Green UC Research Articles

Synthesis and upconversion color Tunability luminescence of K5Yb(MoO4)4 phosphor doped with Er3+and optical temperature sensing applications

A series of double molybdates with palmierite-related structure phosphors K5Yb1-x (MoO4)4:xEr3+ were synthesized by a solid-state method. It has been demonstrated that the K5Yb1-x (MoO4)4: xEr3+ phosphors are capable of exhibiting the characteristic green and red UC emission of Er3+ ions with excitation at 980 nm. Moreover, the green light emission is far more than the red light emission, so that the sample emits a powerful green light, which belongs to the two-photon absorption process. The upconversion efficiency is peaked when the content of Er3+ ions is 10 mol %. The optical thermometry properties of phosphors were explored by observing that the green UC emission intensity is temperature dependent. The maximum sensor sensitivity of the studied phosphor was discovered to be about 1.61%K−1 at the optimum doping concentration. And the phosphor is demonstrated to have high thermal stability by temperature cycling test. Eventually, a green light-emitting diode device was realized by using synthesized particles and a 980 nm near-infrared chip, which can emit a more obvious green light when the voltage reaches 1.80 V and the current can reach 800 mA, thus confirming its applicability in solid-state lighting. And the LED devices have been tested for life stability with little or no light degradation. These properties make the phosphors not only suitable for non-contact optical temperature measurement, but also able to be applied to solid state lighting.

Strategic Approaches in Educational Administration and Management for Advancing Sustainable Development

Background and Aims: Educational administration and management are essential for advancing sustainable development because they shape the policies, leadership, and practices that underpin institutional sustainability initiatives. Sustainable governance and operations can foster an environmental culture and prepare students to face global challenges. This paper aims to identify, analyze, and evaluate strategic approaches for advancing sustainable development. Methodology: The methodology combines a systematic literature review with stringent data collection and analysis procedures to comprehensively examine strategic approaches in educational administration and management. The study employs a variety of data sources and analytical tools to identify effective practices, emerging trends, and gaps in the literature, providing important insights into advancing sustainable development in education. Results: The finding found that integrating sustainability into educational administration and management is critical for fostering an environmental stewardship culture and achieving long-term goals. Effective policies, transformational leadership, and active stakeholder engagement are critical to driving successful sustainability initiatives. Successful case studies, such as the Green School and UC Berkeley, demonstrate that by incorporating sustainability into the curriculum and leveraging technological innovations, educational institutions can address future challenges while increasing operational efficiency. Conclusion: Integrating sustainability into educational administration and management is critical for developing an environmental stewardship culture and meeting long-term objectives. The Green School and UC Berkeley have demonstrated how effective policies, leadership, and stakeholder engagement can improve operational efficiency and address future challenges by incorporating sustainability into curriculum and technology.

Morphology controlled synthesis and sensitive temperature sensing performance of Gd2(WO4)3: Er3+, Yb3+

Rare-earth ion doped negative thermal expansion materials as fluorescent thermosensitive materials have attracted significant attention due to their natural advantage in achieving high resolution fluorescence. Herein, Er3+/Yb3+-codoped Gd2(WO4)3 microparticles were developed. Their morphology and size can be finely controlled by manipulating the additives, pH values, and reaction rates. Under near-infrared (NIR) excitation, the compounds evince green and red UC emissions. With regards to the thermal coupling level of 2H11/2/4S3/2 of Er3+ ions, the maximum absolute sensitivity (Sa) and relative sensitivity (Sr) were established to be 1.39 % K−1 (at 300 K) and 1.18 % K−1 (at 293 K), respectively. Ultimately, the utilization of synthesized microparticles and a 940 nm NIR chip facilitated the development of a proficient green-emitting light-emitting diode device. The aforementioned characteristics indicate that Er3+/Yb3+ co-doped Gd2(WO4)3 microparticles possess potential applications in the fields of non-contact optical temperature sensing as well as solid-state lighting.

