TlCl Research Articles

Synthesis of porphyrin triads chelated with thallium(III) for studies of ground-state hole/electron transfer

Four target all-porphyrin triads have been prepared for fundamental studies of ground-state hole/electron transfer. Each triad contains thallium(III) porphyrins as bookends, which bear mesityl groups at the three non-linking meso-positions. The central porphyrin is a free base or thallium(III) porphyrin bearing mesityl or pentafluorophenyl groups at the two non-linking meso-positions. The linker is a 4,4′-diphenylethyne unit joined at the porphyrin meso-positions. The net spacer between the two bookend thallium(III) porphyrins thus consists of diphenylethyne–porphyrin–diphenylethyne and is designed as a superexchange element for through-bond hole/electron transfer. The energetics of the superexchange element are tunable given the nature of the substituents and metalation state of the central porphyrin. The synthesis entailed Sonogashira coupling of two building blocks, a free base bis(4-iodophenyl)porphyrin and a mono-ethynylporphinato thallium(III) chloride. Two benchmark porphyrins also were prepared. Absorption spectral comparisons are provided including of the all-thallium(III) monomer, dimer, and triad.

Crystal structure of hexa-chloro-thallate within a caesium chloride-phospho-tungstate lattice Cs9(TlCl6)(PW12O40)2·9CsCl.

Crystal formation of caesium thallium chloride phospho-tungstates, Cs9(TlCl6)(PW12O40)2·9CsCl showcases the ability to capture and crystallize octa-hedral complexes via the use of polyoxometalates (POMs). The large number of caesium chlorides allows for the POM [α-PW12O40]3- to arrange itself in a cubic close-packing lattice extended framework, in which the voids created enable the capture of the [TlCl6]3- complex.

Mechanisms of inclusion of thallium-201 into Prussian blue nanoparticles for nuclear medicine applications.

Prussian blue is known for its high affinity for thallium and other univalent metal cations and has been used as a treatment for radiocaesium and thallium/radiothallium poisoning. While Prussian blue nanoparticles (PBNPs) show potential for binding radioactive thallium for further use in nuclear medicine applications, the inclusion mechanism remains elusive. Understanding the interaction between PBNPs and 201Tl is essential for identifying the physicochemical and radiochemical properties required for optimal in vivo performance. In this work, we evaluated the binding mechanism between Tl and PBNPs with different coatings and core shapes. Combining PBNPs with [201Tl] thallium(I) chloride provided high radiolabelling yields and radiochemical stabilities under physiological conditions. Comprehensive characterisation by different X-ray techniques confirmed that Tl ions are located in the interstitial sites within the crystal structure, maintaining the integrity of the iron (Fe) 4p electronic distribution and inducing local modifications in the nearby C-N ligands. Additionally, this inclusion does not impact the core or the shell of the nanoparticles but does alter their ionic composition. The PB ionic network undergoes significant changes, with a substantial drop in K+ content, confirming that Tl+ ions replace K+ and occupy additional spaces within the crystal structure. These results open new opportunities in nuclear medicine applications with 201Tl-PBNPs where the size, shape and composition of the particles can be specifically tuned depending on the desired biological properties without affecting the radiochemical performance as a vehicle for 201Tl.

Double pseudo-polymeric complexes of [Au(S2CNR2)2][TlCl4], R2 = (CH2)5, (CH2)6: preparation, structural organization, and thermal behavior (low-temperature reduction and crystallization of gold)

The capability of thallium(I) alkylenedithiocarbamates to bind gold(III) from solutions in 2 M HCl was studied. Double complexes of [Au{S2CN(CH2)5}2][TlCl4] and [Au{S2CN(CH2)6}2][TlCl4] were preparatively isolated as individual forms of gold(III) binding into the solid phase. In the crystalline state, the ionic structural units of the complexes are combined together due to the secondary Au···S, Tl···S and S···Cl bonds that results in complicated supramolecular architectures. Thermal behavior of compounds was studied using the simultaneous thermal analysis technique; both reduced elemental gold and thallium(I) chloride were identified as the final thermolysis products.

In vitro and in vivo removal efficacy of insoluble Prussian blue in combination with calcium polystyrene sulfonate for thallium.

