Stimulated Emission Cross-section Research Articles

Spectroscopy of thulium ions in solid-solution sesquioxide laser ceramics: Inhomogeneous spectral line broadening, crystal-field engineering and C3i sites

We present a detailed spectroscopic study of Tm3+ ions in stoichiometric and “mixed” (solid-solution) cubic (C-type, sp. gr. Ia3‾) sesquioxides R2O3 (RY, Lu, Sc or their mixture), with the goal of developing broadband-emitting gain media for ultrafast lasers at ∼2 μm. Evidence of a linear variation (increase) of the crystal-field strength when decreasing the ionic radius of the host-forming cation R3+ in the isostructrural R2O3 series is presented. The crystal-field splitting of Tm3+ multiplets is determined for C2 sites and justified using a barycenter plot, and the first evidence of C3i Tm3+ species is presented. A remarkable inhomogeneous spectral broadening for compositionally “mixed” sesquioxides (in particular with Sc3+) with respect to the parent compounds is revealed at low temperatures. It is proven that binary and ternary “mixed” R2O3 compounds form substitutional solid-solutions with a mixing of the host-forming cations at the atomic level. The stimulated-emission and gain cross-sections for the 3F4 → 3H6 Tm3+ transition are determined. Guidelines for material engineering of Tm3+-doped gain media for mode-locked 2-μm lasers are also provided.

Nd, Gd:SrF<sub>2</sub> crystal spectrum gain characteristic study on the broadband laser amplification

Spectral gain narrowing is one of the key factors affecting broadband amplification of ultrashort pulses. In this paper, the spectral gain characteristics in broadband amplification are studied theoretically and experimentally by using the characteristic of Nd,Gd:SrF<sub>2</sub> crystal, i.e. the emission spectrum has a certain width at the higher stimulated emission cross section. Through the numerical simulation, the evolution law of output spectrum of the laser gain medium under different spectral gain lineshapes and different gain values is studied in detail. Theoretical calculation shows that the spectral gain narrows obviously with the increase of gain values of the traditional Gaussian emission spectrum and increasing the spectral bandwidth at the maximum stimulated emission cross section can obviously suppress the spectral gain narrowing. Furthermore, the spectral gain narrowing characteristics of the Nd,Gd:SrF<sub>2</sub> crystal were studied experimentally. The Ф13mm×150mm Nd,Gd:SrF<sub>2</sub> crystal was used as the gain medium which was pumped by flash lamps in the experimental study. The experimental results show that the output spectra of Nd,Gd:SrF<sub>2</sub> crystals are not obviously narrowed when the input laser spectral width is 5nm (FWHM) and the gain is 140 times. The experimental results are consistent with the theoretical calculation and analysis. The crystal can work normally at the repetition rate of 0.2Hz and 1Hz in the experiment, but due to the influence of thermal effect, the gain will decrease to a certain extent with the increase of pump energy and repetition rate. The research results lay the foundation for the application of fluoride crystal in broadband chirped pulse amplification.

Achieving narrow bandwidth and high stimulated cross-section in Nd3+-doped LiCaB glasses for near infra-red laser amplifiers

The aim of this research is to examine the effects of Nd3+ ions on the spectroscopic characteristics of different concentrations of lithium-calcium-borate glasses and improve the emission cross section alongside bandwidth. The prepared glasses were produced with the melt-quenching technique and were thoroughly analyzed to determine their usefulness as laser amplifiers. Various studies were conducted, including X-ray diffraction (XRD), solid-state nuclear magnetic resonance (NMR), thermogravimetric analysis (TGA), absorption and emission measurements, and time decay curve measurements. The structural analysis using XRD and NMR techniques revealed that the glasses were amorphous and that non-bridging oxygen was present. Moreover, it was discovered that the glass-forming tendency and glass stability of these glasses improved with the concentration of Nd3+ ions. The glasses' absorption spectra display 10 transition states in UV and visible regions. Among all the prepared glasses, the lithium-calcium-borate glass doped with 0.5 mol % Nd3+ ions stand out with a stimulated emission cross-section value of 3.40 × 10−20 cm2 and a narrow bandwidth of 33 nm, making it an ideal lasing amplifier medium due to the 4F3/2 → 4I11/2 (1060 nm) transition. Theoretical Judd-Ofelt calculations were conducted to evaluate various parameters, including oscillatory strength, radiative parameters, radiative lifetime, gain bandwidth, figure-of-merit, and saturation current, for all transitions in the near-infrared region, to support the experimental investigations and offer a detailed discussion of these parameters.

