Energy Level Transition Research Articles

Synthesis, structural characterizations and theoretical calculations of the Ni(II) complex based on a novel Salamo-Salen-Salamo-type hybrid ligand

The Salen compound is a typical Schiff base ligand, and by combining one Salen-structure unit with two Salamo-structure units, a novel hybrid Salamo-Salen-Salamo-type ligand H4L was synthesized. The synthesis of corresponding complexes based on the hybrid ligand was studied. Ni(II) ion participates in coordination and synthesizes a hybrid Salamo-Salen-Salamo-type mononuclear complex [Ni(LH2)]. X-ray single crystal diffraction analysis showed that Ni(II) ion has coordinated with Salen N2O2 structure, forming a planar geometry with tetracoordination. The Salamo structure units are not involved in coordination, and two Salamo long chains are spatially close to each other and there are N, O atoms that are easy to coordinate with metals, forming a potential coordination environment. The spectral properties of the complex was further discussed by IR and UV-vis spectroscopy, and the binding ratio of the ligand H4L to Ni(II) ion in solution was verified by UV-vis titration spectroscopy. Through the structural optimization of the ligand and single-point energy calculation of the complex, the HOMO-LUMO gaps of the ligand and the complex were analyzed to determine the softness of the ligand and the complex. TD-DFT analysis of the ligand and its complex was found to be consistent with experimental results, and the energy level transition sources of the main absorption peaks and their contributions were analyzed. The interaction force within the molecule of the Ni(II) complex was calculated, and finally the movable free region of the complex molecule in the unit cell was calculated and displayed.

Improved 2∼5 μm mid-infrared fluorescence through energy transfer processes in Er3+/Ho3+ co-doped fluoride glasses

In this paper, Er3+/Ho3+ co-doped fluoride glasses were prepared by the high temperature melt-quenching technique. Pumped by the 980 nm LD, as a result of the emission spectra overlapping of Er3+ and Ho3+ ions, a broadband mid-infrared emission band from 2530 to 2950 nm with a full width at half maximum of the synthetic fluoride glasses near 231 nm was obtained, which exist latent application in wide band tunable mid-infrared fiber laser. Furthermore, the intense 4.1 μm mid-infrared fluorescence (3600–4400 nm) was obtained and the FWHM was 320 nm. The up-conversion emission peaks around 525, 546 and 660 nm, near-infrared emissions at 1.2 and 1.5 μm together with mid-infrared fluorescence around 2.0 μm was observed in Er3+/Ho3+ co-doped fluoride glass. Moreover, the relevant energy transfer processes were discussed in detail based on the emission spectrum and the energy level transition processes. The results indicate that the fabricated Er3+/Ho3+ co-doped fluoride glasses exist prominent emission features for fiber laser gain medium.

Temperature/laser dependence of N3 optical centers in natural type Ia diamonds through photoluminescence spectroscopy

In this work, low-temperature photoluminescence spectroscopy was employed to investigate the N3 optical color center in natural type Ia diamond. The optical properties of the N3 center with regular changes in testing temperature and laser power were studied, and the energy level transition was also discussed. The results showed that the PL intensity of the N3 center enhanced sub-linearly with laser power increased, indicating that the electron transition of the N3 center was mainly radiative recombination with weak Auger recombination participation. In addition, the physical model was employed to analyze the change in the zero phonon line with the increase in the test temperature; it obtained thermal quenching activation energy (25.2 meV), bond softening, and strong interaction with acoustical phonons of the N3 center. The theoretical analysis of the broadening parameters revealed that the longitudinal optical phonon energy was 55.1 meV, and the electron–optic phonon coupling strength was 2.3 meV.

Multiresponsive Self-Healing Lanthanide Fluorescent Hydrogel for Smart Textiles.