The similarities between thallium and potassium have suggested the use of calcium polystyrene sulfonate (CPS), an oral ion exchange resin, as a potential agent against thallium intoxication. Therefore, the study was an attempt to evaluate the efficacy of CPS and Prussian blue when given alone or in combination against thallium toxicity. The effect on binding capacity was investigated in terms of contact time, amount of CPS, influence of pH, simulated physiological solutions and interference of potassium ions. Also, rats were given single dose of thallium chloride (20mgkg-1) and the treatment with PB and CPS was given for 28days as CPS 30gkg-1, orally, twice a day, PB 3gkg-1, orally, twice a day and their combination. The effect of antidotal treatment was evaluated by calculating the thallium levels in various organs, blood, urine and feces. The results of the in vitro study indicated exceedingly quick binding in the combination of CPS and PB as compared to PB alone. Also, it was found that the binding capacity at pH 2.0 was considerably increased for PB with CPS (184.656mgg-1) as compared to PB (37.771mgg-1). Furthermore, statistically significant results were obtained in the in vivo study as after 7th day, thallium levels in blood of rats treated with combination were reduced by 64% as compared to control group and 52% as compared to alone PB treated group. Also, Tl retention in liver, kidney, stomach, colon and small intestine of combination treated rats was significantly reduced to 46%, 28%, 41%, 32% and 33% respectively, as compared to alone PB treated group. These findings demonstrate this as a good antidotal option against thallium intoxication.

Potential of Depth-of-Interaction-Based Detection Time Correction in Cherenkov Emitter Crystals for TOF-PET.

Cherenkov light can improve the timing resolution of Positron Emission Tomography (PET) radiation detectors, thanks to its prompt emission. Coincidence time resolutions (CTR) of ~30 ps were recently reported when using 3.2 mm-thick Cherenkov emitters. However, sufficient detection efficiency requires thicker crystals, causing the timing resolution to be degraded by the optical propagation inside the crystal. We report on depth-of-interaction (DOI) correction to mitigate the time-jitter due to the photon time spread in Cherenkov-based radiation detectors. We simulated the Cherenkov and scintillation light generation and propagation in 3 × 3 mm2 lead fluoride, lutetium oxyorthosilicate, bismuth germanate, thallium chloride, and thallium bromide. Crystal thicknesses varied from 9 to 18 mm with a 3-mm step. A DOI-based time correction showed a 2-to-2.5-fold reduction of the photon time spread across all materials and thicknesses. Results showed that highly refractive crystals, though producing more Cherenkov photons, were limited by an experimentally obtained high-cutoff wavelength and refractive index, restricting the propagation and extraction of Cherenkov photons mainly emitted at shorter wavelengths. Correcting the detection time using DOI information shows a high potential to mitigate the photon time spread. These simulations highlight the complexity of Cherenkov-based detectors and the competing factors in improving timing resolution.

NI-2 DUAL-ISOTOPE 123I-IMP/201TL SPECT FOR THE DIFFERENTIAL DIAGNOSIS OF PRIMARY CENTRAL NERVOUS SYSTEM LYMPHOMA AND GLIOBLASTOMA

Abstract Background Preoperative differential diagnosis between primary central nervous system lymphoma (PCNSL) and glioblastoma (GBM) is important because these tumors require different surgical strategies. This study investigated the usefulness of dual isotope, iodine-123-labeled N-isopropyl-p-iodoamphetamine (123I-IMP) and thallium-201 chloride single photon emission computed tomography (201Tl SPECT) for the differential diagnosis. Methods Sixteen PCNSL patients and 20 GBM patients who underwent dual isotope imaging, 123I-IMP and 201Tl SPECT, are included. Early and delayed SPECT images were obtained after 30 minutes and 4 hours, respectively. Tumor to normal (T/N) ratio was calculated from the ratio of maximum tracer counts in the lesion to the mean counts in the contralateral cerebral cortex. The mean and minimum apparent diffusion coefficient values (ADCmean and ADCmin, respectively) on magnetic resonance imaging were also analyzed for comparison of diagnostic accuracy. Results Delayed phase 123I-IMP SPECT was the most useful imaging examination for the differentiation between PCNSL and GBM compared with early phase 123I-IMP SPECT, early and delayed phase 201Tl SPECT, ADCmean and ADCmin. However, the median T/N ratios of PCNSL and GBM were 1.29 and 0.84, respectively, in the delayed phase 123I-IMP SPECT, and the tumor detection was inadequate. On the other hand, the median T/N ratios of PCNSL and GBM were 3.23 and 2.34, respectively, in the delayed phase 201Tl SPECT, with excellent tumor detection. Thirty-five of 36 patients (97.2%) showed a tracer retention rate of 201Tl SPECT 0.7 or higher, which indicates malignant property of brain tumors. Conclusion Delayed phase 123I-IMP SPECT could differentiate between PCNSL and GBM with high accuracy, but T/N ratio was low and tumor detection was poor. 201Tl SPECT was useful for estimation of the localization and the malignant property of the tumors. The combination of these isotopes was useful for the diagnosis of PCNSL and GBM.

