Large Stimulated Emission Cross-section Research Articles

Suppression effect of auxiliary laser on stimulated Raman scattering effect of high-power Yb-doped fiber laser amplifier

<sec>A novel technique to suppress the stimulated Raman scattering (SRS) effect in high-power ytterbium-doped fiber amplifier is proposed and theoretically investigated by introducing an auxiliary laser to manipulate the gain distribution in the amplifier.</sec><sec>By injecting an auxiliary laser with shorter wavelength than the signal into the amplifier, the auxiliary laser, owing to its larger stimulated emission cross-section, initially extracts a significant portion of the laser gain. At this point, the gain of the longer-wavelength signal laser is suppressed to a certain extent. As the pump power is depleted in the rear segment of the gain fiber, the amplified auxiliary laser, which has larger absorption cross-section than the signal, is gradually absorbed by the active fiber and transfers its power to the signal laser. This process enhances the gain of the long-wavelength signal laser, enabling it to be rapidly amplified at the end of the amplifier. Compared with the amplification of the singular signal laser, the introduction of an extra auxiliary laser shifts the high-gain region of the signal laser to the rear portion of the amplifier, thereby reducing the effective length and alleviating the interaction strength between the signal laser and Stokes wave, in order to obtain a higher SRS threshold.</sec><sec>The SRS threshold of a 20 μm/400 μm fiber amplifier is investigated by using numerical simulation under different wavelengths of the auxiliary laser and different power ratios of the signal laser to auxiliary laser. The results indicate that incorporating an auxiliary laser with an appropriate wavelength and power level can significantly reduce the interaction strength between the signal and Stokes wave, thereby enhancing the SRS threshold of the amplifier efficiently. Specifically, in a 1080 nm fiber amplifier utilizing a 20 μm/400 μm ytterbium-doped large mode area fiber, if the total power of the 1080 nm signal and 1040 nm auxiliary laser is set to 200 W, while with a power ratio of 1:25, the SRS threshold increasing from 3.14 kW (singular signal laser) to 8.42 kW can be anticipated. Moreover, based on the auxiliary laser amplification technique that suppresses the SRS effect, the output power enhancement of fiber lasers with the structure of master oscillator power amplifier (MOPA) is also analyzed. This technical solution is relatively straightforward to implement and can be seamlessly integrated with other techniques aimed at reducing the SRS effect, which is promising to promote further power scaling of all-fiber amplifier.</sec>

A cyclic deep-red bis-squaraine molecular scaffold for improving random laser performance

A H-type cyclic bis-squaraine (bis-SQ) dye with deep-red emission is developed in this report to show enhanced random laser behaviors. Compared with the monomeric common squaraine dye (SQ), the rationally designed bis-SQ having cyclic interconnected dimeric squaraine architecture not only demonstrates about 20-32 nm bathochromic-shifts in the absorption and emission maxima, but also reveals significantly higher (∼4 times) fluorescence quantum yield and much longer (2-fold) fluorescent lifetime, which can be ascribed to the inhibition of internal energy loss and partial restriction of the intramolecular rotation in bis-SQ. The stimulated emission depletion (STED) microscopy and transient absorption spectra (TAS) studies of bis-SQ also confirms that it has much lower saturated excitation power (Psat) and saturated stimulated emission depletion power (Psted) in the range of 700–775 nm than conventional SQ, due to the larger stimulated emission cross section. The laser threshold of bis-SQ is also found to be markedly lowered than SQ which is about ∼20.8 μJ/cm2 for bis-SQ in comparison with ∼148.0 μJ/cm2 for SQ. This reduced laser threshold is instrumental in expediently implementing the bis-SQ dye as a random laser gain material in the deep-red region. Moreover, bis-SQ reveals excellent photostability and thermal stability which is essential for its potential application as a promising deep-red random laser gain material in future.

Exploration of Optical and Radiative Properties of Fluorinated β-keto Carboxylate Tb3+ Complexes Emanating Cool Green Light.