Lanthanide organometallic complexes exhibit strong luminescence characteristics, owing to their antenna effects. The f-d energy level transition causes this phenomenon, which occurs when ligands and the external electrons of lanthanide metals coordinate. Based on this phenomenon, we used two lanthanide metals, europium (Eu) and terbium (Tb), in the present study as the metal center for iminodiacetic acid ligands. Further, we developed the resulting fluorescent organometallic complex as a smart material. The ligand-metal bond in the material functioned as a metal chelating agent and a cross-linking agent in a dynamically coordinated form, thereby prompting the material to self-heal. Temperature-sensitive poly-N-isopropylacrylamide was incorporated into the material as the polymer backbone. Afterward, we combined it with water-soluble poly(vinyl alcohol) and an additional ligand from poly(acrylic acid) to fabricate a high-performance hydrogel composite material. The shrinkage and expansion of the polymer form a grid between the materials. Because of the different coordination stabilities of Eu3+ and Tb3+, the corresponding material exhibits environmental responses toward excitation wavelength, temperature, and pH, thus generating different colors. When used in fabrics, the cross-linking mechanism of the material effectively looped the material between fabric fibers; furthermore, the temperature sensitivity of the polymer adjusted the size of pores between fabric fibers. At relatively higher temperatures (>32 °C), the polymer structure shrank, fiber pores expanded, and air permeability improved. Thus, this material appears to be promising for use in smart textiles.

Fluorescence properties and thermal stability of Sr2Gd1-xNbO6: xEu3+ with dual-wavelength excitation response

A series of double perovskite-type Sr2Gd1-xNbO6: xEu3+ (x = 0.04–0.12) red-emitting phosphors were successfully synthesized by a solid-state high-temperature sintering reaction, and the microstructure and luminescent performance of the phosphor are investigated in detail. The red-emitting phosphor has a monoclinic crystal structure with a space group of P21/c. The optimal concentration of the Eu3+ dopant in the Sr2GdNbO6 host was 0.08. Under dual-wavelength excitation of λex = 468 nm and λex = 395 nm, phosphor emits a red-orange color, and the principal emission peaks are located at 622 nm and 593 nm, which correspond to the 5D0→7F2 and 5D0→7F1 energy level transitions of Eu3+, respectively. Under the excitation of blue light λex = 468 nm, the phosphor exhibits not only a greater thermal stability but also a high luminescence color purity (93%). It is a new potentially red-emitting phosphor with dual wavelength excitation responsiveness.

Experimental and Semiclassical Stark Widths and Shifts for Spectral Lines of Neutral and Ionized Atoms (A Critical Review of Experimental and Semiclassical Data for the Period 2008 Through 2020)

This Review Article compares new experimental and corresponding semiclassical Stark broadened data for non-hydrogenic spectral lines of neutral atoms and positive ions. This Review covers the period 2008 until the end of 2020 and presents the continuation of previous critical reviews from 1976 (two), 1984 (two), 1990, 2002, and one from 2009. This Review reports the Stark broadening parameters of 1665 spectral lines belonging to 35 elements with 61 different atomic and ion species. The data are taken from 60 papers. Experimental data are arranged by elements and spectra, and these are reported in tables in alphabetical and numerical order, respectively. Each experimental Stark broadening parameter is followed with estimated accuracy. The experimental Stark broadening and shift data presented in the tables are compared with the corresponding semiclassical results available in the literature. In addition, for comparison experiments versus semiclassical theoretical Stark broadening parameters, a numerically improved theoretical approach developed based on Griem and co-workers’ theory is used to evaluate Stark widths and shifts of all studied lines whenever required atomic energy levels data and transition probabilities are available. At the end of the text report, for each analyzed neutral or ion species, the information about the location of the same species data in preceding reviews is given.

Study on preparation, optical properties and mechanism of Zn2SnO4:Cr3+ with high NIR luminescence intensity

In this work, Zn2SnO4:xCr3+ with high near-infrared luminescence intensity (broad emission centered at 800 nm and sharp emission at 703 nm) were successfully prepared by high temperature solid state method. Measurements indicated that the samples exhibited obvious photoluminescence as well as persistent luminescence properties. The results of X-ray diffraction indicated that high temperature facilitated the entry of Cr3+ into the Zn2SnO4 crystal lattice and formed replacement doping and promoted the luminescence efficiency of the samples. And, under the condition of 1450 °C and 0.002 at% Cr3+ concentration, sample with optimum NIR fluorescence properties was prepared. In the high-temperature sintering process, many defects of Zn2SnO4 were generated, which effectively promoted the formation of vacancies. The energy levels of these lattice defects (trap energy levels) facilitated the sub-stable trapping of electrons and produce afterglow properties. Analysis of luminescence mechanism reveals that the broad emission band centered at 800 nm and the sharp emission peak at 703 nm were derived from the energy level transitions of 4T2(4F)→4A2 and 2E→4A2 of Cr3+, respectively. Though, the long afterglow luminescence duration of Zn2SnO4:Cr3+ needs to be further improved compared with gallate-based NIR phosphors, Zn2SnO4:Cr3+ do have a promising application in bio-imaging due to its special NIR emission range.

