Induced Color Change Research Articles

Comparative Analysis of Modern 3D-Printed Hybrid Resin-Ceramic Materials for Indirect Restorations: An In Vitro Study

The study investigated the impact of aging on surface roughness, color stability, and biocompatibility of hybrid resin-ceramic materials. A total of 225 specimens were produced from three three-dimensional (3D)-printed (HarzLabs Dental Sand Pro (HL), BEGO VarseoSmile Crown plus (BV), Voco V-Print c&b temp (VV)) and one milled material (Voco Grandio Blocs (VG)). Specimens were grouped into untreated, polished, and glazed surfaces. 5000 thermal cycles simulated aging. Surface roughness and color stability were analyzed, and surface topography was observed using scanning electron microscopy (SEM). Biocompatibility was evaluated with L929 cells. Surface roughness differed significantly between untreated and other groups, with no changes before and after artificial aging. Untreated milled samples were significantly smoother than 3D-printed ones. SEM analysis revealed roughest surfaces in untreated 3D-printed specimens. Polished and glazed specimens were smoother than untreated ones. Color values showed significant differences between untreated and treated/aged groups. No material showed cytotoxicity. In summary, untreated VG was smoother than 3D-printed materials, but polishing and glazing reduced roughness to levels comparable to VG. Surface treatments induced color changes, with glazing causing more changes than polishing. Aging affected color stability and biocompatibility but not surface roughness. All materials showed acceptable color changes and good biocompatibility.

Improvement of Hygienic and Phytochemical Qualities of Mangosteen (Garcinia Mangostana) Peel by Irradiation

The aim of this study was to compare the effects of gamma ray and x-ray irradiation at different dose levels 95, 10, 15 and 20 kGy) on in mangosteen peel. The antioxidant activities were assessed using 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric reducing antioxidant power (FRAP), while total phenolic contents and antibacterial activities against Staphylococcus aureus and Escherichia coli of 60 % ethanolic mangosteen powder extracts were analyzed. The results indicated that both types of ionizing radiations showed a non-significant decrease in measured parameters with increasing doses. The minimum inhibitory concentration (MIC) values of irradiated mangosteen peel extracted against S. aureus and E. coli ranged from 0.125 to 2.0 mg/mL. The quantity of bioactive compound mangostin determined via high-performance liquid chromatography (HPLC), did not show significant decrease with different irradiation sources and doses. In microbiological aspect, total yeast and mold from both irradiation sources were reduced by 1 log cycle after irradiation at 5 kGy. The irradiation induced color changes corresponding to Hunter color L a b value. X-ray irradiation caused slight color alteration compared to gamma rays. The advantage of x-ray irradiation was that it revealed non-significant changes in b values, whereas gamma irradiation showed the significant change in L, and b values with increasing dosage. The x-ray irradiation at the dose 5 kGy effectively decreased microbial contamination while causing minimal changes to phytochemical qualities and color. HIGHLIGHTS Irradiation at 5 kGy was sufficient to control microbial contamination There were no significant changes in antioxidant activities (DPPH, FRAP), a-mangostin contents, total phenolic contents (TPC) and antibacterial activities: after irradiation up to 20 kGy X-ray irradiation was an excellent alternative to gamma irradiation for decontamination with a non-significant alteration in b values. GRAPHICAL ABSTRACT

Heating revival of Cs3MnBr5 for anti-counterfeiting and large-area flexible X-ray imaging

Cesium manganese bromide metal halide has great potential in the field of X-ray imaging and anti-counterfeiting due to its excellent optoelectronic properties. Here, Cs3MnBr5 was successfully prepared by a simple method. Uniquely a novel phenomenon based on H2O induced color change was discovered, Cs3MnBr5 can recover from aqueous solution more than 10 times under heating, which can be used in fluorescent anti-counterfeiting applications. Furthermore, Cs3MnBr5@PDMS, prepared by the PDMS composite strategy, has been demonstrated to exhibit a stability that is 20 times greater than that of Cs3MnBr5. Simultaneously, the light yield of Cs3MnBr5 is evaluated to be 21688 photons/MeV. Furthermore, it has been successfully applied in non-destructive detection and biological imaging and the spatial resolution can be restored to 10 lp mm−1.

