Temperature Gradient Technique Research Articles

Dynamic high‐temperature crystallization and processing properties of industrial soda–lime–silica glasses

AbstractIn situ dynamic crystallization properties of industrial soda–lime–silica glasses at realistic processing temperatures have not yet been explored. Hence, we collected in situ high‐temperature X‐ray diffraction patterns for 10 different industrially manufactured soda–lime–silica glasses as a function of temperature between 900 and 1200°C to investigate the phase relations in their devitrified melts. The high‐temperature X‐ray diffraction study was complemented by measuring the liquidus temperature of those glasses by the temperature gradient technique. A multiple variable regression analysis was applied to the experimental and modeled data to produce a predictive model for the rate of solidification and liquidus temperature based on glass composition. We have demonstrated that forms of quartz (SiO2) and Na2CaSiO4, which are not traditionally identified by room temperature X‐ray diffraction studies of commercial soda–lime–silica glasses, are the dominant crystalline phases at 800 and 900°C. Upon further heating, different forms of cristobalite become the primary phase field prior to the formation of X‐ray amorphous melts, irrespective of the glass composition. Sporadic unidentified as well as high‐temperature stable SiO2 polymorphs that are not recoverable to room temperature were also observed. In contrast to the literature, wollastonite (CaSiO3) and devitrite (Na2Ca3Si6O16), which are the main predictor variables in previously developed liquidus temperature models, were not observed prior to the formation of X‐ray amorphous glass melts, and hence their influence on liquidus temperature may be questionable. It was also found that the difference between glass processing and liquidus temperatures can be excessively high, and such large temperature differences can potentially be exploited and reduced to enable decreases in melting or processing temperatures of industrial soda–lime–silica glass melts.

Effects of temperature on factors relevant to laser operation near 1.6 µm wavelength in resonantly (in-band) pumped CaF2:Er and SrF2:Er crystals: a comparative study

Single crystals of CaF2 and SrF2 containing Er3+ ions with concentrations between 0.01 and 0.6 at% respectively, were grown using the temperature gradient technique (TGT). Absorption spectra related to the 4I15/2 → 4I13/2 transition of Er3+ ions were measured at 5 K to investigate the properties of the crystal field splitting of the 4I13/2 multiplet, and at several temperatures in the region 80 K – 300 K to determine the effect of temperature on the spectral bands. The 4I13/2 → 4I15/2 luminescence spectra were recorded within the same temperature range as for absorption measurement. The analysis of absorption and luminescence spectra provides an in-depth knowledge on the effect of temperature on the factors that govern the efficiency of resonant optical pumping near 1.6 µm and the resulting lasing ability of Er3+ ions imbedded in CaF2 and SrF2 hosts.

Atmospheric Boundary Layer Height: Inter-Comparison of Different Estimation Approaches Using the Raman Lidar as Benchmark

This work stems from the idea of improving the capability to measure the atmospheric boundary layer height (ABLH) in variable or unstable weather conditions or in the presence of turbulence and precipitation events. A new approach based on the use of rotational and roto-vibrational Raman lidar signals is considered and tested. The traditional gradient approach based on the elastic signals at wavelength 532 nm is also considered. Lidar data collected by the University of Basilicata Raman lidar (BASIL) within the Special Observation Period 1 (SOP 1) in Cardillargues (Ceveninnes–CV supersite) during the Hydrological Cycle in the Mediterranean Experiment (HyMeX) were used. Our attention was specifically focused on the data collected during the period 16–21 October 2012. ABLH estimates from the Raman lidar were compared against other innovative methods, such as the recently established Morphological Image Processing Approach (MIPA) and the temperature gradient technique applied to potential temperature obtained from radio-sounding data. For each considered methodology, a statistical analysis was carried out. In general, the results from the different methodologies are in good agreement. Some deviations have been observed in correspondence with quite unstable weather conditions.

∼2.9 μm continuous-wavelength laser operation of fiber-pumped Ho,Pr:CaF2 single crystals

Ho,Pr:CaF2 single crystals were grown by modified temperature gradient technique method (TGT). A systematic study on the fluorescence characteristics around 2.9 μm has been carried out on this kind of materials for the first time, to the best of our knowledge. After co-doping with Pr3+, the population inversion is much easier to realize and the ratio of populations between the upper and lower energy levels is highest among the reported materials, which shows the Ho,Pr co-doped CaF2 is a kind of promising materials. The continuous-wavelength (CW) laser operation has been achieved with the maximum output power of 154 mW on 1%Ho,0.1%Pr:CaF2 crystals. It's the first report about the CW laser output on Ho-doped CaF2 single crystals.