PH-controlled construction of 2D and 3D micro-nano hybrid carbon architectures with fluorescence/phosphorescence dual-mode emission for white-emitting diodes

Developing nanocarbon-based white-emitting diodes (WLEDs) with high energy conversion efficiency is still extremely challenging due to the issue of Kasha's rule and serious self-aggregation caused luminescent quenching of nanocarbon in a solid-state. Herein, the synergistic strategy of framework and intercalator between nanosheets and carbon dots (CDs) was adopted. Three novel 2D nanosheets, 3D nanoflowers and 3D parasa consocia-like micro-nano carbon architectures decorated with dispersive CDs were successfully fabricated through one-step hydrothermal reaction at different pH medium. The pH-regulated mechanisms of morphology and structure, via degree modulation of condensation and carbonization, were further proposed. All samples exhibited bright white emission, derived from fluorescence/phosphorescence dual-mode emission. The hybrid emission made sufficient utilization of single and triplet excitons with the quantum yield of 16%–30%. The superior white light with CIE coordinates of (0.331,0.334) was recorded for neutral sample (p-CNDs-N), ascribed to the multiple energy level transitions from polydisperse luminescence centers. The luminous efficiency was remarkably improved in HCl (p-CNDs-H) and NaOH treated samples (p-CNDs-OH), resulting from inner carbonization, external cross-linked network and the passivation of surface defect sites. This is the first example for pH-controlled fabrication of multi-dimension hybrid nanocarbon structures and pH-controlled fluorescence/phosphorescence dual-mode emission for highly efficient carbon-based WLEDs.

Effective ratiometric optical thermometry based on inverse temperature dependent dual near infrared emission of Cr3+ doped BaAl4Sb2O12 phosphor

The device of reliable non-contact ratiometric optical thermometry technique gradually became a cutting-edge research pot over decades due to its intriguing features of rapid response, high accuracy and simple operation. In which, Boltzmann-based optical thermometry has attracted widespread attention for its exceptional reliability. Here in, we put forward an effective ratiometric optical thermometry based on the highly sensitive and effective Boltzmann-based 2E→4A2/4T2→4A2 emission ratio of BaAl3.9Sb2O12:0.1Cr3+. The phosphor shows dual near-infrared luminescence lines at 698 nm and 710 nm (2E→4A2) and the luminescence band near 750 nm (4T2→4A2). With the temperature elevating from 170 to 470 K, the emission intensity of luminescence lines undergoes continuous enhancement and possess excellent anti-thermal quenching property (3.5-fold at 470 K, compared to 170 K). In contrast, the emission intensity of luminescence band shows a monotonic decline trend. The luminescence intensity ratio shows a good linear relationship in the Arrhenius diagram, and the relative sensitivity reaches 2.08 % K−1 at 170 K, which corroborates the BaAl3.9Sb2O12:0.1Cr3+ has the potential as the optical cryogenic thermometer. In the end, the work provides some insights into the development of novel Cr3+-doped thermometry materials based on the 2E and 4T2 energy level transitions in intermediate crystal field environments.