Reassessing the potential of TlCl for laser cooling experiments via four-component correlated electronic structure calculations.

Following the interest in the experimental realization of laser cooling for thallium fluoride (TlF), determining the potential of thallium chloride (TlCl) as a candidate for laser cooling experiments has recently received attention from a theoretical perspective [Yuan et al., J. Chem. Phys. 149, 094306 (2018)]. From these ab initio electronic structure calculations, it appeared that the cooling process, which would proceed from transitions between a3Π0 + and X1Σ0 + states, had as a potential bottleneck the long lifetime (6.04 µs) of the excited state a3Π0 +, that would make it very difficult to experimentally control the slowing zone. In this work, we revisit the electronic structure of TlCl by employing four-component Multireference Configuration Interaction (MRCI) and Polarization Propagator (PP) calculations and investigate the effect of such approaches on the computed transition dipole moments between a3Π0 + and a3Π1 excited states of TlCl and TlF (the latter serving as a benchmark between theory and experiment). Whenever possible, MRCI and PP results have been cross-validated by four-component equation of motion coupled-cluster calculations. We find from these different correlated approaches that a coherent picture emerges in which the results of TlF are extremely close to the experimental values, whereas for TlCl the four-component calculations now predict a significantly shorter lifetime (between 109 and 175ns) for the a3Π0 + than prior estimates. As a consequence, TlCl would exhibit rather different, more favorable cooling dynamics. By numerically calculating the rate equation, we provide evidence that TlCl may have similar cooling capabilities to TlF. Our analysis also indicates the potential advantages of boosting stimulated radiation in optical cycles to improve cooling efficiency.

Usefulness of dual isotope 123I-IMP and 201Tl SPECT for the diagnosis of primary central nervous system lymphoma and glioblastoma.

Preoperative differential diagnosis between primary central nervous system lymphoma (PCNSL) and glioblastoma (GBM) is important because these tumors require different surgical strategies. This study investigated the usefulness of dual isotope, iodine-123-labeled N-isopropyl-p-iodo-amphetamine (123I-IMP) and thallium-201 chloride single-photon emission computed tomography (201Tl SPECT) for the differential diagnosis. Twenty-five PCNSL patients and 27 GBM patients who underwent dual isotope imaging, 123I-IMP and 201Tl SPECT, are included. Tumor-to-normal (T/N) ratio was calculated from the ratio of maximum tracer counts in the lesion to the mean counts in the contralateral cerebral cortex. The mean and minimum apparent diffusion coefficient values (ADCmean and ADCmin, respectively) on magnetic resonance imaging were also analyzed. Delayed phase 123I-IMP SPECT was the most useful imaging examination for the differentiation between PCNSL and GBM compared with early phase 123I-IMP SPECT, early and delayed phase 201Tl SPECT, ADCmean, and ADCmin. However, the median T/N ratios of PCNSL and GBM were 1.32 and 0.83, respectively, in the delayed phase 123I-IMP SPECT. On the other hand, the median T/N ratios of PCNSL and GBM were 3.10 and 2.34, respectively, in the delayed phase 201Tl SPECT, with excellent tumor detection. Delayed phase 123I-IMP SPECT could differentiate between PCNSL and GBM with high accuracy, but T/N ratio was low and tumor detection was poor. 201Tl SPECT was useful for estimation of the malignancy and localization of the tumors with high T/N ratio. Dual isotope 123I-IMP and 201Tl SPECT was useful for the preoperative diagnosis of PCNSL and GBM.