Tb3+ complexes with β-ketocarboxylic acid as main ligand and heterocyclic systems as auxiliary ligand were synthesized and analyzed to assess their prospective relevance as green light emitting material. The complexes were characterized via various spectroscopic techniques and were found to be stable up to ≈ 200 ℃. Photoluminescent (PL) investigation was performed to assess the emissive nature of complexes. Longest luminescence time of decay (1.34ms) and highest intrinsic quantum efficiency (63.05%) were fetched for complex T5. Color purity of complexes was found to be in range 97.1 - 99.8% which demonstrated the aptness of these complexes in green color display devices. NIR Absorption spectra were employed to evaluate Judd-Ofelt parameters to appraise the luminous performance and environment encircling Tb3+ ions. The JO parameters were found to follow the order: Ω2 > Ω4 > Ω6 and suggested the higher covalence character in complexes. Theoretical branching ratio in the range 65.32 - 72.68%, large stimulated emission cross section and narrow FWHM for 5D4 → 7F5 transition unlocked the relevance of these complexes as a green color laser media. Band gap and Urbach analysis were consummated via enforcing nonlinear curve fit function on absorption data. Two band gaps with values in between 2.02 - 2.93eV established the prospective use of complexes in photovoltaic devices. Energies of HOMO and LUMO were estimated employing geometrically optimized structures of complexes. Investigation of biological properties accomplished via antioxidant and antimicrobial assays which communicated their applicability in biomedical domain.

Telecom‐Wavelength Organic Single‐Crystal Lasers Triggered by the Molecular Conformation‐Dependent Cascaded Proton Transfer Processes

AbstractOrganic semiconductor molecules possess chemical tunability and large stimulated emission cross section, representing a promising candidate for laser gain medium. However, for the pursuit of telecom‐wavelength organic lasers, one of the major obstacles is the lack of effective energy‐level systems with high optical gain to compensate the exciton deactivation losses. Herein, the effects of molecular conformation‐dependent distinct cascaded proton‐transfer six‐level energy gain systems on lasing emission properties are systematically investigated based on organic polymorphs, proving that an energy‐level gain system without reversible transition channels is more conducive to the formation of efficient population inversion and high optical gain. Notably, the one‐way irreversible six‐level energy system of β‐phase polymorph supports more favorable population inversions than the two‐way reversible six‐level system of α‐phase polymorph due to the irreversible excited‐state second proton transfer and the irreversible ground‐state recovery, achieving the amplified spontaneous emission at telecom‐wavelength of ≈850 nm. This study provides useful guidelines for constructing efficient energy‐level gain systems, promoting the exploration of high‐gain organic semiconductor laser materials from visible to near‐infrared region.

Low threshold amplified spontaneous emission and lasing from single crystals and polymer microspheres based on a blue aggregation-enhanced emission molecule

Organic semiconductors as a gain medium have attracted much attention in organic lasers due to their unique properties, i.e., large stimulated emission cross section, widely tunable spectrum region, and mechanical flexibility. Aggregation-caused quenching broadly exists in amorphous solid films and single crystals, which result in high threshold. Here, we studied amplified spontaneous emission (ASE) and lasing properties of an aggregation-enhanced emission (AEE) molecule, namely, 2PB-AC, who owns high photoluminescence quantum efficiency in a solid film and a single crystal. The grown long rod-like single crystals exhibited very good ASE characteristics with a threshold of 48 μJ cm−2 and a full width at half-maximum (FWHM) of 8.4 nm. Furthermore, when forming polymer microspheres by a surface tension-induced self-assembly method, a low lasing threshold of 0.32 mJ cm−2 and a FWHM of 0.41 nm were also obtained well, and their lasing modes could be modulated by changing the diameter of the microspheres. The investigations on transient photoluminescence dynamics and femtosecond transient absorption analysis demonstrated that the high radiative decay rate and the well separation between a stimulated emission band and an excited state absorption band are the main reasons of good lasing performance, indicating that AEE molecules are promising lasing materials.

High-Performance Organic Laser Semiconductor Enabling Efficient Light-Emitting Transistors and Low-Threshold Microcavity Lasers.