Mechanisms for electric field induced color change in coupled colloidal quantum dot molecules revealed by low temperatures single particle spectroscopy

Mechanisms for electric field induced color change in coupled colloidal quantum dot molecules revealed by low temperatures single particle spectroscopy

An intelligent myofibrillar protein film for monitoring fish freshness by recognizing differences in anthocyanin (Lycium ruthenicum)-induced color change

A novel smart film MP/BNC/ACN for real-time monitoring of fish freshness was developed using myofibrillar protein (MP) and bacterial nanocellulose (BNC) as film raw materials and anthocyanin (Lycium ruthenicum, ACN) as an indicator. Firstly, the film containing 1 % ACN (MP/BNC/ACN1) was found to have a moderate thickness (0.44 ± 0.01 mm) and superior mechanical properties (tensile strength (TS) = 8.53 ± 0.11 MPa; elongation at break (EB) = 24.85 ± 1.38 %) by determining the physical structure. The covalent, electrostatic, and hydrogen bonding interactions between anthocyanin and the film matrix were identified and confirmed by FT-IR spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscope (SEM) analysis. A comprehensive evaluation concluded that MP/BNC/ACN1 exhibited excellent trimethylamine (TMA) sensitivity (total color difference (ΔE), ΔETMA0-1000 = 4.47–31.05; limit of detection (LOD), LOD = 1.03) and UV stability (ΔE96h = 4.16 ± 0.13). The performance of the films in assessing fish freshness was evaluated, principal component analysis (PCA) and hierarchical cluster analysis (HCA) revealed that MP/BNC/ACN1 (ΔE2-10d = 16.84–32.05) could clearly distinguish between fresh (0–2 d), sub-fresh (4–6 d), and spoiled (8–10 d) stages of fish, which corresponded to the film colors of red, light red, and gray-black. In conclusion, this study addresses the limitation that intelligent films cannot visually discern real-time freshness during fish storage and provides a promising approach for real-time fish freshness monitoring.

The physical and cellular mechanism of structural color change in zebrafish

Many animals exhibit remarkable colors that are produced by the constructive interference of light reflected from arrays of intracellular guanine crystals. These animals can fine-tune their crystal-based structural colors to communicate with each other, regulate body temperature, and create camouflage. While it is known that these changes in color are caused by changes in the angle of the crystal arrays relative to incident light, the cellular machinery that drives color change is not understood. Here, using a combination of 3D focused ion beam scanning electron microscopy (FIB-SEM), micro-focused X-ray diffraction, superresolution fluorescence light microscopy, and pharmacological perturbations, we characterized the dynamics and 3D cellular reorganization of crystal arrays within zebrafish iridophores during norepinephrine (NE)-induced color change. We found that color change results from a coordinated 20° tilting of the intracellular crystals, which alters both crystal packing and the angle at which impinging light hits the crystals. Importantly, addition of the dynein inhibitor dynapyrazole-a completely blocked this NE-induced red shift by hindering crystal dynamics upon NE addition. FIB-SEM and microtubule organizing center (MTOC) mapping showed that microtubules arise from two MTOCs located near the poles of the iridophore and run parallel to, and in between, individual crystals. This suggests that dynein drives crystal angle change in response to NE by binding to the limiting membrane surrounding individual crystals and walking toward microtubule minus ends. Finally, we found that intracellular cAMP regulates the color change process. Together, our results provide mechanistic insight into the cellular machinery that drives structural color change.

Raman spectroscopy of thermo- and laser-induced transformations of gouache paint layer of copper phthalocyanine blue

Methods to control polymorphic modifications of phthalocyanines using optical (laser) radiation and possible photoinduced transformations of polymorphs are of practical interest in problems of identification and attribution of paintings, laser (micro)sampling, and the development of phthalocyanine structures for technical applications in optics, optoelectronics, and medicine. In this work, we compare the thermal and laser-induced changes of a gouache paint layer based on copper phthalocyanine (CuPc) PB15. The thermally induced color changes of the paint layer are quantified using the CIE Lab D65/10 color space. (Nano)rods formed in the paint layer when the sample is heated to 450°C at normal pressure without humidity control are studied using absorption spectroscopy, Raman microspectroscopy, and scanning electron microscopy. It is shown that the formation of (nano)rods is related to the α→β polymorph transition of CuPc. Low-frequency markers of the CuPc β-polymorph are revealed in the Raman spectra. For the sample containing (nano)rods, the a* color coordinate substantially increases (by about 30 units), whereas the L* and b* coordinates remain almost unchanged. Irradiation with a single nanosecond laser pulse at a wavelength of 532 nm leads to the laser ablation of the paint layer at fluences exceeding a threshold level of about 3 J/cm2. Irradiation at fluences of greater than 0.5 J/cm2, but lower than the ablation threshold leads to color change of the paint layer due to the α→ε transition of CuPc. Similar transformations are observed at the periphery of and inside ablation crater.