Effect of mixed alkali ions on the structural and spectroscopic properties of Nd3+ doped silicate glasses

In the present work the effect of alkali ions (Li, Na, K) and the combination of them on structural and spectroscopic properties of Nd3+ doped silicate glasses were systematically investigated. Results from infrared and Raman spectroscopy, as well as density and refractive index, were used to investigate the effect on the structural properties of the silicate glasses. Absorption and emission spectra of the glass samples were measured in the UV-VIS and NIR ranges. Relatively large, stimulated emission cross-section at 1.06 μm was obtained for samples containing a combination of alkali ions, especially with potassium. Moreover, the splitting induced by the Stark effect on the hypersensitive transition of Nd3+,4I9/2 → 4G5/2, 2G7/2 was larger for the samples containing potassium, probably due to its larger ionic size. Judd-Ofelt theory was applied to evaluate the phenomenological intensity parameters Ω2, Ω4, Ω6, transition probabilities, radiative lifetimes and branching ratios related to Nd3+ ions, calculated from optical absorption and luminescence spectra and the results were compared to the values obtained for different Nd-doped glasses reported in the literature.

EFFECT OF PRASEODYMIUM ION CONCENTRATION ON OPTICAL AND LUMINESCENCE PROPERTIES OF TELLURITE GLASSES PRODUCED BY MELT-QUENCHING TECHNIQUE

Tellurite glasses with different concentration of praseodymium (Pr3+) ion was produced by melt-quenching technique. The effect of Pr3+ concentration on optical and luminescence properties was presented. The optical absorption spectra of Pr3+ ions in glasses were recorded in the UV-VIS-NIR region. By using the integrated absorption spectrum, the Judd-ofelt parameters for Pr3+ ions were derived. The Judd-Ofelt theory was used to calculate the radiative transition probability, stimulated emission cross-section, and branching ratio of the glasses. These findings support the use of these glasses in laser and other optical device applications.

Six-watt diode-pumped Tm:GdVO4 laser at 2.29 µm

A compact Tm:GdVO4 laser pumped by a 794 nm laser diode generated 6.09 W at 2.29 µm (3H4 → 3H5 Tm3+ transition) with a high slope efficiency of 30.8% and linear laser polarization (π). The polarized spectroscopic properties of Tm3+ in GdVO4 were also revised. The peak stimulated-emission cross section of Tm3+ is 2.97 × 10−20 cm2 at 2280 nm, corresponding to an emission bandwidth of 42 nm for π-polarized light.

Impact of modifiers on structural and optical properties of Dy3+doped different lithium tetraborate glasses for W-LED applications

The melt quenching technique achieved the synthesis of multiple samples of glasses were prepared, each containing Dy3+ ions as dopants and containing alkali and alkaline earth metals. Subsequently, several physical properties of these samples were assessed. The current investigation covers the characterization of Dy3+ doped lithium tetraborate glasses with varying compositions using powder X-Ray Diffraction (PXRD), FTIR, FT-Raman spectroscopy, optical absorption, and photoluminescence spectroscopy. The X-ray powder diffraction (PXRD) analysis indicates that the glass specimens exhibit an amorphous structure. The elemental composition of these materials has been determined using EDS. The utilization of FTIR and FT-RAMAN spectra is employed for the purpose of identifying distinct structural groups. J-O theory is employed to obtain J-O Intensity parameters and radiative parameters based on the absorption spectra. The photoluminescence spectra were utilized to determine the experimental branching ratios (βexp), effective bandwidths (Δʋeff), and stimulated emission cross-sections (σP) for all of the glass matrices that were prepared. The bi-exponential decay profiles of the 4F9/2 state were obtained and analyzed for all glass specimens containing Dy3+ ions. The lifetimes (τ) and quantum efficiencies (η) were determined by measuring decay profiles. Emission spectra are used to calculate correlated color temperatures (CCTs), CIE chromaticity coordinates and yellow-to-blue intensity ratios (Y/B).