An organic light-emitting transistor (OLET) is a candidate device architecture for developing electrically pumped organic solid-state lasers, but it remains a critical challenge because of the lack of organic semiconductors that simultaneously possess a high solid-state emission efficiency (Φs), a high and balanced ambipolar mobility (μh,e), and a large stimulated emission cross-section. Here, we designed a molecule of 4,4'-bis(2-dibenzothiophenyl-vinyl)-biphenyl (DBTVB) and prepared its ultrathin single-crystal microplates with herringbone packing arrangements, which achieve balanced mobilities of μh = 3.55 ± 0.5 and μe = 2.37 ± 0.5 cm2 V-1 s-1, a high Φs of 85 ± 3%, and striking low-threshold laser characteristics. Theoretical and experimental investigations reveal that a strong electronic coupling and a small reorganization energy ensure efficient charge transport; meanwhile, the exciton-vibration effect and negligible π-π orbital overlap give rise to highly emissive H-aggregates and facilitate laser emission. Furthermore, OLET-based DBTVB crystals offer an internal quantum efficiency approaching 100% and a record-high electroluminescence external quantum efficiency of 4.03%.

Photoluminescence and optical transition properties of Sm3+ activated lead-borate glasses

The Sm2O3-doped B2O3- K2O-PbF2 host glasses were synthesized by melt-quenching process. to comprehend visible luminescence and lasing potentiality, optical absorption, excitation, emission and decay measurement of developed glasses were studied. The experimental oscillator strength were calculated from absorption spectra of BKPFSm0.5 (optimized) glass sample. The decline in decay time as the proportion of samarium ions in the host glass increase indicates energy transfer between samarium ions. To establish potentiality of these glasses as visible lasers, the radiative properties of fluorescent transition acquired from photoluminescence emission spectra were determined. The quantum efficiency acquired from experimental and theoretical lifetimes was found to be 74% for the BKPFSm0.5 glass. The high quantum efficiency (η), large stimulated emission cross-section (σe = 6.49 × 10−22 cm2) and high branching ratios (βR = 59%) for 4G5/2 → 6H7/2 transition of the BKPFSm0.5 glass specify acceptability of this glass for improvement of lasing (orange) and the photonic devices emitting the in visible region.

Influence of ZnF2 and ZnCl2 on luminescence investigations and crystal field calculation of Eu3+ doped zinc oxide-phosphate glasses

A series of Eu3+-doped 70NaPO3–20ZnO-10(ZnF2/ZnCl2) glasses were prepared by conventional melting quenching method. The samples were characterized by differential scanning calorimetry (DSC), X-ray diffraction (XRD), electron probe microanalysis (EDS/WDS) and optical spectroscopy. Using the emission spectra a set of Judd-Ofelt (JO) intensity parameters (Ω2, Ω4, Ω6) was refined, which in turn permitted to calculate transition probabilities (AED, AMD), branching ratios (β), radiative lifetimes (τrad) and stimulated emission cross-sections for the 5D0-7FJ transitions. The relative luminescence intensity ratio of 5D0-7F2-5D0-7F1 transitions has been evaluated to estimate the local site symmetry around the Eu3+ ions. Second and fourth rank crystal-field (CF) parameters together with the CF strength parameter have been reported for the first time for such study by assuming the C2v symmetry for the Eu3+ ions in both the phosphate glasses. Large stimulated emission cross-section, high branching ratios and quantum efficiencies (∼80%), also, intense red luminescence at 616 nm confirm that these present glasses suggesting for visible red lasers materials and optical devices.

A Novel Strategy toward Thermally Activated Delayed Fluorescence from a Locally Excited State.