Chemometric analysis illuminates the relationship among browning, polyphenol degradation, Maillard reaction and flavor variation of 5 jujube fruits during air-impingement jet drying

This study was designed to reveal the relationship among browning, polyphenol degradation, Maillard reaction (MR) and flavor variation in jujube fruit (JF) during air-impingement jet drying (AIJD). Five kinds of JFs were dried by AIJD at 60 °C and vacuum freeze drying. Colorimeter and chemometric analysis found that AIJD induced color changes of JF pulp and peel. AIJD also reduced the total polyphenols content and total flavonoids levels in JF. The Fe3+ reducing capacity and 2,2′-Azinobis-(3-ethylbenzothiazoline-6-sulphonate) cationic radical scavenging capacity of JF were reduced by 31.6% and 8.2%, respectively. Seven polyphenols were identified in JF, and epicatechin was found related to change of JF pulp color by sparse partial least square (sPLS). sPLS revealed that 3-deoxy glucosone, N-ε-carboxymethyl-l-lysine and 5-hydroxymethylfurfural associated with JF color. sPLS found that MR generated 3-methyl-butanoic acid and cyclobutanone during AIJD of JF. Chemometrics is an effective tool to disclose mechanism of color changes in food.

Evaluation of the color stability of three maxillofacial silicone materials after exposure to beverages: An in vitro study

PurposeOral cancer often requires treatments like surgical intervention, involving surgical resection of lips and other facial parts. For those patients, prosthetic rehabilitation following surgery promotes social reintegration. This study explores the color stability of various commercially available silicone materials for facial prostheses when exposed to everyday beverages like coffee and tea. The hypothesis is that these beverages can induce color changes in silicones, simulating conditions of daily use. Material and methodsA total of 90 specimens were fabricated. There were 30 specimens deefor each of 3 nonpigmented silicone elastomers: Silfy, A-2186-F and VST-50 and were immersed in tea or coffee at drinking temperature and evaluated for color changes at time points of 0 h, 1 h, and 6 h. The color was measured with a colorimeter that used the CIE L*a*b* system and the color change ΔΕ was calculated to quantify the color change. Statistical analysis was performed by using the Kruskal-Wallis test, the Mann-Whitney U test, and the Wilcoxon signed-rank Test. The threshold for statistical significance was P < .05. ResultsColor change was observed for each of the silicones exposed to the beverages (P < .05). The value of ΔE was significantly higher for A-2186-F compared with VST-50 and Silfy (P < .05 in all beverages at 6 h). The color of the elastomers progressively changed while immersed in the beverages over 6 h. The change in color was significantly greater for coffee compared with tea (P < .05). ConclusionsThe color stability of nonpigmented silicone elastomers is inherently low, which contributes to the overall color change of silicone prostheses when they are exposed to beverages that contain pigments. The elastomer A-2186-F had greatest values of ΔE among the materials tested. Color changes of silicone prostheses can be lessened by selecting materials with consideration of color stability to improve their longevity and extend their period of use.

An Experimental Method to Evaluate the Contribution of Wood Substrate and Coating Film to the Light Induced Colour Changes of Wood Surfaces

The paper presents an original laboratory method developed to determine and compare the light-induced colour changes of uncoated and coated wood surfaces, while also allowing the highlighting and evaluation of the individual contributions of the substrate and coating film to the global effect. Two types of wood test samples: V1 (uncoated) and V2 (coated) and coating films on 1mm thick clear glass slides were employed. The behaviour of the wood substrate under the coating film was simulated on uncoated substrate covered with a coated glass slide. European maple (Acer pseudoplatanus L.) and two types of transparent water-based varnishes with 2k formulations were used. The samples were exposed for up to 72 hours to artificial UV-VIS light in accelerated tests simulating natural light passing through window glass. Colour changes were measured in the CIELab system, as well as the chemical changes of the wood substrate and the coating films by FTIR analysis. Exposure of uncoated maple wood resulted in a total colour difference (E) of 10.83 units and this was only slightly reduced by coating (9.29-9.81 units). Exposure through the glass slide reduced the colour changes of the uncoated and coated wood surfaces by 37-43%. Colour changes of 5.79-6.85 units were measured on the wood substrate exposed under coated glass slides, whilst the colour changes of the coating films on glass slides were only 0.64-1.0 units, which indicates a maximum contribution of the wood substrate to the light-induced colour changes of the coated surfaces. FTIR investigation confirmed this finding.