Enhance and modulated near-infrared luminescence of Tm3+:CaF2 crystal by co-doping Y3+ ions

A series of 0.5 at.% Tm:Ca1-xYxF2+x (x = 0, 0.01, 0.04, 0.06, 0.08, 0.12) crystals have been successfully grown by the temperature gradient technique (TGT) method. The absorption spectra, fluorescence spectra, and fluorescence decay curves were measured and analyzed at room temperature. By comparison, it is found that when the concentration of Y3+ ions reaches 8 at.%, the absorption cross section corresponding to the 3H6→3H4 energy level is 2.56 × 10−21 cm2 at 793 nm, which is suitable for GaAlAs LD pumping. The J-O strength parameters Ω2, Ω4, and Ω6 were obtained. With the incorporation of Y3+ ions, the value of Ω4/Ω6 gradually increases. When the concentration of Y3+ ions reaches 8 at.%, the emission cross sections are 3.05 × 10−21 cm2 at 1476 nm, 2.56 × 10−21 cm2 at 2378 nm, and the full widths at half maximum (FWHM) are 76 nm and 195 nm, respectively. The fluorescence lifetime of 3H4 level, the upper level of 1.5 μm and 2.3 μm, is 1.05 ms, which is very beneficial for 1.5 μm and 2.3 μm laser.

Enhanced blue and broadband near-infrared emission of Pr3+/Yb3+ co-doped PbF2 single crystal

High quality Pr3+ single-doped PbF2 and Pr3+/Yb3+ co-doped PbF2 single crystals were grown by temperature gradient technique (TGT). By co-doping Yb3+ ion as Pr3+ ions sensitizer, the visible light emission can be regulated and the largest luminescence branching ratio can be switched from red-orange to blue-green light. Besides, when Pr3+ ions doping concentration is as low as possible, the blue light self-absorption effect can be weakened, which is beneficial to high-efficiency blue laser output. Moreover, the broad band emission around 1.3 μm from 1G4 energy level can be observed in the Pr3+/Yb3+:PbF2 crystal with the low maximum phonon energy for the first time. Absorption, emission spectra and luminescence mechanism are well analyzed by the energy transfer process and J-O theory. The laser upper energy level lifetime of Pr3+ ions has a great increase by Yb3+ ion effect. These advantageous spectroscopic characteristics show that the Pr3+/Yb3+:PbF2 crystal might be potential laser gain materials for blue-green and ∼1.3 μm near-IR laser operation.

Growth and spectroscopic properties of CaxSr1-xF2: Sm: Gd single crystals

Eight single crystals of CaxSr1-xF2: Sm, Gd solid state solutions were grown by modified temperature gradient technique. Their spectroscopic properties were studied at 300 K and 77 K. The absorption spectra at room and LN2 temperatures suggest that there are more types of clusters in CaF2 rather than SrF2 samples (when the Sm3+ concentration is kept below 0.1 at.%). The addition of Gd3+ does not alter Sm2+/Sm3+ ratio significantly. Co-doping of samples with Gd3+ lead to significant changes in absorption and, emission and luminescence kinetic characteristics of Sm3+ ions. Changes in luminescent properties are due to creation of SmxGdyFz clusters. Presence of Clusters can also be confirmed by effective Energy Transfer from Gd3+ to Sm3+ ions.

Effect of Yb[formula omitted] concentration on Er[formula omitted] doped CaF[formula omitted] single crystal for temperature sensor applications

Yb–Er co-doped CaF2 crystals with different Yb3+ ions concentrations are successfully grown by the temperature gradient technique (TGT) method. Up-conversion (UC) luminescence characteristics and optical temperature sensing behavior of all samples are thoroughly investigated in this work. Under the excitation of a 980 nm laser-diode, the up-conversion luminescence intensity firstly increases and then decreases. By adjusting the content of Yb3+ ions, multi-color visible light emissions of red, yellow and green could be easily obtained. The fluorescence intensity ratio from two thermally coupled 2H11/2 and 4S3/2 levels technology is used to evaluate the temperature sensing performance of Yb–Er co-doped CaF2 crystals. The concentration of Yb3+ ions shows a significant influence on the temperature sensing performance. The sensitivity reaches the maximum value of 2.24 × 10−3 K−1 at 548 K with a 5 at.% doping concentration of Yb3+ ions. The experiment also confirms that Yb–Er co-doped CaF2 crystal exhibit high stability as optical temperature sensors. In general, it is proved that Yb–Er​ co-doped CaF2 single crystals are a kind of promising materials used in the optical temperature sensor.