Spectroscopic and Judd-Ofelt Analysis of Nd3+ Ion Doped Lithium Antimony-Borate Glasses for Visible and Near Infrared Laser Application Compared to Standard Emission at 1.06 μm

The present work focuses on the spectroscopic luminescence analysis of trivalent neodymium-doped lithium antimony-borate glasses, with the glass composition 70 Sb2O3—(25-x) B2O3–5 Li2O—x Nd2O3 where x = 0.3; 0.5; 0.7 mol% (SBLN). Around 475 nm excitation used by the transition 4I9/2 → 2G9/2 + 2D3/2 + 2K15/2 and that induced emission lines of wavelengths λ emis = 584;673;767;826 nm (red is low intensity). The specific emission follows the transitions 2G7/2 + 4G5/2 → 4IJ (J = 9/2; 11/2; 13/2; 15/2). Previous work on Nd3+ doped glasses studied near-infrared emission in 4F3/2 → 4IJ mode (J = 9/2; 11/2; 13/2) via near-infrared excitation 4I9/2 → 4F5/ 2+2H9/2. The Judd-Ofelt analysis applied to SBLN glasses showed that the ΩK parameters are consistent with the values in the literature. SBLN7 glass has the best spectroscopic factor Ω4/Ω6 = 0.974; while the best luminescence branching ratio is that of the green emission and it stands at an average β = 70%. Similarly, green emission has the best values of stimulated emission cross section and gain bandwidth. Calculated and measured lifetimes are ranged between 15 and 40 microseconds; however, quantum efficiency varies between 50 and 91%. In another side calculated and measured refractive index values are very close. The chromatic coordinates of observed green color showed accurately that lies in the yellowish-green region of the chromaticity diagram edited by CIE 1931. The calculation of its temperature was made by Mc Macy’s equation, and it is in the limits of 5100 K; which corresponds to a cool color similar to midday sunlight.

Studies of luminescence traits and Judd-Ofelt analysis of Sm3+ activated oxyfluoride glasses

Novel Sm3+ activated oxyfluoride glass was synthesized via the melt-quenching approach with subsequent heat treatment. The X-ray diffraction measurement discloses the amorphous nature of prepared glasses. And, FTIR illustrates the molar surplus of Bi2O3 raises the network connectivity by creating bridging oxygen sites in the structure. The Judd-Ofelt (J-O) intensity parameters exhibit Ω4>Ω2>Ω6 trend, witnessing the rigidity of the glass structure and ionic bonding between Sm3+ ions and surrounding ligands. The 4G5/2 → 6H7/2 transition of Sm3+ is the most applicable for reddish-orange lasers due to their higher values of radiative transition probability, branching ratio, and stimulated emission cross-section. The optimum emission intensity is obtained with 30 mol% Bi2O3 and the corresponding decay time is 1.40 ms. Additionally, the F30 glass sample was lit in a reddish-orange region having a CCT value of 1689 K. The thermal luminescence quenching of the prepared glass was studied and the thermal stability parameters activation energy was estimated. Further, the contactless optical thermometry capability of the glass sample was explored within the range of 303 K–603 K using the luminescence intensity ratio (LIR) technique. Thus, the above studies on the glass sample suggest that it can be used as an active medium in lasers, contactless optical temperature sensing, and high-energy scintillator applications.

Optical spectroscopy of the Er3+ ions in heavily doped BaY1.8Lu0.2F8:Er mixed crystals

Here we present the study of spectral and kinetic characteristics of Er3+ ions in the heavily doped BaY1.8Lu0.2F8 mixed crystals, which are homologous to well-known fluoride host BaY2F8 with high value of crystal field splitting.Absorption and luminescence spectra were registered, and the luminescence decay was studied in the IR spectral range for BaY1.8Lu0.2F8 crystals doped with Er3+ ions at concentrations of 20.0 at. % and 30.0 at. %. Based on the Judd-Ofelt theory, the intensity parameters were determined from the absorption spectra with the use of two approaches, the standard theory (J-O), and the intermediate configuration interaction (ICI). It is shown that investigated BaY1.8Lu0.2F8:Er3+ crystals propose the value of stimulated emission cross-section at the wavelength around 2.7 μm higher than that for Er-doped YAG and at the level of Er-doped LiYF4 crystals. In addition, it was shown that for BaY1.8Lu0.2F8 crystals with a high doping level of Er3+ (more than 20.0 at. %), the radiative lifetime of the 4I13/2 state becomes shorter than the lifetime of the 4I11/2 state, which speaks for success on efficient laser oscillation at a wavelength of about 2.7 μm (the 4I11/2 → 4I13/2 transition).