Spatial Spectral Characteristics of Partial Discharge with Different Electrode Models

In this paper, the spatial spectral characteristics of partial discharge (PD) under different electrode models are mainly studied. In the initial corona discharge stage, the emission spectrum is mainly emitted by the N2(C3IIu→B3IIg) energy level transition of the N2 second positive band system. The spectrum is in the ultraviolet range of 294–436 nm, and its main peak is at 337 nm. The streamer discharge stage spectrum is mainly emitted by the energy level transition of the second positive band system of N2, N+, NO, and O+ and the first positive band system of N2(B3IIg→A3Σu+). In the gap of different polarity electrodes, the ultraviolet spectrum content near the positive polarity is more abundant. The UV spectra ranges are 202–225 nm and 229–292 nm, respectively. The discharge of the needle–sphere system is more intense in visible light and near-infrared light, with peaks at 500 nm and 777 nm, respectively. In addition, the PD process based on the finite element method is simulated by COMSOL Multiphysics software. The simulation results show that the distribution of high-energy electron density varies with the electrode spacing and discharge model. The influence of particle energy level transition on the spatial spectral characteristics of PD is verified. This work provides important insights and possibilities for future fluorescent fiberoptic sensing and positioning for spatial PD detection and positioning using spectral characteristic peaks as detection quantities or excitations.

Effect of Nb2O5 on the ∼2.0 μm band luminescence of Ho3+/Tm3+/Ce3+ tri-doped tellurite glass

In this work, the effect of Nb2O5 oxide on the ∼2.0 μm band luminescence of Ho3+/Tm3+/Ce3+ tri-doped tellurite glass with composition of TeO2–ZnO–La2O3 was studied. The doped tellurite glass was synthesized by using the melt-quenching method. Under the pumping of 808 nm laser diode (LD), a broad and relatively flat fluorescence emission ranging from 1600 to 2200 nm with a full width at half maximum (FWHM) of 374 nm was obtained by optimizing the concentration combination of Ho3+, Tm3+ and Ce3+ ions. The observed broad luminescence was attributed to the spectral overlapping between the energy level transitions from 3F4 to 3H6 of Tm3+ at 1.82 μm and that from 5I7 to 5I8 of Ho3+ at 2.0 μm. Further, an increment by about 143% in peak intensity of 1600∼2200 nm broad luminescence was found after the introduction of Nb2O5 oxide, which is due to the enhanced energy transfer from Tm3+ to Ho3+ ions, and the increased multi-phonon relaxation (MPR) rate from higher levels to fluorescence emitting levels. It can be inferred from the results that a potential gain medium suitable for applications in optoelectronic devices operating at ∼2.0 μm band can be produced by incorporating an appropriate amount of Nb2O5 oxide into Ho3+/Tm3+/Ce3+ tri-doped tellurite glass.

Structural, optical, elemental and photometric properties of Sm3+ activated Ca3Ga4O9 oxide phosphors for WLEDs

Solid-state lighting systems rely on the exceptional characteristics of phosphor-converted LEDs, including long lifetime, low energy consumption, and high brightness. This study focuses on the synthesis of Sm3+ activated Ca3Ga4O9 (CGO: Sm3+) orange-red emitting oxide phosphors using the solid-state reaction method. X-ray photoelectron spectroscopy was used to analyze the nature of bonding with the dopant ion and oxidative states of the elements in the structure. Scanning electron microscopy and energy dispersive spectroscopy revealed agglomerated particles with a flake-like structure in the Sm3+ doped sample. The optical properties of the samples were investigated using UV-Visible diffuse reflectance and photoluminescence excitation and emission analyses. The Sm3+ doped samples showed maximum excitation at 404 nm and 479 nm, with corresponding energy level transitions of 6H5/2 - 6P3/2 and 6H5/2 - 4I11/2, respectively. Emission spectra exhibited four emission maxima at 564, 601, 645, and 708 nm, representing the 4G5/2 - 6H5/2, 4G5/2-6H7/2, 4G5/2-6H9/2, and 4G5/2-6H11/2 transitions of Sm3+ ions. The Kubelka-Munk function was used to calculate the optical energy gap values. Photometric parameters, including color coordinates, correlated color temperature, and color purity, were determined. The CIE chromaticity coordinates of CGO: Sm3+ were found in the orange-red region, indicating its potential as a promising candidate for use in phosphor-converted white LEDs applications. The study concludes that Sm3+ activated CGO phosphors have great potential for use in solid-state lighting systems.