One-step reagentless colorimetric analysis platform of biomineralized Ce-UiO-66 for universal detection of biomarkers

Enzymatic colorimetric analysis system is a sensitive and facile onsite quantitative analysis methodology for disease diagnosis, which undergoes a two-step process: (1) H2O2 generation through catalytic oxidation of biomarkers (glucose, uric acid, xanthine, etc.) by corresponding oxidases and (2) catalytic production of reactive oxygen species from H2O2 by peroxidase/peroxidase-like nanozymes to induce color change of chemical chromogenic agents. However, natural enzymes and chemical chromogenic agents are easily oxidized/degraded under harsh environments, thereby being restricted to well-equipped laboratories and seriously limiting their applications. Herein, natural oxidase-encapsulated Ce-UiO-66 (oxidase@Ce-UiO-66), prepared via a facile one-step approach under mild conditions, was exploited to construct a reagentless colorimetric smartphone analysis platform for quantitative analysis of various disease biomarkers. Ce-UiO-66 as carrier of oxidases not only enhanced their stability under long-term storage but also preserved their activity for H2O2 generation through catalytic oxidation of biomarkers under various environments. Subsequently, Ce-UiO-66 served as a dose-dependent chromogenic agent of H2O2 due to the Ce-UiO-66-to-CeO2 phase transition, leading an apparent color evolution from white into orange. Based on the corresponding oxidase@Ce-UiO-66, the smartphone-enabled colorimetric analytic system was developed to achieve a facile, sensitive, and specific onsite detection of glucose (limit of detection (LOD): 35 μM and a wide range of 39–20,000 μM), uric acid (LOD: 21 μM and a wide range of 26–3400 μM), and xanthine (LOD: 3.9 μM and a wide range of 15.6–500 μM), giving their promises for clinic diagnosis.

Controlling coloring temperature of structurally colored emulsions using different alkyl chain lengths of surfactant

Structurally colored materials that respond to external stimuli have attracted considerable attention as emerging colors. Structurally colored materials are mainly based on periodic arrays of solids; however, all-liquid colored materials with variable shapes are rare. We previously reported that all-liquid emulsions composed of a long-chain amidoamine derivative (CnAA; n = 18) and tetraoctylammonium bromide develop structural color in a narrow temperature range and that temperature can induce color changes. However, the adjustable temperature range for coloration is narrow, and coloration at high temperatures was not achievable. In this study, we investigated the effect of alkyl chain length of CnAA on coloring behavior and temperature range, and demonstrated that coloring-temperature range can be considerably increased (up to ∼65 °C) by shortening the chain length. The advantage of thermally induced color change is retained by changing the chain length. For any CnAA, the color is blue-shifted upon heating to higher temperatures, and color tone is tunable via CnAA concentration. Furthermore, mixing CnAAs with different chain lengths is effective in adjusting the coloring temperature, allowing precise control of the coloring temperature according to the mixing ratio.

Investigation of vapochromism of 3,3′,5,5′-tetramethylbenzidine-tetrasilicicfluormica intercalation compounds through visible diffuse reflection and powder X-ray diffraction

In this study, we synthesized intercalation compounds of 3,3′,5,5′-tetramethylbenzidine (TMB) and tetrasilicicfluormica (TSFM) via a commonly used cation exchange method with TMB2+/TSFM cation exchange capacity (CEC) ratios of 1.0, 2.0, 2.7, and 5.4. These materials were characterized using powder X-ray diffraction (XRD), X-ray fluorescence, thermogravimetric-differential thermal analysis, scanning electron microscopy, and visible absorption spectroscopy. The vapochromism of each sample was assessed directly from the exterior of the glass sample tube using diffuse reflectance spectroscopy. All specimens vacuum-dried at 50 °C appeared yellow but turned green under water vapor at TMB/CEC = 2.0, 2.7, and 5.4, and blue under acetonitrile vapor at all TMB/CEC ratios. The sample with TMB/CEC = 2.0, in particular, exhibited clear vapochromic effects towards water and acetonitrile. Methanol and formic acid induced color changes similar to that of water vapor but less intense, except at TMB/CEC = 2.0. The color of each sample faded upon exposure to gaseous ammonia, whereas ethanol, acetone, iodomethane, and nonpolar solvents did not induce any color changes. The powder XRD pattern suggested changes in the array structures of TMB in the interlayer spaces due to vapor exposure.