Sensitizing effect of Yb3+ ions on 1.53 µm broadband and 548nm upconversion green emissions of Er3+-doped TeO2–WO3–GeO2 glasses

The Er3+-doped transparent glasses were the significant materials to design solid state visible lasers, near infrared lasers, upconverters, sensors and fiber amplifiers. The effect of Yb3+ sensitization on 1.53 µm broadband and 548 nm upconversion green emissions in TeO2–WO3–GeO2–ErF3–YbF3 (TWGErYb) glasses were studied. They were characterized through structural, optical absorption, near infrared and upconversion studies. The Judd-Ofelt theory was adopted to estimate several spectroscopic and radiative parameters. The laser characteristic parameters such as stimulated emission cross sections, gain band widths, figure of merit and quantum efficiencies were evaluated. Conveying the energy from Yb3+ to Er3+ ions and the reasons for non-radiative losses were highlighted. The quenching in luminescence of 1.53 µm broadband, the 548 nm upconversion green emissions and the enhanced decay time values due to self-absorption were studied. The fitting of decay curves of Er3+: 4I13/2 and Er3+: 4S3/2 emission states at higher Yb3+concentrations (≥1.5 mol%) to Inokuti-Hirayama model were discussed. The TWGErYbx glasses containing 0.5Er3+/2.5Yb3+ show proficiency to design 548 nm green solid state lasers and 1.53 µm broadband fiber lasers.

Structural and spectroscopic studies of Er3+ in different fluorophosphate glasses for green laser and fibre amplifier operations

Erbium activated fluorophosphate glasses were synthesized with conceived characteristic combination, 59.5NH4H2PO4+15ZnO+15BaF2+10X+0.5Er2O3(X = LiF, NaF, CaF2, SrF2, AlF3) by melt quenching route. Based on the mass densities, and refractive indices, other physical properties i.e., dielectric constant (ε), reflection losses, molar refraction, internuclear distance and molar volume are determined. XRD has confirmed the non-crystalline character of the prepared glass samples. FTIR, FT-Raman have been employed to study the structural characteristics. Various radiative properties have been inferred through optical absorption measurements by standard Judd–Ofelt procedure. By excitation at 379 nm, all the glass hosts doped with constant concentration 0.5 mole% of Er3+have yielded intense green emission peak due to the transition 4S3/2 → 4I15/2 at 545 nm. Characteristic emission transition 4I13/2 → 4I15/2 at wavelength 1.53 μm has been studied extensively. Particularly the parameters related to that transition namely, stimulated emission cross-sections (σ e) and optical gains (G) are calculated from emission spectra. Among all the fluorophosphate glasses, the one which has shown higher σ e, and G values is sodium fluorophosphate (NFPE) glass. It is recommended for optical fiber amplification and NIR laser usage.

Luminescence properties of Dy3+ doped B2O3–CaMg(CO3)2 – TeO2 glasses: A promising host for solid state lighting devices

In this work, a novel series of 30B2O3–15CaMg(CO3)2–(55–x)TeO2–x Dy2O3(0.2≤x≥1.3 mol%) glasses coded as BDT x Dy are fabricated via conventional melt quenching procedure. The structure and luminescence properties of the as-produced glasses were explored through experimental and theoretical analyses. Through X-Ray profile, the amorphous status of the glasses was verified. FTIR spectra and N4 ratio analyses affirmed that Dy2O3 could act as a network modifier, transforming BO3→ BO4 and TeO3→ TeO4 units. Moreover, tthe characteristics of Dy3+ bond forming with O2−ion, oscillator strengths, band gap energies as well as Judd-Ofelt intensity units were deduced from the absorption spectra. Under 350 nm excitation wavelength, theemission spectra disclosed three f-f transitions situated around 482 nm, 575 nm and 662 nm attributed to 4F9/2→6H15/2, 6H13/2 and 6H11/2, respectively, wherein 4F9/2→6H11/2 transition, presentstrongest emission and better radiative properties. According to CIE 1931 chromaticity diagram, the current glasses radiate light, closer to the standard white light zone. To conclude, BDT x Dy glasses, due to their robust quantum efficiency (up to 97.97 %), boosted branching ratio (70 %) and remarkable stimulated emission cross section (≥ 10.15 × 10-22cm2) are promising for white light source and laser medium applications.