Machine Learning Accelerated Study of Defect Energy Levels in Perovskites

Manipulating the defect tolerance is one of the effective ways to maintain the high power conversion efficiency and keep the stability of perovskite semiconductor materials. So, rapid screening for defects and trap states in the perovskite semiconductor candidates is urgently needed. Theoretical investigations of defects based on density functional theory (DFT) are still limited by their extremely high consumption of computational resources and time. We implement an accelerated material discovery approach using artificial intelligence and DFT, which can predict the defect transition levels in the candidate perovskite semiconductor materials. To verify the accuracy of our models, Cs3Sb2Br9 and Cs2SnBr6, which are out of the dataset that we used in machine learning (ML) model construction, are taken as examples. The extrapolation of ML prediction models and the results given by DFT calculations are compared for defect transition energy levels. The two methods are consistent with each other with very small errors. Our strategy avoids complex and time-consuming computational work based on DFT and provides quick and efficient screening of physical properties with low cost.

The Laboratory Astrophysics Programme at Imperial College London

Advancements in ground- and space-based telescopes have resulted in an acute need for and improvement in the breadth and accuracy of the atomic data vital for the analysis of astronomical spectra. Many data, even for astrophysically important elements such as the iron group, have analyses dating back over 50 years, which are no longer suitable for the interpretation of modern, high-resolution astrophysical spectra. The Imperial College Spectroscopy group is addressing this need by measuring new atomic data and improving the accuracy of existing data using Fourier transform spectroscopy from the infrared to the vacuum ultraviolet. Analysis of these high-resolution spectra has led to new and improved atomic data for a wide range of astrophysically important elements. Reductions in uncertainties of transition wavelengths and energy levels are routinely over an order of magnitude and transition probabilities are measured to a few percent of uncertainty. Our work has increased both the quantity and quality of available atomic data. In this paper, we provide an update of our recent investigations and research plans. We also detail the improvements being made to our world-class laboratory to ensure we are able to meet the future data needs of the astrophysical community.Graphical abstract

Local crystal field-induced tunable mid-infrared luminescence of CsPb1-xErxBr3 perovskite fluoride glasses and applied to the detection of CO2 in hydrogen energy

In recent years, the mid-infrared (MIR) source has become important for a wide range of applications in sensing, spectroscopy, imaging and communications. Due to the unique intra-4f shell transition, the infrared luminescence of rare earth ions has been widely used in infrared light-emitting devices. Despite recent advances with mid-infrared gain platforms, the lack of a tunable mid-infrared luminescence mechanism remains a significant technological challenge. Here, an efficient mechanism for tuning the local crystal field of rare earth ions by modifying the crystal structure of rare earth perovskites is revealed and tunable mid-infrared luminescence of rare earth ions is achieved. Significantly, the local crystal field of Er3+ is tuned by changing the crystal structure of the CsPb1-xErxBr3 rare earth perovskite. The energy level transition (1550 nm: 4I13/2 → 4I15/2 and 2.7 μm: 4I11/2 → 4I13/2) is changed by tuning the asymmetry of the crystal field and the FWHM of the mid-infrared emission is tunable from 80 nm to 130 nm. A convenient, highly accurate device has also been developed that can be used to measure the CO2 concentration in hydrogen energy. The perovskite glass infrared light source has been well adapted to the characteristic infrared absorption peak of CO2. The instrument can monitor the CO2 concentration in real time, avoiding the safety risks associated with the use of electronic instruments in hydrogen energy. These results are expected to open a wide avenue for a new type of tunable mid-infrared luminescence for a wide range of applications.

Up and down-conversion photoluminescence energy demonstration of Ho3+/Yb3+ co-doped double perovskites microcrystals

Recently, lanthanide-doped fluorescence materials with perovskite structures have attracted great attention due to their abundant 4f energy levels, of which up- and down-conversion photoluminescence (PL) usually can be achieved by energy-level transition of single or multiple rare-earth ions (REI). Here, we synthesized for the first time a series of holmium (Ho) and ytterbium (Yb) co-doped Cs2Ag0.4Na0.6In0.9Bi0.1Cl6 (CANIBC) microcrystals (MCs) by hydrothermal method and realized the synergistic effect of efficient dual-mode PL of host and REI. The CANIBC MCs show yellow-white light emission stimulated by a 405 nm laser, of which the down-conversion (DC) PL is superimposed by the self-trapped excitons (STEs) emission of [AgCl6]5- octahedral and the energy level leap emission of REI. While the green emission of Ho3+ can be observed on the up-conversion (UC) PL stimulated by a 980 nm laser. We systematically analyzed the effect of CANIBC MCs in the dual-mode PL by time-resolved spectroscopy and found the existence of energy transfer between the STEs to REI in the DC PL process. Whereas in UC PL there is only energy transfer between REI. The variable-temperature dual-mode PL, reflects good temperature measurement performance. Simultaneously, it is effectively processed into a powder and mixed with 415 nm chips to create warm white light-emitting diodes with a CIE of (0.34, 0.36).