Time Resolution Studies of Thallium Based Cherenkov Semiconductors

In the context of improving the detector performance of time-of-flight positron emission tomography (TOF-PET), the combination of charge induction readout and prompt Cherenkov photon production in semiconductor materials can lead to an outstanding detector performance in energy, timing, and spatial resolution. Energy resolutions as good as 1.2% at 662 keV and 5% at 122 keV are reported for pixel thallium bromide (TlBr) detectors. The high refractive index of Tl-based materials, between 2.3 and 2.6, leads to a high Cherenkov photon generation yield but can also challenge photon extraction, potentially affecting the time performance. In this work, the timing properties of TlBr and thallium chloride (TlCl) crystals of different geometries are measured using an optimized test setup with high-frequency readout electronics. A coincidence time resolution (CTR) value of 167 ± 6 ps FWHM is achieved using a 3 × 3 × 3 mm3black-painted TlBr crystal. In order to assess potential improvements, a Geant4-based simulation tool kit is developed and validated against experimental measurements. The simulation tool kit is used to predict the contributions limiting the time resolution regarding the crystal and photodetector properties, highlighting the potential of such materials. Finally, paths to further improve the detector performance in TOF-PET are discussed.

Extraordinary intense blue Tl+ lone-pair photoluminescence from thallium(I) chloride hydroborate Tl3Cl[B12H12

Microcrystalline powder of previously unknown thallium(I) chloride hydroborate Tl3Cl[B12H12] was obtained through the reaction of thallium(I) oxocarbonate Tl2[CO3] with an aqueous solution of (H3O)2[B12H12] in the presence of chloride anions. Tl3Cl[B12H12] crystallises in a primitive, orthorhombic lattice with the space group Pnma (a = 835.189(7) pm, b = 970.132(8) pm and c = 1597.912(12) pm for Z = 4) showing a distorted hexagonal anti-perovskite type arrangement of the ions. The structure features two thallium sites with mixed coordination spheres consisting of borate related hydrogen atoms and chloride anions with coordination numbers of eleven and thirteen. Tl3Cl[B12H12] shows strong excitation bands at 240 and 260 nm attributed to the 1S0 → 3P2 and 1S0 → 3P1 interconfigurational transitions of the Tl+ 6s2 cations, respectively. The emission spectrum at 300 K upon VUV excitation exhibits a broad band at 440 nm with a quantum efficiency of 41%. In addition, temperature-dependent emission spectra, colour points, reflectance, decay time, thermal quenching curve and radioluminescence spectra for Tl3Cl[B12H12] were determined.

Study of Čerenkov Light Emission in the Semiconductors TlBr and TlCl for TOF-PET.

Thallium bromide (TlBr) and thallium chloride (TlCl) are semiconductor materials with high transparency to visible light, high index of refraction, and high detection efficiency for gamma rays and annihilation photons. This manuscript reports on measurements of the light intensity and timing response of Čerenkov light emitted in one 3 mm × 3 mm × 5 mm slab of each of these materials operated in coincidence with a lutetium fine silicate (LFS) crystal with dimensions of 3 mm × 3 mm × 20 mm. A 22Na radioactive source was used. The measured average number of detected photons per event was 1.5 photons for TlBr and 2.8 photons for TlCl when these materials were coupled to a silicon photomultiplier. Simulation predicts these results with an overestimation of 12%. The best coincidence time resolution (CTR) for events in TlBr and TlCl were 329 ± 9 ps and 316 ± 9 ps, respectively, when events with 4 photons and >7 photons were selected. Simulation showed the CTR degraded from 120 ps to 405 ps in TlCl, and from 160 ps to 700 ps in TlBr when the first or second Čerenkov photon were selected. Results of this work show TlCl has a stronger Čerenkov light emission compared to TlBr and a greater potential to obtain the best timing measurements. Results also stress the importance of improving detection efficiency and transport of light to capture the first Čerenkov photon in timing measurements.

Radiation Exposure of Medical Staff Conducting Stress Myocardial Perfusion Imaging.