Growth, Structure, Spectroscopy, and Laser Operation of a “Mixed” Yb:(Y,Lu)3Al5O12 Garnet Crystal

A single crystal of ytterbium-doped “mixed” yttrium–lutetium aluminum garnet with a stoichiometric composition of (Y0.601Lu0.233Yb0.166)3Al5O12 was grown by the Czochralski method and its structure, vibronic, spectroscopic, and laser properties were studied. The stimulated-emission cross-section for Yb3+ ions was maximized to 2.53 × 10−20 cm2 at 1031 nm. The emission bandwidth was ~8 nm, and the reabsorption-free luminescence lifetime of the 2F5/2 state was 1.063 ms. Pumped at 941 nm, the Yb laser generated a maximum output power of 1.04 W at 1.03 and 1.05 μm with a high slope efficiency of 76.4% and a laser threshold of 76 mW. A continuous wavelength tuning over a range of 51.6 nm (1026.4–1078.0 nm) was also achieved. Power scaling was achieved using a 969 nm diode-pumped microchip cavity. A maximum output power of ~9 W was obtained at 1.05 μm with a slope efficiency of 76% and an almost circular laser beam profile.

Luminescence Behavior of Sm3+ Ion Doped Potassium Aluminium Gadolinium Phosphate Glasses as Orange Laser and Photonics Applications

Potassium aluminium gadolinium phosphate (KAGP) doped with difference contents of Sm3+ ion were synthesized by melt-quenching technique. The samples were further used to measure some physical, optical and luminescence properties. Absorption spectra show the hypersensitive transitions 6H5/2 → 6P3/2 and 6H5/2 → 6F7/2 at the wavelengths 402 and 1233 nm respectively. The photoluminescence spectra were recorded under 401 nm excitation, displayed the emission bands at 562, 597, 644 and 703 nm that corresponding to the transitions 4G5/2 → 6HJ (J = 5/2, 7/2, 9/2, 11/2) respectively, and the concentration quenching of Sm3+ showed at 1.0 mol%. Using the highest concentration of Sm3+ for emission spectra, Judd–Ofelt (J–O) analysis was performed to calculate the various radiative properties such as transition probabilities (AR), radiative lifetimes (τ R), branching ratios (β R) and stimulated emission cross-section (σ(λ p)) for different excited states. From the results of J–O parameter found to be Ω2 > Ω6 > Ω4 and the highest value of radiative properties was 4G5/2 → 6H7/2 transition. The decay curve for lower concentration was single exponential and became non-exponential for higher concentrations of the 4G5/2 level. According to the chromaticity coordinates (Commission Internationale de l′Eclairage), it indicated that the KAGP glass doped Sm3+ ion at 1.0 mol% lies in orange region. The KAGP glass doped concentration of Sm3+ at 1.0 mol% has potential application in developing the orange laser and suitable for optical device also.

White Light Emission and Judd-Ofelt Analysis of Dy3+ Doped Mixed Alkali Borate Glass for W-LEDs Material

The Dy3+ doped lithium sodium potassium borate glasses with white light-emitting were prepared by the melt quenching technique. In this work, optical, photoluminescence properties and Judd-Ofelt analysis of borate glasses have been investigated. For optical properties, Dy3+ doped glasses showed the absorption in visible and near-infrared region, which originate from 6H15/2 ground state to higher state. While the luminescence properties of Dy3+ doped glasses, the emission spectra were presented more intense at 484 nm (blue light) and 574 nm (yellow light) which are essential for white light emitting materials, whilst decay time decrease with an increase of Dy2O3 contents. The emission intensity of Dy3+ doped glasses were enhanced by adding Dy2O3 concentrations until 0.5 mol%, after that the emission intensities were decreased due to the concentration quenching effect. Judd-Ofelt is analyzed by using the absorption and photoluminescence results, The stimulated emission cross-section has been investigated in this work. The CIE 1931 chromaticity investigation shows that Dy3+ doped glass emitted light with white color. Hence, these glasses may be suitable candidates for use in W-LEDs material.