It is well-known that thermally activated delayed fluorescence (TADF) is always generated from charge-transfer (CT) excited states in donor-acceptor (D-A) systems, which limits its application owing to a slow radiative process and a small stimulated emission cross section. Herein, a design strategy is proposed for realizing TADF from a locally excited (LE) state without a typical donor-acceptor type structure through controlling the intersystem crossing (ISC) and reverse intersystem crossing (RISC) processes between the lowest excited singlet with LE character and higher triplet states. Using this strategy, a boron difluoride derivative is theoretically predicted and experimentally synthesized to exhibit locally excited TADF (LE-TADF) with a fairly large radiative rate of 1.12 × 108 s-1, extremely fast RISC rate of 5.09 × 1010 s-1, and a large stimulated emission cross section of 4.35 × 10-17 cm2, making this a promising organic amplified spontaneous emission (ASE) material. This work might open a new avenue to extend TADF materials, especially TADF laser emitters.

Pr3+-doped B2O3–Bi2O3–ZnO–NaF glasses comprising alkali/mixed alkali oxides for potential warm white light generation, blue laser, and E-+S-+C-optical bands amplification applications

For six 1 mol% Pr 3+ -doped B 2 O 3 –Bi 2 O 3 –ZnO–NaF glasses consisting of single and mixed alkali oxides, optical absorption and visible and near-infrared (NIR) luminescence traits including visible fluorescence decay times were investigated. Judd–Ofelt (J‒O) analysis from absorption spectra was performed to calculate J‒O parameters Ω λ ( λ = 2, 4, 6) by including and omitting 3 H 4 → 3 P 2 transition. Utilizing Ω 2 , Ω 4 , and Ω 6 values and refractive indices, radiative transition probabilities ( A R ), branching ratios ( β R ), and radiative lifetimes for all Pr 3+ ion's luminescent levels were estimated. For observed intense blue fluorescence band upon 443 nm optical pumping, various parameters considered in designing visible laser systems were evaluated. Pr 3+ : Na + K ions comprising glass possesses large spectroscopic quality factor, high A R and β R , large stimulated emission cross-section ( σ em ), high quantum efficiency, large gain bandwidth, and significant optical gain for 3 P 0 → 3 H 4 transition for a potential blue lasing action among all samples. Further, Commission Internationale de l'éclairage (CIE) coordinates, correlated color temperature (CCT), color rendering index, and luminous efficiency of radiation were derived from visible luminescence spectra and deduced CIE and CCT values represent the neutral or warm white light region. Upon 3 H 4 → 3 P 2 excitation, NIR luminescence spectra show 3 P 1 + 1 I 6 → 1 G 4 , 1 D 2 → 3 F 4 , and 1 D 2 → 1 G 4 transitions in which broadband ( 1 D 2 → 1 G 4 ) at 1.3–1.65 μm range with effective bandwidth ~157 nm was obtained for Pr 3+ : Na + K ions constituting glass with high A R (1938 s −1 ), moderate β R (26%), and large σ em (2.64 × 10 −20 cm 2 ) at 1.472 μm, and its gain profile covers the E-+S-+C-optical communication bands' range for effective broadband amplification operation.

Dy3+-doped Ga2S3-Sb2S3-La2S3 chalcogenide glass for mid-infrared fiber laser medium

We report a new Dy3+-doped Ga2S3-Sb2S3-La2S3 (GSLS) chalcogenide glass for mid-infrared (mid-IR) laser applications. With the addition of La2S3 into the previously studied Ga2S3-Sb2S3 glass, the thermal stability of the base glass is significantly enhanced. The glass with the composition 20Ga2S3-75Sb2S3-5La2S3 (mol.%) shows the best thermal stability for fiber drawing, and the glass can be doped with up to 5 mol.% Dy2S3. The Dy3+-doped GSLS bulk glasses and a multimode fiber exhibit intense emissions at 2.95 μm and 4.40 μm. Spectroscopic analyses show that the mid-IR emissions are with high quantum efficiencies and large stimulated emission cross sections, indicating that Dy3+-doped GSLS glass is a promising candidate for mid-IR fiber laser medium.