Enhanced 1.5 μm emission of Tm3+ via Pr3+ deactivation in PbF2 crystal

Tm3+ doped and Tm3+,Pr3+ co-doped PbF2 single crystals with high quality were grown by Temperature Gradient Technique (TGT). The absorption spectra, fluorescence spectra, and lifetimes were investigated at room temperature. The absorption transition of Tm3+:3H6→3H4 matches well with the pumping source of the AlGaAs laser diode. The 1.5 μm emission intensity originating from Tm3+: 3H4→3F4 transition was enhanced significantly by co-doping Pr3+ ions. The energy transfer efficiency from the Tm3+: 3F4 level to the Pr3+: 3F2 level is as high as 90.2%, indicating that the Pr3+ ion is an effective deactivate ion for enhancing the ∼1.5 μm emission in Tm,Pr:PbF2 crystal. The results indicated that Tm,Pr:PbF2 crystal would be the promising candidate for 1.5 μm laser output.

Laser-diode-pumped Tm:SrF2 single crystal for high efficiency CW laser operation at ∼2 µm.

A Tm:SrF2 single crystal is grown by a modified temperature gradient technique (TGT). A study of the fluorescence characteristics and laser performance is carried out. Under laser-diode (LD) end-pumping, a continuous-wave (CW) laser is demonstrated. A slope efficiency of up to 81.8% is first achieved in the Tm-doped single crystals, which is extremely close to the photon quantum efficiency of 2.00. Such a high photon quantum efficiency is caused by the effective cross-relaxation process between Tm3+ ions. A maximum output power of 4.082 W is also obtained. The laser performance indicates that Tm:SrF2 is a promising candidate for highly efficient ∼2 µm lasers.

Tb,Y:SrF2 crystal for efficient laser operation in the visible spectral region.

A Tb,Y:SrF2 crystal with high optical quality is grown using the temperature gradient technique. The spectroscopic and laser properties of the crystal in the visible spectral region are studied. A fluorescence lifetime of 5.6 ms is measured from the crystal, which is beneficial for laser operation with a low threshold. A continuous-wave Tb,Y:SrF2 laser delivers an output power of 259 mW at 545 nm, with a slope efficiency of 35.2%. To the best of the authors' knowledge, this is the first report on a Tb-doped SrF2 laser and represents the highest output power for visible alkaline-earth fluoride lasers. The limitations for power scaling are discussed.

Influence of Na+, Ca2+ and R3+ (R = Y, Lu, Gd) co-doping on the spectroscopic properties of Pr3+:BaF2 single crystal

A series of high quality x%Pr3+:BaF2 (x = 0.6, 1, 2); (1%Pr3+, 2%Na+):BaF2; (1%Pr3+, y%Ca2+):BaF2 (y = 3, 5) and (0.6%Pr3+, 10%R3+):BaF2 (R = Y, Lu, Gd) crystals were grown via a temperature gradient technique (TGT).

Enhanced and modulated visible luminescence of Pr3+:CaF2 crystal by co-doping R3+ (R=Y, Gd, Lu) ions