Optical characterization of Sm3+ doped phosphate glasses for potential orange laser applications

Undoped and Sm3+doped 45P2O5–45Na2O–2Al2O3–8BaO glasses were synthesized by the melt-quenching technique. The glass structure and luminescence properties were investigated by using Raman spectroscopy, scanning electron microscopy (SEM), spectroscopic ellipsometry, Judd-Ofelt theory and photoluminescence. Electron microscopy showed the homogeneity of samples. Raman spectroscopy revealed that the overall structure of the glass was unaffected by the doping of Sm3+ and ellipsometry was used to measure the optical constants. Judd-Ofelt (JO) analysis was performed on the absorption bands of Sm3+ (4f5) and the three phenomenological parameters (Ω2, Ω4, and Ω6) were computed and then used to determine radiative properties such as the radiative transition probability (Ar), the fluorescent branching ratio (βr), the stimulated emission cross-section (σe) and the radiative lifetime (τrad). Photoluminescence (PL) spectrum showed the typical four transitions of Sm3+ at wavelengths of 564, 600, 645 and 703 nm corresponding to 4G5/2 → 6H5/2, 6H7/2, 6H9/2 and 6H11/2, respectively. The spectroscopic quality factors Ω4/Ω6, the predicted lifetime (τrad) calculated using the JO method and the experimentally lifetime (τexp) for the 4G5/2 level were calculated and discussed. The glass color purity is as high as 98%, which makes it a potential candidate for laser emission.

Tailored spectroscopic characteristics of a new type of CuO nanoparticles-inserted borate glass system: Samarium concentration tuning effect

The demand for new glass hosts with emergent properties is constantly growing for various miniaturized applications. Thus, some new types of Sm2O3-activated strontium-telluro-alumino-magnesium-borate glasses with copper oxide nanoparticles (CuONps) insertion were made using melt-quenching approach. The obtained glasses were characterized to determine the effects of Sm2O3 concentration changes on their thermal, structural, and luminescence properties. XRD, FTIR, and HRTEM analyses of the samples verified their glassy nature, presence of different functional units and CuONps, respectively. DTA analysis showed excellent thermal stability of these glasses with a stability factor as much as 125 °C. The optical absorption properties of the glasses were highly sensitive to Sm3+ concentrations variation. The Judd-Ofelt intensity parameters of the glasses with and without CuONps followed the trend of Ω6˃Ω4˃Ω2 and Ω4˃Ω6˃Ω2, respectively. These glasses displayed 4 visible luminescence bands at 561, 598, 645, and 705 nm corresponding to 4G5/2 → 6H5/2, 4G5/2 → 6H7/2, 4G5/2 → 6H9/2, and 4G5/2 → 6H11/2 transitions in Sm3+. In addition, branching ratio above 80% and stimulated emission cross-section up to 135.82 × 10−23 cm2 were achieved. The stimulated emission cross-section and optical gain were enhanced due to the inclusion of CuONps in the glasses. These glasses may be useful for solid state laser and optical amplifier development.

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.

Spectroscopy of Yb3+,Ho3+,Eu3+-codoped calcium niobium gallium garnet (CNGG) crystal

Calcium niobium gallium garnet (CNGG) crystals codoped with Yb3+, Ho3+ and Eu3+ ions were grown by the Czochralski method. The crystal structure (cubic, sp. gr. O10h - Ia3d, lattice constant a = 12.4748(2) Å) was refined by the Rietveld method. A Raman study revealed high-energy vibrations at 767–846 cm−1 due to the [Nb2|Ga2O4] groups. The spectroscopic properties of Yb,Ho: and Yb,Ho,Eu:CNGG crystals were studied with the goal of developing broadband emitting gain media around 2 μm and 3 μm. The maximum stimulated-emission cross-sections σSE are 0.57 × 10−20 cm2 at 2070 nm (the 5I7 → 5I8 Ho3+ transition) and 1.01 × 10−20 cm2 at 2869 nm (the 5I6 → 5I7 Ho3+ transition) and the emission spectra are smooth and broad owing to the structural disorder of the CNGG host matrix. The evidence of Yb3+(2F5/2) → Ho3+(5I6) energy transfer (ET) in the Yb,Ho:CNGG crystal is shown. Without Eu3+, the luminescence lifetimes of the 5I6 and 5I7 Ho3+ states are 0.30 ms and 7.24 ms, respectively. The Eu3+ codoping leads to the quenching of the 5I7 Ho3+ lifetime due to the Ho3+(5I7) → Eu3+(7F6) ET which is favorable for 3 μm laser operation. The crystal-field splitting of the Ho3+ multiplets is revealed at 12 K. First laser operation in Yb,Ho:CNGG crystals at 2.1 μm is achieved.