Background: The myocardial perfusion stress conducted by physicians and nurses requires two imaging sessions, one during stress and the other during rest. Echocardiography is sometimes performed before delayed imaging, and medical laboratory technicians (MLTs) have similar exposure in such cases. This study was designed to investigate the radiation exposure of physicians, nurses, radiologists, and MLTs involved in thallium-201 chloride (201TlCl) stress myocardial perfusion imaging and echocardiography, the details of which have not been reported to date. Methods: The dose rate at thallium-201 (201Tl) was examined using a cylindrical phantom. The exposure of physicians, nurses, and radiologists involved in the 201TlCl stress myocardial perfusion imaging was measured using pocket dosimeters, and that of the MLTs in charge of echocardiography were measured using glass-batch dosimeters. Results: The attenuation of radiation exposure from the phantom with distance was 95% at 50 cm from the center of the phantom, demonstrated that the attenuation of the exposure dose increased with distance. The exposure dose for physicians, nurses, and radiological technologists that participated in 201TlCl stress myocardial perfusion imaging was 0.20-0.23 μSv per exam, whereas it was 6.67-10.00 μSv per exam for MLTs. Conclusion: This study measured the dose received by physicians, nurses, and radiological technologists during stress MPI and the dose received by MLTs during echocardiography. The results provided advanced knowledge for the management of dose received by medical personnel.

Optical and Electrical Analyses of Thallium Sulphide Thin Films

Abstract: In this paper, suitability of thallium sulphide films were investigated as an alternative to conventional silicon and germanium that were used as window layers in solar cells. Thin films were deposited on soda lime glass (SLG) substrates in a chemical bath containing Thallium Chloride (TlCl2) and Thiourea (NH2)2CS which was conditioned at 80 ºC for about 5 hours to deposit the films. Effects of annealing on the film samples at 300 ºC and 350 ºC were studied respectively by use of UV-VIS Avantes electrophotometer and Four-Point-Probe (FPP) machine in the light region with wavelength range from 200 nm to 1000 nm. The results obtained suggest that the thin films obtained are good materials for optoelectronics. The absorption spectra exhibited a relatively high energy band-gap. Materials of this nature are good for window layers which serve as passage to the absorber layer where needed charge carriers are produced. Keywords: Thin film, Thallium Sulphide, Window layer, Optoelectronics, Solar cells.

ЭКСТРАКЦИЯ ХЛОРИДНЫХ И ТИОЦИАНАТНЫХ АЦИДОКОМПЛЕКСОВ МЕТАЛЛОВ В СИСТЕМАХ ВЫСАЛИВАТЕЛЬ – МОНОАЛКИЛПОЛИЭТИЛЕНГЛИКОЛЬ – ВОДА

Distribution of iron (III), thallium (III, gallium, titanium (IV) chloride complexes in sodium chloride – synthanol DS-10 – water and ammonium sulfate – synthanol DS-10 – water systems, as well as iron (III), cobalt , nickel, cadmium and copper (II) thiocyanate complexes in the ammonium sulfate – synthanol DS-10 – water system investigated. It was found that the main influence on extraction is exerted by solution acidity and nature of the salting-out agent. The conditions for quantitative extraction of thallium (III) and gallium in the form of chloride complexes, as well as the conditions for maximum extraction of iron (III), zinc and cobalt thiocyanate complexes are established.

Scanning transmission imaging in the helium ion microscope using a microchannel plate with a delay line detector.

A detection system based on a microchannel plate with a delay line readout structure has been developed to perform scanning transmission ion microscopy (STIM) in the helium ion microscope (HIM). This system is an improvement over other existing approaches since it combines the information of the scanning beam position on the sample with the position (scattering angle) and time of the transmission events. Various imaging modes, such as bright field and dark field or the direct image of the transmitted signal, can be created by post-processing the collected STIM data. Furthermore, the detector has high spatial and temporal resolution, is sensitive to both ions and neutral particles over a wide energy range, and shows robustness against ion beam-induced damage. A special in-vacuum movable support gives the possibility of moving the detector vertically, placing the detector closer to the sample for the detection of high-angle scattering events, or moving it down to increase the angular resolution and distance for time-of-flight measurements. With this new system, we show composition-dependent contrast for amorphous materials and the contrast difference between small-angle and high-angle scattering signals. We also detect channeling-related contrast on polycrystalline silicon, thallium chloride nanocrystals, and single-crystalline silicon by comparing the signal transmitted at different directions for the same data set.

Accuracy of washout rate analysis for thallium-201 single-photon emission computed tomography myocardial perfusion imaging using cadmium zinc telluride detectors: A phantom study.

