Optimal Doping Concentration Research Articles

Improvement of rewriting time of optically driven liquid crystal display by azo-dye doping

ABSTRACT Optically driving liquid crystal display (ODLCD) uses polarized light field to control the orientation of the liquid crystal, and the display content can be maintained without external electric field, with extremely low power consumption. However, it has a long rewriting time, which is difficult to achieve industrialization. In order to improve the rewriting performance, the influence of the rotational viscosity of the mixed system of azo-dyes (SD1, MR) and nematic liquid crystal (5CB) on the rewriting speed is investigated. The experimental results show that the electro-optical properties of SD1-5CB and MR-5CB have great changes after irradiation by polarized light, among which the SD1-5CB is the best to improve the performance. With the increase of SD1 concentration, the rotational viscosity of SD1-5CB decreases significantly due to the change of cis-trans isomerization of azo-dye, and the optimal doping concentration is 0.5 wt%. In this case, the rewriting time is shortened from 45 s to 11 s, which has the potential to broaden the application of ODLCD.

Structural and optical properties of Cd2MgTeO6:Dy3+, Na+ phosphors for potential application in w-LEDs and personal identification

Cd2MgTeO6:Dy3+, Na+ phosphors were synthesized via a high-temperature solid-phase reaction. Phase purity, structure, surface morphology, luminescent properties, and thermostability of the samples were analyzed exactly. Under 351 nm excitation, Cd2MgTeO6:Dy3+, Na+ phosphors possessed three emission peaks: 4F9/2-6HJ/2 (J = 15, 13, 11). The phosphors mainly emitted yellow light due to the intensity of 4F9/2-6H13/2 being higher than other energy level transitions. The optimal doping concentration of Cd2MgTeO6:xDy3+, xNa+ phosphor was x = 10 mol% and the mechanism of concentration quenching was the quadrupole-quadrupole interaction. The phosphors possessed good thermostability and high activation energy (Ea = 0.41 eV). The chromaticity coordinate (CIE) coordinates of Cd2MgTeO6:Dy3+, Na+ were located yellow region and were almost the same at different doping concentration. For Cd2MgTeO6: 10 mol%Dy3+, 10 mol%Na+ phosphor, the internal quantum efficiency (IQE) was 20.55% and the cell viability for the cytotoxicity test was bigger than 88.1%. White-light emitting diode (w-LED) was fabricated with an excellent correlated color temperature (CCT = 5340 K) and a high color rendering index (CRI = 88). Cd2MgTeO6:10 mol%Dy3+, 10 mol%Na+ phosphor could display the feature of latent fingerprint (LFP) and lip print (LP) excellently. Hence, the phosphor could excellently apply to the three-level features of latent fingerprint and six characteristics of lip print identification. In general, Cd2MgTeO6:Dy3+, Na+ phosphors have great potential in w-LEDs and personal identification.

Dual-emitting Dy3+/Eu3+ co-doped SrLaGaO4 phosphor: Tunable luminescence, energy transfer and ratiometric temperature sensing

Dy3+/Eu3+ co-doped SrLaGaO4 warm white phosphor was synthesized by solid state reaction and studied for the first time. Under 352 nm excitation, the obtained tetragonal SrLaGaO4: Dy3+ phosphor exhibit blue (483 nm) and yellow (577 nm) emission and the optimal doping concentration of Dy3+ is 5 mol%. After co-doping with Dy3+ and Eu3+ ions, phosphor emits warm white light and the correlated color temperature can be adjusted from 4745 K to 3004 K. The quantum yield of SrLaGaO4: 0.05Dy3+ and SrLaGaO4: 0.05Dy3+, 0.008Eu3+ are 11.3 % and 13.27 %, respectively. In addition, temperature-dependent spectra showed that Dy3+ and Eu3+ have different emission variations in SrLaGaO4: 0.05Dy3+, 0.012Eu3+ phosphor, which was explained by thermally induced energy transfer between Dy3+ and Eu3+ in configuration coordinate diagram. The fluorescence intensity ratios of Eu3+ and Dy3+ at 298 K- 423 K were calculated to analyze the temperature sensing properties. The maximum absolute sensitivity of SrLaGaO4: 0.05Dy3+, 0.012Eu3+ phosphor was obtained as 0.63 % K–1 at 298 K. Finally, the WLED device is prepared by SrLaGaO4: Dy3+, Eu3+ phosphor, which emits warm white light with a correlated color temperature of 3550 K. In summary, SrLaGaO4: Dy3+, Eu3+ are excellent single-phase warm white component applicated for WLED and optical thermometers.