Mid-infrared luminescence of dysprosium-doped gallium-antimony-sulfur-iodine chalcohalide glasses and fibers

Dy3+ doped Ga-Sb-S-I chalcohalide glasses were prepared by melt-quenching method. The thermal stability and mid-infrared (MIR) luminescence of the glass samples were investigated systematically. Dy3+ dopants in Ga-Sb-S-I glasses exhibited intense 2.92-μm emission and 4.41-μm emission. High quantum efficiency and large stimulated emission cross section were observed for these two emission bands. Finally, Dy3+ doped Ga-Sb-S-I glass fibers were fabricated, using a core composition of 0.05 wt.% Dy3+: Ga8Sb32S55I5 and a cladding composition of Ga8Sb31S56I5. MIR attenuation and luminescence of the fibers were characterized. The fiber shows the minimum loss of 1.9 dB/m at 6 µm. Strong 3.0-µm and 4.4-µm emission bands were seen. It indicates that Dy3+ doped Ga-Sb-S-I glass fiber is promising for mid-infrared fiber gain medium usage.

~2 μm emission properties and energy transfer processes in Tm3+ doped Bi2O3-GeO2-Na2O glass laser material

Tm3+ doped Bi2O3-GeO2-Na2O glass samples were synthesized by conventional melt-quenching method. The Raman spectra measurements showed the maximum phonon energy of prepared glass is 794 cm−1, which is considerably lower than silicate glasses. Based on the measured absorption spectra, Judd-Ofelt intensity parameters, spontaneous radiative transition probabilities and radiative lifetimes were calculated to elucidate the radiative properties of Tm3+ in the presented glass. Intense near infrared emission around ~2 μm was obtained under the pump of 808 nm laser diode. A large stimulated emission cross section (5.51 × 10−21 cm2 at 1851 nm) of Tm3+: 3F4 → 3H6 was achieved in the prepared bismuth germanate glass doped with 1 mol% Tm2O3. Besides, the energy transfer processes among Tm3+ were analyzed using the extended overlap integral method. These results indicate that the presented glass is a promising candidate for ~2 μm laser applications.

Spectroscopic and luminescence properties of Ho3+ ions doped Barium Lead Alumino Fluoro Borate glasses for green laser applications

Optically transparent Barium Lead Alumino Fluoro Borate (BaPbAlFB) glasses doped with different concentrations of Ho3+ ions were prepared by using melt quench technique. Raman spectral studies were conducted to understand the structural groups present in the as prepared glasses at room temperature. Spectroscopic investigations such as optical absorption, excitation, emission and decay measurements were conducted to understand the visible photoluminescence (PL) and lasing potentialities of BaPbAlFB glasses. The bonding parameters (δ) estimated from the absorption spectral features were used to understand the nature of bonding between Ho3+ ions and the surrounding ligands. The Urbach energy values estimated from the absorption spectral data are used to verify the amorphous nature of the present glass system. The Judd-Ofelt (J-O) theory has been applied to the measured oscillator strengths of the absorption spectral features to estimate the best fit J-O parameters (Ωλ, λ = 2, 4, and 6) useful in evaluating various radiative parameters for the prominent fluorescent levels of Ho3+ ions in BaPbAlFB glasses. The experimental lifetimes (τexp) are found to be decreasing with increase in Ho3+ ion concentration owing to energy transfer. The quantum efficiency (η) of Ho3+ ions doped BaPbAlFB glasses were estimated by correlating the experimental lifetimes (τexp) with the radiative lifetimes (τR). The strong visible emission, large stimulated emission cross-section (σse), high branching ratio (βR) and relatively good quantum efficiency (η) obtained for 5S2→ 5I8 (green) transition of 1 mol% of Ho3+ ions doped BaPbAlFB glass reveals its suitability in designing and developing visible green lasers.