A series of 0.6 at% Pr:CaF2-RF3 (R = Y3+, Gd3+, Lu3+) crystals have been successfully grown by the temperature gradient technique(TGT). The absorption spectra, fluorescence spectra, and fluorescence decay curves were measured and analyzed at room temperature. When the R3+ concentration is higher than a certain value, the diffraction peaks of Pr:CaF2-RF3 crystals were well indexed to the (Ca,Y)F2 phase. By co-doping R3+ ion (R=Y3+, Gd3+, Lu3+), the spectral performance of the crystals could be significantly improved and the function effect is also different. For 0.6 at% Pr, 28.5 at% Y:CaF2 crystal, the fluorescence lifetime of 3P0 energy level was fitted to be 45.46 µs, and the emission cross sections of 3P0→3H6 (605 nm), and 3P0→3F2 (641 nm) were calculated to be 1.78 × 10−20 cm2, and 4.61 × 10−20 cm2 with the full width at half (FWHM) of 20.1 nm and 6.8 nm, respectively. The 0.6 at% Pr, 28.5 at% Y:CaF2 crystal could be favorble laser medium for ultra-fast laser opreration at 605 nm and 641 nm. For 0.6 at% Pr, 18 at% Gd:CaF2 and 0.6 at% Pr, 10 at% Lu:CaF2 crystals, the spectral quality factors σem•τf of 3P0→3F2 transition (642 nm) were calculated to be 614.18 × 10−20 cm2•µs and 506.36 × 10−20 cm2•µs with the FWHM of 3.7 nm and 5.3 nm. All the results show that 0.6 at% Pr, 18 at% Gd:CaF2 and 0.6 at% Pr, 10 at% Lu:CaF2 crystals are promising gain media for high-efficiency visible laser output at 642 nm, which would compete with commercial Pr: YLF crystal in the future.

Crystal growth, spectral properties and Judd–Ofelt analysis of Pr: CaF2-YF3 * *Project supported by the National Natural Science Foundation of China (Grant Nos. 61805177, 61861136007, and 61621001).

The 0.6 at.% Pr3+-doped CaF2-YF3 crystal was successfully grown by the temperature gradient technique (TGT). X-ray diffraction analysis showed that the grown crystal still had cubic structure. The absorption spectrum, emission spectrum, Judd–Ofelt analysis and fluorescence decay curve at room temperature were discussed. The fluorescence lifetime of Pr: CaF2-YF3 crystal was 45.46 μs, and the σ em ⋅ τ of 3P0 → 3H6 and 3P0 → 3F2 transitions were calculated to be 80.92 × 10−20 cm2 ⋅ μs and 388.7 × 10−20 cm2 ⋅ μs, respectively. The FWHMs are 20.1 nm and 6.8 nm, which are higher than those of Pr: LiYF4, Pr: LiLuF4, Pr: LiGdF4 and Pr: BaY2F8 crystals. The results show that the Pr: CaF2-YF3 crystal is expected to achieve 605 nm orange light and 642 nm red light laser operation.

Effects of composition and phase relations on mechanical properties and crystallization of silicate glasses

AbstractCrystallization, mechanical properties, and workability are all important for the commercialization and optimization of silicate glass compositions. However, the inter‐relations of these properties as a function of glass composition have received little investigation. Soda‐lime‐silica glasses with Na2O‐MgO‐CaO‐Al2O3‐SiO2 compositions relevant to commercial glass manufacture were experimentally studied and multiple liquidus temperature and viscosity models were used to complement the experimental results. Liquidus temperatures of the fabricated glasses were measured by the temperature gradient technique, and Rietveld refinements were applied to X‐Ray powder diffraction (XRD) data for devitrified glasses, enabling quantitative determination of the crystalline and amorphous fractions and the nature of the crystals. Structural properties were investigated by Raman spectroscopy. Acoustic echography, micro‐Vicker's indentation, and single‐edge‐notched bend testing methods were used to measure Young's moduli, hardness, and fracture toughness, respectively. It is shown that it is possible to design lower‐melting soda‐lime‐silica glass compositions without compromising their mechanical and crystallization properties. Unlike Young's modulus, brittleness is highly responsive to the composition in soda‐lime‐silica glasses, and notably low brittleness values can be obtained in glasses with compositions in the wollastonite primary phase field: an effect that is more pronounced in the silica primary phase field. The measured bulk crystal fractions of the glasses subjected to devitrification at the lowest possible industrial conditioning temperatures indicate that soda‐lime‐silica glass melts can be conditioned close to their liquidus temperatures within the compositional ranges of the primary phase fields of cristobalite, wollastonite, or their combinations.