Origin of Spin‐State Precise Modulation for Enhanced Oxygen Evolution Activity: Effect of Secondary Coordination Sphere

AbstractThe process of oxygen evolution reaction (OER) is crucial for energy storage and conversion, and the spin electronic structure of catalyst significantly influences its catalytic activity. Precisely regulating the spin electronic structures of metal active centers with intermediate spin (IS) states is challenging but important. This study presents a general method for achieving spin‐state precise modulation by altering the secondary coordination sphere (SCS) in Fe‐substituted LaCo1‐xFexO3 perovskites, denoted as Co6‐y−[Co]−Fey (y = 0–6). The concentration‐dependent SCSs can precisely regulate the spin state of Co3+ from high‐spin (HS) to IS and low‐spin (LS) state by tuning the Co─O binding energy of primary coordination sphere (PCS) to ≈567 KJ mol−1. The binding energy demonstrates a strong negative correlation with the spin state of Co3+, serving as a quantitative descriptor for precise spin‐state modulation. Furthermore, a universal optimal doping concentration is proposed for generating IS‐state Co3+ with the best OER activity, ranging from 1/(m+1) to 2/(m+1) in M‐doped ACo1‐xMxOy system with the coordination number of m. As a proof‐of‐concept, the LaCo7/9Fe2/9O3 with IS Co3+ exhibits significantly enhanced OER activity, almost six times higher than the control samples (without IS Co3+). These findings provide new insights into spin‐state modulation for effective OER catalysts.

Performance improvement of 263 nm AlGaN DUV LDs with different doping concentration and composition graded EBL Techniques

As part of this study, we present a study on the act of electrically driven Laser Diode (LD) using trinary Aluminum Gallium Nitride (AlGaN) with optimized doping concentrations. To increase the LD’s output power and capabilities, we focused on utilizing different doping concentrations in the electron-blocking layer (EBL). We conducted the calculations with PICS 3D software; we obtained simulation results indicating that the designed LD structure successfully emitted an ultraviolet (UV) laser class-c at a wavelength of 263.7 nm. By implementing this approach, we anticipate achieving higher optical output power by 6%, enhancing the concentration of electron and hole, and reducing the electron current density (356.1 to 342.8) and threshold voltage (4.516 to 4.5 V), and hole current density increases in AlGaN-based ultraviolet LDs. These promising outcomes can be attributed to the effective conduction band barrier height achieved by the optimized electron-blocking layer (EBL).

NaYF4:Yb3+/Ho3+ up-conversion luminescence and its low temperature sensing characteristics

Pure hexagonal [Formula: see text]-NaYF4 micron crystals were synthesized by the hydrothermal method with the up-conversion luminescence properties studied by doping Yb[Formula: see text]/Ho[Formula: see text]. The up-conversion fluorescence spectra and fluorescence lifetime of [Formula: see text]-NaYF4 micron crystals were determined by FLS-980 transient fluorescence spectrometer. By changing the doping concentration of Yb[Formula: see text]/Ho[Formula: see text], the optimal doping concentration was confirmed to be 20%Yb[Formula: see text]/2%Ho[Formula: see text]. The fluorescence spectrum was obtained by changing pump power, the relationship between power and intensity was analyzed, and the [Formula: see text]-NaYF4 micron crystal green and red emission up-conversion process was obtained into a two-photon process. The 5F[Formula: see text]I8 and 5S[Formula: see text]I8 of the sample were thermally coupled to obtain a large absolute sensitivity (Sa) of low temperature. The maximum absolute sensitivity within the range of 64–194[Formula: see text]K is 0.0097[Formula: see text]K[Formula: see text] at 144[Formula: see text]K, while maximum absolute sensitivity at 333[Formula: see text]K is 0.00335[Formula: see text]K[Formula: see text] in the range of 293–493[Formula: see text]K. The experimental results show that the sensing characteristics of [Formula: see text]-NaYF4:Yb[Formula: see text]/Ho[Formula: see text] at low temperature are better than those at high temperature, and it has the potential to be used in the field of temperature sensing.