Europium-doped boro-telluro-dolomite glasses for red laser applications: Basic insight into spectroscopic traits

Naturally abundant minerals and lanthanide-doped synthetic boro-tellurite networks have become prospective efficient laser hosts because of the synergy between them. Driven by this idea, Eu3+-doped boro-telluro-dolomite (BTD) glasses were prepared via the melt-quenching method. The spectroscopic traits of as-quenched samples were analyzed though experimental and theoretical studies. The result from the derivation of absorption spectral fitting (DASF) model demonstrated the direct allowed transition in the glasses. Moreover, the photoluminescence spectra of the sample containing 1.0 mol% of Eu3+ (BTD1.0Eu glass) revealed a prominent red peak at 611 nm (assigned to 5D0 → 7F2 transition in Eu3+ ion) with a large stimulated emission cross section (7.15×10−22cm2) and a high luminescence branching ratio (61.5%). Furthermore, the attained CIE color coordinates (0.637, 0.363), which lie near the standard red hue (0.67, 0.33), together with high quantum efficiency (92.7%) affirmed the effectiveness of BTD1.0Eu glass as a potential red laser host.

Judd-Ofelt evaluation of europium ion transition enhancement in phosphate glass

Diverse application of inorganic glasses increases their demand, with this view, a new type of magnesium-zinc-sulfophosphate glasses were prepared with varied europium ions (Eu3+) doping (0 to 2.0 mol%). Such melt-quench synthesized glasses were characterized at room temperature to determine their physical and optical properties. XRD pattern of as-quenched samples confirmed their amorphous nature. Densities of glasses were increased (from 2.540 to 2.788 g.cm−3) with increase in Eu3+ doping contents. Absorption spectra disclosed eight significant peaks allocated. Photoluminescence (PL) spectra exhibited four characteristic peaks with emission intensity of the peak at 613 nm was highest. Emission peaks were enhanced with the rise in Eu3+ content up to 1.5 mol% and quenched thereafter. Values of Judd-Ofelt (J–O) intensity parameters Ω2 and Ω4 were ranged from 14.4 × 10-20 cm2 to 10.7 × 10-20 cm2 and 1.26 × 10-20 cm2 to 5.44 × 10-20 cm2, respectively. Branching ratio for 5D0→7F2 transition was ranged from 0.687 to 0.771 for Eu3+ content changed from 0 to 2.0 mol% and was higher than other transitions. The large stimulated emission cross-section suggested the prospect of glass composition for development of photonic devices and red laser.

Intense red and green luminescence from holmium activated zinc-sulfo-boro-phosphate glass: Judd-Ofelt evaluation

Rare-earth ions doped oxide glasses became prospective for high quality and inexpensive solid state laser development. To fulfill this need, zinc-sulfo-boro-phosphate glasses doped with holmium ions (Ho3+) were synthesized via melt-quenching method. Prepared glasses were characterized using diverse techniques to determine the influence of varied Ho3+ contents on their optical absorption and photoluminescence (PL) emission properties. The main purpose of this paper was to determine the structural and optical correlation in Ho3+ activated phosphate-based glass host involving the red and green lasing potency of holmium. Raman, XPS and FTIR spectra were recorded to analyze the structural properties of the synthesized glasses. Furthermore, Judd-Ofelt (J-O) intensity (Ωλ with λ = 2, 4 and 6) and radiative parameters were calculated. Absorption spectra of the studied glasses disclosed thirteen characteristic peaks associated to the transitions from the lowest electronic energy level (5I8) to various excited levels in Ho3+. The PL spectra of the proposed glasses revealed 3 significant peaks allocated to the 5F4 → 5I8, 5F5 → 5I8 and 5F4 → 5I7 transitions in Ho3+. Revelation of negative bonding parameter values implied the existence of ionic bond between the ligand and Ho3+ in the prepared glass host. Values of Ω2, Ω4 and Ω6 were observed in the range of (5.11–22.62)×10−20 cm2, (9.54–13.79)×10−20 cm2 and (3.71–6.78)×10−20 cm2, respectively. Lower Ω2 value signified the higher symmetry around Ho3+, whereas higher Ω4 and Ω6 values indicated the stronger rigidity of the glass network. The achieved large stimulated emission cross-section for the red and green spectral transitions from Ho3+ ((29.47–46.01)×10−21 cm2 for 5F4 → 5I8, (31.47–39.74)×10−21 cm2 for 5F5 → 5I8 and (13.34–31.63)×10−21 cm2 for 5F4 → 5I7) clearly displayed the lasing effectiveness of the proposed glasses.