A portable smartphone-based colorimetric sensor that utilizes dual amplification for the on-site detection of airborne bacteria

Over the past few years, infections caused by airborne pathogens have spread worldwide, infecting several people and becoming an increasingly severe threat to public health. Therefore, there is an urgent need for developing airborne pathogen monitoring technology for use in confined environments to enable epidemic prevention. In this study, we designed a colorimetry-based bacterial detection platform that uses a clustered regularly interspaced short palindromic repeat–associated protein 12a system to amplify signals and a urease enzyme to induce color changes. Furthermore, we have developed a smartphone application that can distinguish colors under different illumination conditions based on the HSV model and detect three types of disease-causing bacteria. Even synthetic oligomers of a few picomoles of concentration and genomic DNA of airborne bacteria smaller than several nanograms can be detected with the naked eye and using color analysis systems. Furthermore, in the air capture model system, the bacterial sample generated approximately a 2-fold signal difference compared with that in the control group. This colorimetric detection method can be widely applied for public safety because it is easy to use and does not require complex equipment.

Field retrieved photovoltaic backsheet survey from diverse climate zones: Analysis of degradation patterns and phenomena

Understanding the impact of climate stressors on photovoltaic (PV) backsheet degradation in real-use conditions is critical to improve the accelerated testing exposures, extend the backsheet lifetime, and increase the confidence in PV reliability. In this work, a total of 33 PV module backsheets were retrieved from six climatic zones worldwide with 2 - 28 years of exposure. These modules included five types of backsheet air-side materials (or outer layer): poly(vinylidene fluoride) (PVDF), poly(tetrafluoroethylene-co-hexafluoropropylene-co-vinylidene fluoride) (THV), poly(vinyl fluoride) (PVF), poly(ethylene terephthalate) (PET), and polyamide (PA). Attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) was used to identify air-side materials. The degradation induced color change, gloss loss, and chemical material changes analyzed using optical microscopy, differential scanning calorimetry (DSC), scanning electron microscopy (SEM), colorimetry (yellowness index (YI)), and gloss measurements. PVDF, THV, and PVF air-side layer backsheets, in particular PVF, had minimal degradation in the air-side layer appearance and chemical structures after exposure in different climatic zones. The PET air-side backsheets exhibited obvious color increase (22.55 YI units after about 9 years exposure) and the PA/PA/PA backsheets showed large gloss loss (up to 76.4 %) relative to the unexposed backsheets. Severe cracks between cells that penetrated through the entire thickness of backsheets are observed on PA/PA/PA backsheets after 4-6 years of exposure in 6 climatic zones. The current indoor exposure standards were not sufficient to identify this degradation type. However, fluoropolymer based PV backsheets showed lower levels of degradation predictors and increased climatic resistance. Specific samples (PVF) showed little change from baseline after 28 years of outdoor exposure.

Coffee Staining and Simulated Brushing Induced Color Changes and Surface Roughness of 3D-Printed Orthodontic Retainer Material.

This in vitro study evaluated the influence of combined coffee staining and simulated brushing-induced color changes and surface roughness on 3D-printed orthodontic retainers. Specimens measuring 10 × 10 × 0.75 mm3 were obtained either by conventional vacuum forming or 3D printing at four print angulations (0°, 15°, 30°, and 45°) (n = 10). The prepared specimens were immersed in a coffee beverage and then mechanically brushed using a simulating device. The specimen's color difference (ΔE) and surface roughness (Ra) were quantified using a spectrophotometer and a non-contact profilometer, respectively. The highest and lowest mean ΔE values were recorded for the 3D-printed-45° (4.68 ± 2.07) and conventional (2.18 ± 0.87) groups, respectively. The overall mean comparison of ΔE between the conventional and 3D-printed groups was statistically significant (p < 0.01). After simulated brushing, all groups showed a statistically significant increase in the Ra values (p < 0.01). The highest Ra was in the 3D-printed-45° (1.009 ± 0.13 µm) and conventional (0.743 ± 0.12 µm) groups, respectively. The overall ΔE of 3D-printed orthodontic retainers was not comparable to conventional VFRs. Among the different angulations used to print the retainers, 15° angulations were the most efficient in terms of color changes and surface roughness and were comparable to conventional VFRs.