Energy transfer mechanism and luminescence properties of green phosphors Sr2YF7: Dy3+, Tb3+

In this study, color-adjustable Sr2YF7: xDy3+, and yTb3+ light-emitting phosphors were synthesized through the hydrothermal method. Systematic experiments were performed to determine the optimal doping concentration for Sr2YF7: xDy3+ phosphor with x = 0.03, resulting in a distinctive light blue emission band attributed to the 4F9/2 → 6H15/2 transition. The energy transfer within the double-doped system of Sr2YF7: Dy3+, yTb3+ (y = 0, 0.06–0.1) was examined by analyzing spectral overlap and reductions in emission lifetimes. Moreover, the mechanism governing this energy transfer phenomenon was investigated. The concentration proportion of Dy3+/Tb3+ in Sr2YF7 phosphors was modulated to achieve color modulation, transitioning from light blue to vibrant green emissions in Sr2YF7: Dy3+, Tb3+ samples. The intensity of green emission increased with increasing Tb3+ ion concentrations because of the dynamics of energy migration from Dy3+ to Tb3+ levels (4F9/2 + 7F6 → 6H15/2 + 5D4). Based on calculations using steady-state rate equations, Tb3+ ion doping effectively reduced ionic spacing and consequently amplified the green emission. Furthermore, the results indicated that the luminous intensity ratio of Sr2YF7: 0.03Dy3+, 0.07 Tb3+ phosphors at 423/303K was notably high at 93.59 %, indicating high thermal stability. Thus, Sr2YF7 phosphors co-doped with Dy3+ and Tb3+ emerge as potential candidates for application in advanced illumination technologies.

Preparation and strong green upconversion luminescence of Ca9Y(VO4)7: Yb3+/Er3+ phosphor

Exploring novel oxysalt compounds remains significant due to their affordability and versatile applications, such as serving as laser crystals, piezoelectric crystals, frequency-doubling crystals, and luminescent materials. Specifically, this study introduces a new near-single green upconversion luminescent Ca9(VO4)7: Yb3+/Er3+ material, synthesized through high-temperature solid-phase methods. When subjected to 980 nm near-infrared laser irradiation, the Ca9(VO4)7: 0.3 Yb3+, 0.02 Er3+ phosphor demonstrates robust green luminescence at 531 nm (2H11/2 → 4I15/2) and 558 nm (4S3/2 → 4I15/2), accompanied by faint red luminescence at 665 nm (4F9/2 → 4I15/2). The optimal doping concentrations for Yb3+ and Er3+ ions, yielding the highest upconversion luminescence intensity, are determined to be 0.3 and 0.02, respectively. The investigation elucidates the upconversion luminescence mechanism through the downward shift spectrum in photoluminescence and the pumping power dependence of upconversion green-red luminescence. The primary excitation pathway identified for the upconversion process in Ca9Y(VO4)7: 0.3 Yb3+, 0.02 Er3+ involves Yb3+ (2F5/2) + Er3+ (4I11/2) → Yb3+ (2F7/2) + Er3+ (4F7/2). This research contributes to the exploration of new materials, injecting vitality into modern industries and production processes.

Development of thermally stable red-emitting lead-free double-perovskite phosphors with an internal PLQY approaching 100.