Efficient tunable temperature sensitivity in thermally coupled levels of Er3+/Yb3+ co-doped BaBi2Nb2O9 ferroelectric ceramic

Er3+/Yb3+ co-doped ferroelectric ceramic BaBi2-0.04-yNb2Er0.04YbyO9 (y = 0.00, 0.02, 0.04, 0.06, 0.08, 0.10, and 0.12) are prepared by solid-state method and investigated for their structural and upconversion luminescence properties. High-resolution X-ray pattern investigation confirmed the ceramic's orthorhombic structure. Microstructure of sintered ceramic surface resembles plate-like structures and consists of non-uniform grains that are randomly oriented. Upconversion luminescence (UCL) spectra revealed two prominent green emission bands near 535 and 557 nm and a notable red band at 672 nm, corresponding to a 980 nm excitation wavelength. Decay time measurements support the effective energy transfer from Yb3+ to Er3+ ions. The average lifetime increases with increasing Er3+/Yb3+ doping concentration up to the optimal concentration (y = 0.10). Pump power dependence demonstrates that two photons are required to generate green and red UC illumination. The absolute sensitivity, Sa (0.69% K−1 and 0.58% K−1) and relative sensitivity, Sr (1.1% K−1 and 1.01% K−1) have been recorded for the first time on Er3+/Yb3+ co-doped BaBi2-0.04-yNb2Er0.04YbyO9 ceramic at y = 0.06 and 0.10, respectively, suggesting it is a viable non-contact sensor ceramic whose sensitivity can be tuned by varying dopant concentrations.

Effect of adding TiO2 as modifier on the optical thermometric ability of tellurium tungstate glass

This work investigates the effect of incorporating TiO2 on the optical properties of the Er3+/Yb3+ doped/codoped tungstate-based tellurite (TW) glasses. The optical bandgap and Urbach energy analysis indicates that the structure of the binary tungstate glass gets modified due to the incorporation of TiO2. The Judd-Ofelt analysis shows that the bonding between the activator and ligand oxygen ions is ionic in nature and the ionicity of the bond increases with the TiO2 content. The incorporation of TiO2 enhances the green and red UC emission intensity of the Er3+ doped TW (TW_0.6) glass by ∼ 39 and ∼ 140 times respectively. The relative sensitivity of the Er3+/Yb3+: TW glass having 10 mol% of TiO2 is found to be as high as ∼ 0.01236 K−1 at 300 K.

A novel K3(Y0.88Yb0.10Er0.02)Si2O7 silicate phosphor for multi-mode thermometry of high sensitivity through up-conversion luminescence

Non-contract optical thermometry shows great advantages for temperature measurement in harsh environments, and it is highly desired to develop novel and high-performance systems. In this work, a novel K3(Y0.88Yb0.10Er0.02)Si2O7 phosphor was synthesized via solid-state reaction, and its up-conversion luminescence and optical thermometric performance were systematically investigated. Under 980 nm excitation, the K3(Y0.88Yb0.10Er0.02)Si2O7 phosphor showed a strong green UC emission through a three photon process. The phosphor was found well capable of sensing temperature via the multi-modes of fluorescence intensity ratio (FIR) of thermally/non-thermally coupled energy levels and fluorescence lifetime (FL). The maximum absolute (SA) and relative (SR) sensitivities are SA = 156 × 10−4 K−1 (I531/I555, 298 K) and SR = 1.80% K−1 (I519/I555, 298 K) via the FIR mode, and are SA = 661 × 10−4 K−1 (548 K) and SR = 9.77% K−1 (298 K) via the FL mode, which are higher than those of most previous studies.