Smartphone-based non-invasive haemoglobin level estimation by analyzing nail pallor

Blood haemoglobin concentration is a vital physiological parameter for assessing disease conditions, such as Anaemia in the human body. Anaemia is one of the most common diseases that affects billions of people worldwide. Especially, in developing countries, like India, the prevalence is quite high according to WHO statistics. Traditional invasive process for screening of anaemia is exorbitant and is hard to orchestrate in a resource-poor environment which raises the demand for cost-effective, reliable, portable, non-invasive solution. Hence, in this work, we aim to design a solution for non-invasive screening of anaemia by combining the cutting-edge Artificial-Intelligence techniques with the conventional practises for rough assessment of anaemia by observing pallor in the finger-nail of hand of a human subject. The proposed method first induces color changes in nail-bed by application of suitable amount of pressure and release thereafter through a customized hardware device. Finally, the captured video by a smartphone camera is analysed to measure the rate of change of color to quantify the blood haemoglobin level after correlating with the clinically determined value of blood haemoglobin. The proposed model with a fusion-based prediction approach outperforms the state-of-the-art solutions, ensuring a mean RMSE and MSE error of 0.63 and 0.61 and standard deviation ± 0.46 g dL−1 and ± 0.73 g dL−1 respectively as compared to clinically tested haemoglobin level for a total of 220 subjects.

Chrono-colorimetric sensor array for detection and discrimination of halide ions using an all-in-one plasmonic sensor element

Most nanoparticle based colorimetric sensor array utilize several sensor elements and static response for discrimination of target analytes. This approach can be complicated and costly to synthesize or functionalize different nanoparticles for providing wide color variation. Herein, triangular silver nanoparticles (TSNPs) were used to develop a colorimetric sensor array by time-dimension responses. The principle of this sensor array is based on the diverse etching process of TSNPs in the presence of three halide ions, including bromide (Br−), iodide (I−) and chloride (Cl−). Various etchings of TSNPs induced color changes at different reaction time intervals, which produced a colorimetric pattern for each ion. Therefore, using time dependent etching responses of TSNPs as a single sensing component can produce a wide color variation which can be distinguished by naked eyes. The colorimetric responses of TSNPs upon the addition of different concentrations of halide ions have been analyzed by PLS regression (PLS-R) and PLS discriminant analysis (PLS-DA). The analytical figures of merit confirmed that the developed chrono-colorimetric TSNPs -based sensor array is successful in both the discrimination and quantitative detection of halide ions. At the final step, the three halide ions were accurately determined in a real water sample, which verified the potential of the developed sensor in a real sample.

Pressure tuning of optical reflectivity in LuH2

Recently, the claim of room-temperature superconductivity in nitrogen-doped lutetium hydride at near-ambient conditions has attracted tremendous attention. Criticism of the work rises shortly, while further explorations are needed to settle the dispute. One of the intriguing observations is the pressured-induced color change, which has been reproduced in the lutetium dihydride LuH2 while its mechanism remains unclear. Through optical reflectivity measurements of LuH2 in the visible to near-infrared region, we observe strong light absorption next to the sharp plasmon resonance, which continuously shifts to higher energies with increasing pressure. It gives rise to the increased reflection of red light and suppressed reflection of blue light. Our work sheds light on resolving the puzzles regarding the pressure induced color change in LuH2.

Pressure induced color change and evolution of metallic behavior in nitrogen-doped lutetium hydride

By applying pressures up to 42 GPa on the nitrogen-doped lutetium hydride (LuH2+xNy), we have found a gradual change of color from dark-blue to pink-violet in the pressure region of about 12 to 21 GPa. The temperature dependence of resistivity under pressures up to 50.5 GPa shows progressively optimized metallic behavior with pressure. Interestingly, in the pressure region for the color change, a clear decrease of resistivity is observed with the increase of pressure, which is accompanied by a clear increase of the residual resistivity ratio (RRR). Fitting to the low temperature resistivity gives exponents of about 2, suggesting a Fermi-liquid behavior in the low temperature region. The general behavior in a wide temperature region suggests that the electron-phonon scattering is still the dominant one. The magnetoresistance up to 9 T in the state under a pressure of 50.5 GPa shows an almost negligible effect, which suggests that the electric conduction in the pink-violet state is dominated by a single band. It is highly desired to have theoretical efforts in understanding the evolution of color and resistivity in this interesting system.