White light-emitting diode (WLEDs), acting as a new generation of solid-state lighting, play a critical role in energy conservation. Red-emitting phosphors with high efficiency could effectively improve the quality of WLED devices. In this report, Eu3+-doped Ca2ScTaO6 luminescent materials have been successfully synthesized by a high-temperature solid-state method. Its crystal structure was confirmed to be a monoclinic lead-free double-perovskite material system with the space group P21/n by the X-ray diffraction patterns. The strongest emission peak was about 614 nm distributed to the 5D0 → 7F2 electric-dipole transition. Additionally, the optimal doping concentration was found to be 40 mol%, and the concentration quenching mechanism is assigned to d-d interactions. The Ca2ScTaO6:Eu3+ phosphors exhibited an ultrahigh internal quantum yield (about 100%) with good thermal stability (81.5% at 423 K compared with the emission intensity at 303 K). Furthermore, a WLED with a suitable correlated color temperature (4201 K) and a color rendering index (87.62) was fabricated. The phosphor-based polydimethylsiloxane light-emitting flexible film exhibited good luminescence, which is suitable to be utilized in flexible displays. The obtained results suggest that the high-efficiency red-emitting Ca2ScTaO6:Eu3+ phosphors are promising commercial candidates for use in near-ultraviolet-excited WLEDs.

First-principles calculations of structural and magnetic properties of SmCo<sub>3</sub> alloys doped with transition metal elements

Among the spectra of rare-earth permanent magnetic materials, the Sm-Co-based alloys stand out with their excellent magnetic properties in high-temperature environments. However, the practical applications of these alloys in high-temperature settings face constraints due to their comparatively lower saturation magnetization and structural stability. In this study, Fe, Ni, Cu, and Zr are used as representative transition metal elements to investigate the effects of doping elements on the structural stability, magnetic properties, and electronic structure of SmCo<sub>3</sub> alloy by first-principles calculations. The findings indicate that the doping of elements Ni, Cu, and Fe contributes positively to enhancing the structural stability of the SmCo<sub>3</sub>, while the introduction of Zr element has an adverse effect. Magnetic property calculations reveal that the incorporation of non-magnetic elements leads the total magnetic moment of the SmCo<sub>3</sub> to decrease to a certain extent, whereas the introduction of magnetic elements can enhance the total magnetic moment. Notably, not all doped magnetic elements in the SmCo<sub>3</sub> result in an increasing total magnetic moment. The underlying microscopic mechanisms are elucidated through electronic structure analysis. Finally, it is screened out that the transition element Fe is beneficial to improving the magnetic properties and structural stability of SmCo<sub>3</sub>, and the doping concentration (atomic percentage) in its unit cell ranges from 0 to 22.22%, the optimal doping concentration (atomic percentage) is predicted to be 18.52%.

Novel Sm3+-doped La3Ga5MO14 (M = Si or Ge) phosphors for indoor illumination: effects of M cations on photoluminescence.

A series of La3(1-x)Ga5MO14:xSm3+ (M = Si or Ge) orange-red phosphors with high color purity, low correlated color temperature, and good thermal stability were successfully synthesized via a high-temperature solid-phase technique. The phase structure and morphology of La3Ga5SiO14(LGSi):xSm3+ and La3Ga5GeO14(LGGe):xSm3+ were investigated. Sm3+-doped LGSi and LGGe phosphors emitted orange-red light under an excitation of 403 nm, and the optimal doping concentrations were 3 mol% and 2 mol% with excellent color purities of 98.46% and 98.25%, respectively. The concentration quenching mechanism of both the samples was dominated by dipole-dipole interaction, and the effect of Si4+ and Ge4+ on luminescence performance was discussed. The internal quantum efficiencies of LGSi:0.03Sm3+ and LGGe:0.02Sm3+ were calculated to be 27.14% and 56.07%, respectively. The CIE and CCT values indicated that the luminescence of the prepared phosphors was in the orange-red region. Additionally, a white light-emitting diode (w-LED) was fabricated with LGGe:0.02Sm3+ phosphors, which was capable of emitting bright and warm white light and exhibiting a high color rendering index (CRI) of 87.17 and an appropriate correlated color temperature (CCT) of 6108 K. These results indicated that the prepared phosphors with excellent luminescent performances have potential application in indoor illumination.