Synthesis of Yb3+/Er3+ co-doped Ca9Gd2W4O24 crystals for use in optical thermometry

Ca9Gd2W4O24: Yb3+/Er3+ crystals were synthesized by solid state method. The structure, morphology, size and upconversion luminescence features had been characterized. These results indicated that Ca9Gd2W4O24 has a tetragonal cell and irregular blocky particle shapes. In upconversion, green (2H11/2, 4S3/2 → 4I15/2) and red (4F9/2 → 4I15/2) emissions were observed, both of which occurred via a two-photon populating process. Additionally, characteristics of the green UC emission were studied, including its temperature ranging from 298 K to 503 K and the sensitivity was 0.0075 K−1 at 473 K. This result indicated that Ca9Gd2W4O24: Yb3+/Er3+ crystals may have potential application in high temperature environment as safety sign.

Multifunctional optical thermometry using dual-mode green emission of CaZrO3:Er/Yb/Mo perovskite phosphors.

The weak emission intensity of rare-earth element-doped dual-mode materials leads to low-sensor sensitivity, which is a challenge in optical sensor applications. The present work achieved high-sensor sensitivity and high green color purity based on the intense green dual-mode emission of Er/Yb/Mo-doped CaZrO3 perovskite phosphors. Their structure, morphology, luminescent properties, and optical temperature sensing properties have been investigated in detail. Phosphor shows a uniform cubic morphology with an average size of approximately 1 μm. Rietveld refinement confirms the formation of single-phase orthorhombic CaZrO3. Under the excitation of 975 and 379 nm, the phosphor emits pure green up and down-conversion (UC and DC) emission at 525/546 nm corresponding to 2H11/2/4S3/2-4I15/2 transitions of Er3+ ions, respectively. Intense green UC emissions were achieved because of energy transfer (ET) from the high-energy excited state of Yb3+-MoO42- dimer to the 4F7/2 level of Er3+ ion. Furthermore, the decay kinetics of all obtained phosphors confirmed ET efficiency from Yb3+-MoO42- dimer to Er3+ ions, leading to strong green DC emission. Moreover, the DC of the obtained phosphor shows that a sensor sensitivity value of 0.697% K-1 at 303 K is higher than the UC (0.667% K-1 at 313 K) because the thermal effect generated by the DC excitation source light is ignored compared with UC luminescence. CaZrO3:Er-Yb-Mo phosphor shows intense green dual-mode emission with high green color purity, 96.50% of DC and 98% of UC emissions, and high sensitivity, making it suitable for optoelectronic devices and thermal sensor applications.

Enhanced bright green luminescence from GdOF:Ho3+ up-conversion phosphor via Yb3+ doping

In this paper, a series of GdOF-based green phosphors doped with Ho3+ and Yb3+ ions was prepared by a simple co-precipitation method. The crystal structures and optical properties were investigated in detail. The intensity of the emission of GdOF:Yb3+,Ho3+ phosphors is enhanced by the effective energy transfer from Yb3+ to Ho3+, and the optimal luminescence is achieved with the Ho3+ doping amount of 0.1 mol% as well as Yb3+ doping amount of 5 mol%. Tunable UC emission of samples is achieved by adjusting the doping concentration of Ho3+ or Yb3+. The purity of the green UC emission is further improved by enhancing the excitation pumping power. In addition, logarithmic functions of green, red and near-infrared radiation intensities were calculated versus logarithmic function of pump power for further study. A possible UC luminescence mechanism between Yb3+ and Ho3+ is discussed based on power-dependent UC luminescence spectrum and decay lifetimes. These results suggest that GdOF:Yb3+,Ho3+ phosphors with bright and high-purity green UC emission have potential applications in the fields of bioimaging, display and illumination.

Enhanced up-conversion luminescence of Tb3+-Yb3+ doped glass ceramics by doping Li+

Tb3+-Yb3+ co-doped transparent glass ceramics (GCs) containing Y2Ti2O7 crystal phases were synthesized by the melt crystallization. The light transmittance of GCs in the visible region reached 78%, and the average grain size was 278 nm under the optimal heat treatment conditions (720 °C/2 h). The GCs exhibited greater up-conversion luminescence intensity than precursor glass, and the reason for this result was explained in accordance with the Judd-Ofelt theory. Moreover, the introduction of Li+ did not change the crystalline phase of GCs. The emission intensity of the green light of the 8% Li + doped GCs was significantly enhanced by nearly 4.48 times under 980 nm excitation. The XRD refinement results suggest that the enhanced luminescence intensity is correlated with the change of the Y2Ti2O7 crystal lattice caused by Li+ doping. The relevant luminescence mechanism was elucidated. The results suggest that Li+ doped transparent GCs open novel avenues for green UC applications.