Growth and spectroscopic characterization of Tm3+:Ca10Li(VO4)7 crystal-a potential crystalline medium for 2 µm lasers

The single crystal Tm3+:Ca10Li(VO4)7 with dimensions of Ø 23 × 25 mm3 was grown by Czochralski method. It’s thermal and spectroscopic properties were investigated. The thermal expansion coefficient αa is 1.671 × 10−5 K−1 and αc is 1.462 × 10−5 K−1. The absorption cross-sections at 794 nm are 2.43 × 10−20 cm2 and 1.04 × 10−20 cm2 for π- and σ- polarization, respectively. The largest stimulated emission cross-section corresponding to the 3F4 → 3H6 transition of Tm3+ ions, is 1.92 × 10−20 cm2 at 1883 nm for π- polarization and 1.69 × 10−20 cm2 at 1917 nm for σ- polarization. The fluorescence lifetime is 1.05 ms. The broad and smooth gain profile from 1750 nm to 2010 nm means that Tm3+:Ca10Li(VO4)7 is a potential laser crystal for tunable and ultrashort pulse lasers near 2 µm.

Synthesis, structure, Hirshfeld surface analysis and photophysical studies of red emitting europium acetylacetonate complex incorporating a phenanthroline derivative

Two new octa-coordinated red emitting complexes of the type [Ln(acac)3(Br2-phen)] [acac: acetylacetonate, Br2-phen: 4,7-dibromo-1,10-phenanthroline, Ln: Sm(III) and Eu(III)] have been synthesized and characterized. Single crystal X-ray diffraction (SCXD) of [Eu(acac)3(Br2-phen)] and [Eu(acac)3(H2O)2](H2O) revealed distorted square antiprism structure for both complexes. 2D fingerprint plots and Hirshfeld surface analyses signify important interactions in crystal packing [H⋯H (72.2%), O⋯H/H⋯O (18.9%) and C⋯H/H⋯C (6.7%) contacts for [Eu(acac)3(H2O)2](H2O), while [Eu(acac)3(Br2-phen)] showed H⋯H (40.5%), Br⋯H/H⋯Br (12.9%) and O⋯H/H⋯O (6.5%)] contacts]. Photophysical measurements gave quantum yield (QLnL) of 1.1 and 13% with corresponding luminescence lifetime (τobs) of 38.76 ± 0.61 μs and 790 ± 1.53 μs for [Sm(acac)3(Br2-phen)] and [Eu(acac)3(Br2-phen)], respectively. We have further evaluated photophysical properties of [Eu(acac)3(Br2-phen)] theoretically from the optimized sparkle structure and steady-state emission spectrum of Eu(III) complex. The intramolecular energy transfer (WET) and back-energy transfer (WBT) rate predicted from the calculated singlet (S1) and triplet (T1) levels to the emissive 5D1 and 5D0 states for Eu(III) follow the path S0 → S1 → T1 → 5D1 → 5D0 → 7F0,4. The Eu(III) complex showed large stimulated emission cross-section (σ(0→2) = 1.27 × 10−20 cm2) similar to Nd-glass laser (1.6–4.5 × 10−20 cm2) and offers promise for high-power laser medium.

Advances in Conjugated Polymer Lasers.

This paper provides a review of advances in conjugated polymer lasers. High photoluminescence efficiencies and large stimulated emission cross-sections coupled with wavelength tunability and low-cost manufacturing processes make conjugated polymers ideal laser gain materials. In recent years, conjugated polymer lasers have become an attractive research direction in the field of organic lasers and numerous breakthroughs based on conjugated polymer lasers have been made in the last decade. This paper summarizes the recent progress of the subject of laser processes employing conjugated polymers, with a focus on the photoluminescence principle and excitation radiation mechanism of conjugated polymers. Furthermore, the effect of conjugated polymer structures on the laser threshold is discussed. The most common polymer laser materials are also introduced in detail. Apart from photo-pumped conjugated polymer lasers, a direction for the future development of electro-pumped conjugated polymer lasers is proposed.