The Sr(La1-xTbx)AlO4 (x= 0–1) type layered perovskite: Full substitution of La site, restrained photoluminescence concentration quenching, and novel long afterglow luminescence

A series of Tb3+ substituted layered perovskite Sr(La1-xTbx)AlO4 (x = 0–1) was synthesized via solid-state reaction. The influence of Tb3+ on the phase, structure, photoluminescence, and long afterglow properties of the SrLaAlO4 product was investigated. The fully substituted product SrTbAlO4 was found to be isostructural with its SrLaAlO4 counterpart, and the crystal structure parameters were first reported in this work. Photoluminescence investigation found that benefiting from the unique layered crystal structure, the activator Tb3+ was well separated and the optimal doping concentration was found to be as high as 20 at%. Except for photoluminescence, the products simultaneously show long afterglow properties due to disorder cations distribution in the local structure and thus induced defect condition. When the UV light source is turned off, the afterglow luminescence of SrLaAlO4: 0.03 Tb3+ can last over 1 h. The trap distribution of SrLaAlO4: Tb3+ was analyzed in detail by thermoluminescence. The trap depth is calculated to be around 0.7–0.81 eV, the value of which highly coincides with the ideal energy level for trapping and releasing electrons at room temperature. On the basis of the experimental results, the mechanism of long afterglow luminescence of SrLaAlO4: Tb3+ is elaborated and discussed.

Preparation and properties of novel tungstate SrLa6W10O40: Eu3+ phosphors

Novel tungstate SrLa6-xW10O40: xEu3+ (x = 0, 0.03, 0.06, 0.09, 0.12, 0.15, 0.18, 0.21) red phosphors were prepared by solid state method at 1150 ?C by using SrCO3, La2O3, WO3 and Eu2O3 as raw materials. The powders were agglomerated with particles having mostly spheroidal morphology, mean particle size D50 = 12.8 ?m and narrow particle size distribution. With the increase of doping amount x, there is no significant difference in the diffraction peak position of the phosphor, but the cell volume of SrLa6W10O40 slowly decreases. The relative strength of diffraction peaks decreases gradually and the half-peak width widens gradually, indicating that the inclusion of Eu3+ ions affects the crystallization of the SrLa6W10O40 matrix. Excitation and emission spectra of the prepared samples were obtained. The optimal doping content has the SrLa5.85W10O4: 0.15Eu3+ phosphor and is characterised with the colour coordinate of (0.652, 0.348), which is closer to the red standard colour (0.67, 0.33) than the near-ultraviolet red phosphor Y2O2S: Eu3+ (0.622, 0.351) used for commercial LED.

Luminescence properties and Judd-Ofelt analysis of Tb3+ doped Sr2YTaO6 double perovskite phosphors for white LED applications.

A series of Tb3+-doped Sr2YTaO6 double perovskite phosphors (SYT:Tb3+) were synthesized using a conventional solid-state reaction method. A strong green emission was observed in the SYT:Tb3+ phosphors, and the optimal doping concentration of Tb3+ was confirmed to be 5 mol%. The electric dipole-dipole interaction was ascribed to be the main mechanism for the luminescence concentration quenching. Analysis of the concentration-dependent fluorescence decay confirmed that the self-generated quenching model holds for the dynamic process of Tb3+ decays in SYT. Furthermore, the internal quantum efficiencies, non-radiative transition rates, and energy transfer rates of the 5D4 level for the SYT:Tb3+ samples were estimated, respectively. The luminescence thermal stability of the sample was also evaluated based on the Arrhenius model. The chromaticity shift of the SYT:5 mol% Tb3+ phosphor was examined to be 0.013 when the sample temperature was increased from 303 to 483 K, thus indicating excellent chromaticity shifting resistance under high temperature conditions. Moreover, the Judd-Ofelt parameters were calculated from the emission spectra of SYT:Tb3+ to be Ω2 = 0.29 × 10-20, Ω4 = 0.45 × 10-20, and Ω6 = 0.72 × 10-20 cm2, respectively. The fluorescence branching ratios and radiative transition rates for the 5D4 level were calculated based on the obtained Judd-Ofelt parameters. Finally, a white light-emitting diode (LED) prototype was assembled using a 310 nm LED chip combined with a prepared green SYT:Tb3+ phosphor and two other commercial blue and red phosphors. The obtained warm white light exhibits good chromaticity coordinates (0.32, 0.32) and a high color rendering index of 96.1. Based on the above results, it can be known that the prepared SYT:Tb3+ phosphors have a potential application as green emitting phosphors in white LEDs.