Optical fiber sensor based on upconversion luminescence for synchronous temperature and curvature sensing.

A multifunctional optical fiber sensor based upconversion luminescence (UCL) for synchronous temperature and curvature sensing was proposed. The sensor was fabricated by assembling UCL nanoparticles doped by rare earth (RE) ions in polydimethylsiloxane (PDMS) materials. Temperature measurements were achieved through the fluorescent intensity ratio (FIR) technique with the dual green UC luminescence generated. The fabricated sensor provided the temperature sensitivity of 714.82 K-1 with excellent linearity (R2=0.997) at a temperature range of 303 to 423 K. In the lower temperature region, temperature measurement based on the FIR technology is almost independent on the fluorescence intensity of a 525 nm emission peak. Hence, deformation produced by the sensor through bending results in detectable and reversible changes in its reflected light, allowing the curvature to be simultaneously measured. The sensor can monitor temperature and curvature simultaneously, providing a new optical alternative for multi-parameters monitoring in the future.

Thermometric sensing performance in Erbium modified SrBi2-xNb2ErxO9 ferroelectric ceramic for optoelectronic devices

Er3+ doped ferroelectric ceramic compositions SrBi2-xNb2ErxO9 (x = 0–5 mol %) are prepared by solid-state reaction method and sintered at 1000 °C. The ceramic's structural, ferroelectric, optical, and thermometric sensor properties have been studied. The XRD analysis confirmed the orthorhombic geometry and the A21am phase group of the ceramic. The FTIR studies revealed the typical modes (602 cm−1 and 802 cm−1) of the Aurivillius phases of bismuth layered structure ferroelectrics (BLSFs). The improved hysteresis loops are traced under the electric field < ± 50 kV/cm, and P-E parameters seem to be affected by the insertion of the Er3+ dopant. In upconversion luminescence (UCL) spectra, two intense green bands at 529 nm and 549 nm and a diminished red peak at 670 nm have been identified, corresponding to a 980 nm exciting wavelength. The increase in the lifetime with changing erbium content indicates the efficient energy transfer in Er3+ ions, which results in non-radiative transition at a higher doping level. The optimum dopant concentration is x = 0.03 and is used to measure the pump power dependence on the UCL emission intensity. This study suggests that the two photons are involved in green and red UC emissions. The maximum sensitivity achieved in SrBi2-xNb2ErxO9 ceramic at x = 0.03 is 0.0086 K−1 at 443 K, ranging between temperatures 303 K–443 K, making it a promising non-contact sensor material.

Effect of Synthesis Temperature on the Structure and Luminescence Properties of the NaAlSiO4:Er3+ Phosphors

We report the synthesis and the effect of synthesis temperature on the crystal structure and dual mode (DC/UC) luminescence properties of the NASE-1000–1300. Two different polymorphs, i.e., nepheline and carnegieite of the NASE have been prepared just by changing the annealing temperature. Multi wavelength excitation can be used to obtain different emissions in visible and NIR regions. Under 380 and 980 nm excitation, the NASE-1000–1300 produces 1535 nm NIR emission, whereas green and red visible emissions are observed with 980 and 808 nm laser excitations. Under 980 nm laser excitation, the synthesis temperature dependent nepheline and carnegieite polymorphs emit intense red and green emission, respectively. Two-photon process is responsible for the green and red UC emissions of the NASE-1300. The NASE-1000-1300 produces intense red emission under 808 nm laser excitation. We believe that the NASE-1000–1300 could be a promising candidate for the photonic as well as biological applications.

