt (J-O) theory calculation. The three intensity parameters Ωt(t=2, 4, 6) were calculated to be 6.61, 1.43 and 3.31 × 10–20 cm2, respectively. On the base of the Ωt calculation, the branching ratios, spontaneous radiative probabilities, radiative lifetime and fluorescence quantum efficiency of the 4F3/2 level have been evaluated. Compared with other Nd-doped niobate laser crystal, Nd:GLNO shows a special spectral properties due to the large structure disorder caused by La3+. All the results demonstrate that this crystal is a specific low symmetrical laser material different from other niobates family crystals such as Nd:GdNbO4 (Nd:GNO) and Nd:YNbO4 (Nd:YNO) and can be considered as a promising laser material suitable for laser diode pumping.

Crystal growth and spectroscopic properties of Nd3+:(Ba0.32Sr0.68)5Nb4O15 crystal

Nd3+:(Ba0.32Sr0.68)5Nb4O15 crystal was grown by Czochralski method for the first time. The refractive indexes were measured. The polarized absorption and emission spectra were investigated at room temperature. The absorption cross-section and emission cross-section were presented. Based on Judd-Ofelt theory, the intensity parameters Ωt=2, 4, 6, radiative transition rates A, radiative lifetime τr and fluorescent branching ratio β have been obtained. The results show that Nd3+:(Ba0.32Sr0.68)5Nb4O15 crystal may be regarded as a potential solid-state laser gain medium material.

Structural and Optical Characteristics of Erbium Doped Ternary TeO<sub>2</sub>-TiO<sub>2</sub>-Bi<sub>2</sub>O<sub>3</sub> Glasses

In this work we investigated both structural and optical characteristic of erbium doped ternary TeO2-TiO2-Bi2O3 tellurite oxide based glasses, synthesized via melt-quench method. The X-ray diffraction (XRD) and differential scanning calorimetry (DSC) confirmed its glassy nature and stability. Raman analysis revealed the presence of various coordination state TeO2 network consisting stretching/bending vibrations of Te-O bonds in the [TeO4] trigonal bi-pyramid units and fraction of [TeO3, TeO3+1] trigonal pyramids. From optical absorption measurement both optical band gap and Judd-Ofelt analysis (intensity parameters Ωt(t=2, 4, 6), transition probabilities, and radiative lifetimes of the Er3+ ions) have been performed for both host and doped glasses respectively. Photoluminescence studies for upconversion and near-infrared emissions analysis (under 980 nm excitation at room temperature. Both optical transition mechanism which involved nonradiative energy transfer between Er3+ ions through cross-relaxation and energy migration were also explained in detailed.