Broadband near-infrared (NIR) emitting Cr3+ -doped La3 Ga5 SnO14 phosphor with long persistent and photostimulated persistent luminescence.

Recently, long persistent phosphors (LPPs) have attracted significant attention as promising candidates for biomedical applications. However, the serious decrease in luminescence intensity in tissue still remains a major challenge. Therefore, exploring more competitive LPPs and achieving reproducible tissue imaging is crucial. In this study, a new series of near-infrared (NIR) phosphors La3 Ga5 Sn1-x O14 :xCr3+ (x = 0.005-0.05) were synthesized using a high-temperature solid-state method. The as-synthesized samples were characterized using X-ray diffraction, diffuse/photoluminescence spectroscopy, fluorescence decay curves, and thermoluminescence spectroscopy. Upon excitation with ultraviolet light, strong emission bands were observed in the range 600-1200 nm with an optimal doping concentration of x = 0.02mol. Moreover, La3 Ga5 SnO14 :Cr3+ exhibits persistent luminescence due to the presence of suitable energy traps, which prompted the phosphor to emit NIR light even after the removal of the excitation source.

Novel high-sensitivity optical thermometry based on fluorescence intensity ratio of <inline-formula><tex-math id="Z-20240425115725">\begin{document}${\text{VO}}_4^{3 - } $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="9-20240012_Z-20240425115725.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="9-20240012_Z-20240425115725.png"/></alternatives></inline-formula> to Pr<sup>3+</sup>

It is noteworthy that since 2010, the number of published and cited scientific papers on optical thermometry has increased exponentially. Optical thermometry technology is about to make a significant process in sensing, therapy, diagnosis, and imaging. The current research mainly focuses on optical thermometry that is developing towards high-sensitivity thermometry. In this work, a new thermometry strategy is proposed based on the different temperature-dependent behaviors between the host ions and the doped ions. Firstly, YVO<sub>4</sub>:<i>x</i>Pr<sup>3+</sup>(<i>x</i> = 0%–1.5%) phosphors are successfully synthesized by the solid-state method. Then, the structure and luminescence properties of the samples are characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and fluorescence spectrophotometer. The XRD results show that Pr<sup>3+</sup> ions are successfully incorporated into the YVO<sub>4</sub> host, and the sample has a tetragonal phase crystal structure with space group <i>I</i>41/<i>amd</i>. The SEM results show that the samples are rectangular-shaped micron particles with smooth surfaces, and the average grain size is about 2.1 μm. Under the excitation of 320 nm, the sample mainly exhibits broadband blue emission around 440 nm and red emission at 606 nm, which are attributed to the charge transfer transition of <inline-formula><tex-math id="M2">\begin{document}${\text{VO}}_4^{3 - }$\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="9-20240012_M2.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="9-20240012_M2.png"/></alternatives></inline-formula> and the <sup>1</sup>D<sub>2</sub>→<sup>3</sup>H<sub>4</sub> transition of Pr<sup>3+</sup>, respectively. The relationship between the luminescence of the sample and the concentration of Pr<sup>3+</sup> is studied. It is found that the optimal doping concentration of Pr<sup>3+</sup> is 0.5%, and a higher doping concentration will cause concentration to be quenched. The reason for quenching concentration is the electric dipole-quadrupole interaction. The luminescence peak position of the temperature-dependent spectrum of YVO<sub>4</sub>:0.5%Pr<sup>3+</sup> is consistent with that at room temperature. As the temperature increases, the total luminescence intensity gradually decreases, which is caused by thermal quenching, and the mechanism of thermal quenching is analyzed. Since the temperature-dependent behaviors of luminescence of <inline-formula><tex-math id="M3">\begin{document}${\text{VO}}_4^{3 - }$\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="9-20240012_M3.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="9-20240012_M3.png"/></alternatives></inline-formula> and Pr<sup>3+</sup> are significantly different from each other, a new fluorescence intensity ratio thermometry strategy is realized. Temperatures range is 303–353 K, and the maximum absolute sensitivity and relative sensitivity are 0.651 K<sup>–1</sup> and 3.112×10<sup>–2</sup> K<sup>–1</sup> at 353 K, respectively, much higher than the traditional thermally coupled level thermometry strategy. In addition, there is no obvious overlap between the emission peaks of <inline-formula><tex-math id="M4">\begin{document}${\text{VO}}_4^{3 - }$\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="9-20240012_M4.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="9-20240012_M4.png"/></alternatives></inline-formula> and Pr<sup>3+</sup>, which provides a good discrimination capability for signal detection. The above results show that this work provides a promising path for designing self-reference optical thermometry materials with excellent temperature sensitivity and signal discrimination.