Optical thermometry and broad infrared luminescence in highly sensitized TBO glass

This work mainly reports the optical thermometry based on frequency upconversion and the infrared luminescence of Er3+-Yb3+ codoped TeO2-B2O3 (TBO) glasses prepared via melt-quenching technique. The amorphous nature of the prepared glass samples has been confirmed from the XRD analysis. FTIR analysis of the prepared glasses shows the existence of possible bands along with the phonon energy ∼670 cm−1. Judd-Ofelt analysis has been performed on the basis of absorption spectra and various radiative parameters calculated. The order of the intensity parameters (Ω6 > Ω2 > Ω4) indicates ionic nature of the Er-O bond which is further confirmed by the naphelauxetic ratio, covalency and bonding parameter. The enhancement of about 155 times and 327 times in the green and red UC emission intensity of the codoped glass as compared to the Er3+ doped TBO glass has been reported. The absorption cross-section around 980 nm in the codoped glass is found to be ∼43 times larger as compared to the 4I15/2 → 4I11/2 absorption transition in the Er3+ doped glass. The temperature sensing study of the codoped glass with high ‘Ω6’ value has been performed and low value of the absolute sensitivity has been explained on the basis of Judd-Ofelt parameters. The figure of merit for gain bandwidth (9216.81 × 10−27 cm3) & maximum gain coefficient (2.27 cm−1) corresponding to the infrared luminescence peaking at ∼1.5 μm and spectroscopic quality factor (0.28) have been evaluated.

Upconversion luminescence and temperature sensing characteristics of Ho3+/Yb3+ co-doped tellurite glasses

The upconversion emission spectra of Yb3+/Ho3+co-doped TeO2-ZnO-BaO glasses were studied for solid-state lighting and optical thermometry. The studied glasses were prepared using the melt quenching technique. The green and red UC emissions of Ho3+ions are due to two-photon absorptions, which cause the various energy transfer processes. The studied glasses show tunable color properties and high-temperature sensor sensitivity. Color coordinates on the CIE chromaticity diagram of those were affected by the pump power and shifted from green to red region at higher Ho3+concentrations. The 5F5 level and (3F4,5S2) levels of Ho3+ are found to be thermally coupled levels. The energy difference (ΔE) between these levels is calculated as 2463.66 cm−1. Among the studied glasses, Yb3+(3.0 mol%)/Ho3+(0.15 mol %) co-doped TeO2-ZnO-BaO show the highest absolute sensitivity of 0.011K−1 at 503K. In the light of conducted observations, the studied glasses are proposed as a good candidate material for lighting and optical temperature sensing.

Up-conversion luminescence and temperature sensing properties of Ho3+/Gd3+ co-doped YbNbO4 phosphors

Ho3+/Gd3+ co-doped YbNbO4 phosphors were successfully synthesized by the high-temperature solid-state method. The crystal structure, morphology structure, element distribution, up-conversion luminescence and relative optical temperature sensing properties were investigated. X-ray diffraction (XRD) and field emission-scanning electron microscopy (FE-SEM) analysis demonstrated that the doping of Ho3+/Gd3+ ions had no change in crystal structure and microstructure of YbNbO4 phosphors. Under the excitation of 980 nm laser radiation, the green and red UC emissions were achieved by prepared phosphors, corresponding to the transitions of (5F4, 5S2)→5I8, 5F5→5I8 of Ho3+ ions. It is observed that the UC luminescence intensity was significantly enhanced for Ho3+/Gd3+ co-doped YbNbO4 samples compared to the mere Ho3+ doped YbNbO4 sample. Moreover, Ho3+/Gd3+ co-doped YbNbO4 samples' temperature sensitivity ranging from 303 to 663 K was calculated based on the fluorescence intensity ratio (FIR) method. The maximum sensitivity reached 0.0078 K−1 at 663 K. These results indicate that the YbNbO4:Ho3+/Gd3+ samples are a promising candidate for optical temperature sensing and up-conversion luminescence.