TGT growth and magneto-optical properties of PrF3 crystal

High quality PrF3 crystal was successfully grown by the temperature gradient technique (TGT). The magneto-optical properties of PrF3 crystal were systematically investigated in the UV-VIS-NIR region. The advantage of PrF3 over CeF3 and TGG is its transparency in deep-UV region down to 258 nm. The dispersions of Verdet constant of PrF3 and TGG crystals in VIS-NIR region are similar. The Verdet constant of PrF3 crystal can theoretically increase from 677.93 rad T−1•m−1 at 300 nm to 967.53 rad T−1•m−1 at 270 nm. The CeF3 and TGG crystals aren't transparent in this region. Therefore, PrF3 crystal is the promising candidate for use as a Faraday rotator for optical systems operating below 300 nm.

Bi-doped GaTe single crystals: Growth and thermoelectric properties

Here bismuth (Bi) was utilized to substitute Te sites to increase the hole concentration, thereby enhancing the thermoelectric performance of GaTe. Bi-doped GaTe single crystals have successfully been fabricated by a temperature gradient technique. Bi atoms acting as acceptors helped to increase hole concentration from 9.43 × 1015 ​cm-3 for pristine GaTe to 0.63, 0.90, 1.20, and 1.63 × 1017 ​cm-3 for BGT-1, BGT-2, BGT-3, and BGT-4 single crystals, respectively. Moreover, the carrier mobility was increased up to 68.25 ​cm2 ​V-1 ​s-1 due to the crystallinity improvement of GaTe. Consequently, the electrical conductivity and power factor (PF) reached the respective maximum values of 3.62 ​S ​cm-1 and 1.21 ​μW ​cm-1 ​K-2 at 500 ​K for BGT-4 crystals. Meanwhile, Bi doping less affected the thermal transport properties of GaTe single crystals. A peak zT of ~0.02 was achieved at 700 ​K for the BGT-4 sample.

Br-Doped n-Type SnSe2: Single-Crystal Growth and Thermoelectric Properties

In this work, pure, large Br-doped SnSe2 single crystals were successfully synthesized using the temperature gradient technique. Br acts as a donor, resulting in electron concentrations up to ∼6.83...

Growth and thermal stability studies of layered GaTe single crystals in inert atmospheres

In this study, we investigated the thermal stability properties in inert atmospheres of GaTe single crystals fabricated by a temperature gradient technique. The obtained crystals possess a monoclinic layered structure with high crystalline quality. To explore the thermal stability of GaTe, the differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were performed up to 1173 ​K in N2 and Ar atmospheres. GaTe crystals are thermally stable up to 700 ​K in Ar and stable up to 935 ​K in N2 due to the protective role of the physically adsorbed N2 molecules on GaTe surface. Annealing effect on the structural and optical properties of GaTe were examined after thermal treatment in N2 atmosphere at different temperatures; 573, 673, 773, and 873 ​K. Three prominent Raman modes at 97 ​cm−1 (Ag), 145 ​cm−1 (Ag), and 158 ​cm−1 (Bg) corresponding to the monoclinic GaTe phase almost remained, suggesting no structural damage at elevated temperatures. Especially, the photoluminescence (PL) intensity is improved as the annealing temperature increases and reaches a maximum at 673 ​K owing to the enhancement in the GaTe crystallinity. Above 873 ​K, we observed a significant reduction in the PL intensity, which is attributed to the vacancies induced by tellurium evaporation.

Growth, spectroscopic properties and up-conversion of Yb, Pr co-doped CaF2 crystals

Yb,Pr:CaF2 crystals have been grown successfully by the temperature gradient technique(TGT). The absorption spectra, fluorescence spectra, fluorescence decay lifetime of Pr3+ ions in CaF2 crystal sensitized by different Yb3+ ions concentration have been measured. The effective J-O intensity parameters were fitted to be Ω2=0.36 × 10−20cm2, Ω4=2.89 × 10−20cm2, Ω6=6.69 × 10−20cm2 for 0.3 at.%Pr,1.5 at.%Yb:CaF2. And the emission cross sections of 3P1→3H5 (535 nm), and 3P0→3F4 (750 nm) are calculated to be 2.02 × 10−20cm2, and 2.50 × 10−20cm2 with the FWHM of 17.2 nm, and 10.5 nm, respectively. The fluorescence lifetime of 3P0 has achieved great increasing by sensitizing of Yb3+ ion. Not only the up-conversion luminescence can be achieved, but also the broad band emission from 1D2 energy level can be observed. The results show that Yb,Pr:CaF2 could be a potential laser gain medium for visible and near-IR laser operation.