Long wavelength near-infrared II emitting Na<sub>3</sub>YSi<sub>3</sub>O<sub>9</sub>:<i>x</i> Cr<sup>3+ </sup>silicate and spectral broadening by multi-site occupancy

Phosphors-converted near-infrared LED (pc-NIR LED) possesses applications in various fields including food quality analysis, night vision, biomedical imaging, and biomedicine. The design and development of broadband near-infrared (NIR) phosphors with the required properties are of decisive significance for pc-NIR LED devices. The Cr<sup>3+</sup> doped phosphors are considered to be most promising near-infrared materials for commercialization. Broadband NIR luminescent materials doped with Cr<sup>3+</sup> have attracted more and more attention due to their potential applications in NIR light sources. However, the emission wavelength of Cr<sup>3+</sup> doped phosphor is generally located in the NIR I region of less than 850 nm, and realizing the NIR II region emission is still a challenge. In this work, a series of Cr<sup>3+</sup> doped Na<sub>3</sub>YSi<sub>3</sub>O<sub>9</sub> new silicate phosphors is prepared by solid-state method in N<sub>2</sub> atmosphere at 1150 ℃ for 8 h. We take advantages of the silicate nature and the multi octahedral sites suitable for Cr<sup>3+</sup> in the studied Na<sub>3</sub>YSi<sub>3</sub>O<sub>9</sub> materials to redshift and broaden the spectrum. The phase, crystal structure, microstructure, photoluminescence, main emission peak decay and thermal stability of the samples are systematically studied. The results show that the prepared samples are pure phases, with uneven morphology, slight agglomeration, and the sizes in the micrometer range. The Cr<sup>3+</sup> is located in the weak crystal field environment of Na<sub>3</sub>YSi<sub>3</sub>O<sub>9</sub> lattice, with a <i>Dq</i>/<i>B</i> value of 2.29. Under the excitation of blue light at a wavelength of 485 nm, the strongest emission peaks of Na<sub>3</sub>Y<sub>1–<i>x</i></sub> Si<sub>3</sub>O<sub>9</sub>:<i>x</i> Cr<sup>3+</sup> phosphors are located at 984 nm (NIR II region), which is longer than those of most Cr<sup>3+</sup> activated phosphors. Due to the multi-site occupation of Cr<sup>3+</sup> in the lattice, the full width at half maximum (FWHM) of the emission spectrum is as high as 183 nm. The optimal doping concentration of Na<sub>3</sub>Y<sub>1–<i>x</i></sub> Si<sub>3</sub>O<sub>9</sub>:<i>x</i> Cr<sup>3+</sup> is 3%, and the quenching mechanism is the dipole-dipole interaction between Cr<sup>3+</sup> ions. Fluorescence decay curves show that the luminescence lifetime of Na<sub>3</sub>Y<sub>0.97</sub>Si<sub>3</sub>O<sub>9</sub>:0.03Cr<sup>3+</sup> sample gradually decreases with the increase of doping concentration and temperature. The results of the temperature-dependent spectra show that the emission intensity decreases in a temperature range from 298 K to 423 K, and the activation energy Δ<i>E</i> of Cr<sup>3+</sup> is 0.157 eV.