ObjectiveThe aim of this study was to assess the accuracy of washout rate (WOR) analysis for thallium-201 chloride (201Tl) single-photon emission computed tomography myocardial perfusion imaging data acquired using cadmium zinc telluride detectors and a myocardial phantom.MethodsA myocardial phantom was injected with 10.5 MBq 201Tl, and 10-min acquisitions were performed at 0, 24, 46, and 62 h to accommodate natural radioactive decay over time. Global myocardial WOR (global-WOR) and regional WOR (regional-WOR, left anterior descending artery [LAD], right coronary artery [RCA], and left circumflex artery [LCX]) were analyzed between 0 and 24 h (infarction model), 0 and 46 h (ischemia model), and 0 and 62 h (normal model), respectively. We compared the calculated radioactive decay-rate as a reference standard and phantom imaging WOR (phantom-WOR).ResultsDecay-rate versus phantom-WOR were 20.4% vs. 20.8% (global-WOR), 21.3% (LAD), 21.2% (RCA), and 19.7% (LCX) for the infarction model; 35.4% vs. 35.6% (global-WOR), 35.5% (LAD), 36.2% (RCA), and 35.2% (LCX) for the ischemia model; and 44.5% vs. 45.1% (global-WOR), 45.4% (LAD), 44.7% (RCA), and 43.5% (LCX) for the normal model.ConclusionWOR analysis for 201Tl single-photon emission computed tomography myocardial perfusion imaging using cadmium zinc telluride detectors is a reliable analysis method.

Evaluating the effectiveness of a single CT method for attenuation correction in stress-rest myocardial perfusion imaging with thallium-201 chloride SPECT.

This study aimed to evaluate the effectiveness of a single computed tomography (CT) based attenuation correction method using thallium-201 chloride (201TlCl) in stress-rest myocardial perfusion imaging (MPI). The data of 106 patients who underwent MPI with single photon emission computed tomography (SPECT) using 201TlCl were retrospectively reviewed. MPI SPECT images were reconstructed using stress SPECT and stress CT (SIO), rest SPECT and rest CT (RIO), and rest SPECT and stress CT (RIA). The accuracy of alignment between the SPECT and CT images was evaluated with normalized cross-correlation (NCC) and visual examination. The summed rest score (SRS) was used to evaluate hypoperfusion at rest; washout rate (WO) was used to assess ischemia; and left ventricular ejection fraction (LVEF) was used to evaluate the left ventricle (LV) function. There was no significant difference in NCC and visual evaluation in all three dimensions. The SRS of both RIO and RIA (7.5 ± 7.7 and 7.7 ± 7.6, respectively) did not differ significantly. However, SRSs of RIO and RIA showed a strong correlation (r = 0.98). The WO was 39.0 ± 0.98% for both RIO and RIA, with a strong correlation between the two values (r = 1.00). LVEF was 61.1 ± 17.4% for RIO and 61.3 ± 17.4% for RIA, and a strong correlation was observed between the two values (r = 1.00). In conclusion, the single CT-based attenuation correction method with 201TlCl SPECT has an accuracy equivalent to that of the conventional two CT-based attenuation correction method.

Kinetics of Thallium Dissolution in Aqueous Solutions of Hydrochloric Acid

Potentiometry is used to study the kinetics of electrochemical oxidation and reduction of thallium in aqueous solutions of hydrochloric acid. Kinetic parameters are calculated to characterize the mechanism of the electro-oxidation of thallium: coefficient of diffusion D, heterogeneous rate constant ks of the electrode process, and effective activation energy Eeff. The effect the modes of electrolysis (current density, electrolyte concentration, and temperature) have on the dimensional characteristics of the obtained thallium(I) chloride is studied. The optimum parameters of electrolysis for preparing dispersed powders of thallium(I) chloride are revealed.

Laser cooling of thallium chloride: A theoretical investigation.

The possibility of laser cooling of thallium chloride (TlCl) molecules has been investigated based on high-level ab initio calculations with the consideration of the core-valence and the spin-orbit coupling (SOC) effects. The potential energy curves of the 13 Λ-S states as well as the 24 Ω states split from them via SOC are obtained by multi-reference configuration interaction plus the Davidson correction. We show that the a transition of TlCl is a possible candidate for laser cooling, which features highly diagonal Franck-Condon factors and no intermediate interacting electronic states. Based on our calculations, we propose an optical cycling scheme by utilizing four lasers at wavelengths around 320 nm with more than 104 cycles for photon absorption/emission and a sub-microkelvin temperature limit.