Enhanced upconversion emissions of NaNbO3:Er3+/Yb3+ nanocrystals via Mg2+ ions doping

The rod-like NaNbO3:Er3+/Yb3+ nanocrystals codoped with Mg2+ ions were firstly synthesized by hydrothermal method. The effect of Mg2+ ions on the phase structure and morphology of NaNbO3:Er3+/Yb3+ was investigated by XRD and SEM spectra. Addition of Mg2+ ions enhanced the intensities of green and red UC emissions by about 3 times and prolonged the lifetime of the 4S3/2 → 4I15/2 transition of Er3+ ions. The pump power dependences were measured to understand the upconversion mechanism under 980 nm excitation. The tailored local environment of Er3+ ions by codoping Mg2+ ions was responsible for the improved optical characteristics of NaNbO3:Er3+/Yb3+/Mg2+ nanocrystals.

Broadband Cr3+-sensitized upconversion luminescence of LiScSi2O6:Cr3+/Er3+

Broadband sensitization is an effective strategy to enhance the upconversion luminescence (UCL) of lanthanide ions. Herein, novel UC materials LiScSi2O6:Cr3+/Er3+ (LSS:Cr3+/Er3+) were synthesized by high-temperature solid state reaction and their luminescent properties were investigated. LSS:Cr3+/Er3+ has the broadband absorption in the spectral range of 600–800 nm, and meanwhile shows green UC emissions of Er3+ upon pumping Cr3+ by the 690 nm laser. The UCL of LSS:Cr3+/Er3+ belongs to the two-photon process and is attributed to the energy transfer upconversion mechanism. The effects of the Cr3+ and Er3+ concentration as well as the Yb3+ introduction were also studied. LSS:Cr3+/Yb3+/Er3+ exhibits the interesting dual-mode UCL, capable of generating the UCL of Cr3+ upon pumping Yb3+ ions and the UCL of Er3+ upon pumping Cr3+ ions. This research might promote the development of novel broadband Cr3+-sensitized UC materials.

Investigation of upconversion luminescence for Tb3+/Yb3+ co-doped CaLnAlO4 (Ln = Y, Gd, La) phosphors

Tb3+/Yb3+ co-doped CaGdAlO4 phosphors were synthesized by a conventional solid-state reaction method. Green UC emission was obtained from the prepared samples under 980 nm excitation via a cooperative energy transfer process. The cooperative energy transfer efficiency from Yb3+ to Tb3+ and the phonon-assisted energy transfer efficiency from Tb3+ to Yb3+ were evaluated to be ~40% and ~1%, respectively. Partial substitution of Gd3+ ions with Y3+ or La3+ ions leads to an increase of UC intensity due to the enhancement of local distortion. The results indicate that the synthesized phosphors may be used to increase the efficiency of perovskite-based photovoltaic cells excited by green light.

Full-color up-conversion emission from the molybdate of Yb1.98Ln0.02Mo4O15 (Ln=Er, Ho, Tm)

Here we report the realization of full-color up-conversion emission in the novel host matrix of Yb2Mo4O15 at 980 nm excitation. The high concentration of Yb3+ ions in the host allows us to achieve highly efficient UC luminescence due to the improvements of both absorption efficiency of excitation energy and energy transfers from Yb3+ to activator ions. By selecting the activator ions of Ho3+, Er3+ and Tm3+, three primary color of red, green and blue (RGB) with high color purity are obtained, respectively. Moreover, stable and pure white emission (0.3380, 0.3382) are achieved by blending the three primary color phosphors in appropriate proportions. And the color cast is completely avoided due to the same density and particle size distributions of the three phosphors of Yb2Mo4O15:0.02Ln3+ (Ln = Er, Ho, Tm). By further mixing them with the nail polish, the mixtures show bright green, red and blue UC emissions, which demonstrate their promising applications in the multiple anti-counterfeiting.