An efficient rare-earth free deep red-emitting GdGeSbO6:Mn4+ phosphor for white light-emitting diodes.

Red phosphors play an important role in improving the light quality and color rendering index of white light-emitting diodes (WLEDs) for lighting. In this paper, we report the transition ion Mn4+-activated deep red phosphor GdGeSbO6:x%Mn4+ and analyze its crystal structure, composition and luminescence behavior in detail. Its optimal doping concentration of Mn4+ is 0.3%. Under ultraviolet (UV) excitation, GdGeSbO6:0.3%Mn4+ produces a narrow emission peak centred at 682 nm in the range of 650-800 nm with a full width at half maximum (FWHM) of 25 nm, which is attributed to the spin-prohibited 2Eg → 4A2g transition of Mn4+ ions. Notably, the optimal phosphor GdGeSbO6:0.3%Mn4+ has a high internal quantum efficiency (IQE ≈ 65%) and excellent thermal stability performance (I423 K/I303 K ≈ 62%). The synthesis of high-performance warm WLEDs and full-spectrum WLEDs was achieved by combining and coating GdGeSbO6:0.3%Mn4+ phosphors with commercial phosphors on the surface of a 365 nm UV chip.

Improved energy storage density in La-doped PbZr0.95Ti0.05O3 films with stress regulation

The Pb1–1.5xLaxZr0.95Ti0.05O3 films with different La3+ contents were successfully prepared on the LaNiO3/SiO2/Si substrates by sol-gel method. The effect of La3+ doping on the microstructure, electrical properties, and energy storage performance of the films are systematically investigated. It is found that the introducing of La3+ with a smaller tolerance factor could enhance the lattice distortion and compressive stresses, leading to smaller grain size, slimmer electric hysteresis loops, and lower phase transition field hysteresis. As a result, a relatively high energy storage density of 30.2 J/cm3 together with the energy storage efficiency of 62.2% has been achieved in Pb0.82La0.12Zr0.95Ti0.05 antiferroelectric thin films with the optimum doping content. This improvement is largely attributed to the enhanced breakdown field strength from 1442 kV/cm to 1564 kV/cm as a result of grain size reduction. Our results demonstrate the crucial role of decreased tolerance factor in stabilizing the antiferroelectric phase and enhancing the phase transition electric field, and provide an effective route to enhance the energy storage performance of antiferroelectric thin films.

Europium-doped strontium gadolinium oxide phosphor: Investigating structural and photoluminescence characteristics via sol-gel combustion synthesis

SrGd2O4 phosphors doped with Eu3+ were successfully synthesized through a sol-gel combustion method, covering a range of dopant concentrations from 0.25 mol% to 3 mol%. The structural analysis of these phosphor materials was comprehensively conducted utilizing various techniques, including X-ray powder diffraction analysis (XRD), Energy Dispersive X-ray (EDX), and Fourier-transform infrared spectroscopy (FTIR). In addition to unveiling the structural characteristics, these analyses provide valuable insights into the compositional aspects, enhancing our understanding of the synthesized SrGd2O4:Eu3+ phosphors across different doping levels. XRD analysis findings validate the successful generation of the intended SrGd2O4 host, demonstrating orthorhombic system structures consistent with JPCD card number 98-019-3592. FTIR analyses conducted on the phosphor samples not only identify bending modes but also reveal intricate details about small vibration bonds within the material. When excited by the 349 nm laser, SrGd2O4:xEu3+ phosphors exhibit distinct photoluminescence (PL) properties like red emission at 614 nm from Eu3+. From the emission spectra, one can clearly observe that Eu3+ with an ionic radius close to the Gd3+ ion preferentially occupies the symmetry sites of the host lattice. The optimal doping concentration was determined to be 0.5 mol%, as revealed by the data in our study. Additionally, a deeper understanding of the luminescence quenching mechanism was attained, pinpointing the involvement of dipole-dipole (d-d) energy transfer in this intriguing phenomenon. This optimal concentration not only enhances the material's properties but also underscores the pivotal role of d-d interactions in governing the luminescence behavior within the doped system.