Triboelectrification Catalytic Degradation of Organic Pollutants in Water Environment

With the rapid development of industrialization, more and more organic pollutants are entering the water environment, rendering the treatment of organic pollutants a key issue in protecting it. Therefore, finding a convenient and effective method for degrading organic pollutants in water is of great importance. Triboelectrification is known as the process of charge transfer during the friction process. It is always accompanied by the energy level transition of electrons or holes, making it a potential method for catalytic degradation, which we refer to as triboelectrification catalysis. In this study, a set of experimental equipment was developed. The device is composed of a mechanical system, a control system, and a measurement system that can realize the quantitative measurement of the triboelectrification catalysis under different friction pairs, different loads, and different contact frequencies. Using the developed device, we observed stable triboelectrification catalytic degradation. This study performed triboelectrification catalytic experiments on various organic compounds including methyl orange, rhodamine, and tetracycline. The results revealed that these three organic compounds were degraded by 39%, 15%, and 20%, respectively, within three hours of being under the influence of triboelectrification catalysis. Subsequently, this study conducted triboelectrification catalytic experiments using materials with different triboelectric capacities. This study found that the triboelectric capacity significantly impacted the triboelectrification catalytic degradation rate, providing further evidence for the mechanism of triboelectrification catalysis. Additionally, this study found that SiO2 and Al2O3, which also utilize electrons as the primary carrier for triboelectrification, are capable of catalyzing the degradation of a methyl orange solution. Therefore, this study suggests that the triboelectrification catalysis is a versatile and widely applicable method for treating organic pollutants in water. With a broad range of catalyst sources and the ability to effectively degrade various organic pollutants, it shows promise as a solution for the problem of water pollution.

Electrospun green-emitting La2O2CO3:Tb3+ nanofibers and La2O2CO3:Tb3+/Eu3+ nanofibers with white-light emission and color-tuned photoluminescence

Color-tuned luminescence and white-light emission materials have attracted much attention owing to their broad application prospects. Generally, Tb3+ and Eu3+ co-doped phosphors have color-tuned luminescence, but white-light emission is rarely achieved. In this work, color-tunable photoluminescence and white light emission are achieved in Tb3+ and Tb3+/Eu3+ doped monoclinic-phase La2O2CO3 one-dimensional (1D) nanofibers synthesized by electrospinning united with succedent strictly controlling calcination procedure. The prepared samples own excellent fibrous morphology. La2O2CO3:Tb3+ nanofibers are the superior green-emitting phosphors. To obtain 1D nanomaterials with color-tunable fluorescence, particularly those with white-light emission, Eu3+ ions are further selected and doped into La2O2CO3:Tb3+ nanofibers to obtain La2O2CO3:Tb3+/Eu3+ 1D nanofibers. The major emission peaks of La2O2CO3:Tb3+/Eu3+ nanofibers at 487, 543, 596 and 616 nm are attributed to 5D4→7F6 (Tb3+), 5D4→7F5 (Tb3+), 5D0→7F1 (Eu3+) and 5D0→7F2 (Eu3+) energy levels transitions under 250-nm (for Tb3+ doping) and 274-nm (for Eu3+ doping) UV light excitation, respectively. At different wavelengths excitation, La2O2CO3:Tb3+/Eu3+ nanofibers with excellent stability achieve color-tuned fluorescence and white-light emission with the help of energy transfer from Tb3+ to Eu3+ and tuning the doping concentration of Eu3+ ions. Formative mechanism and fabrication technique of La2O2CO3:Tb3+/Eu3+ nanofibers are advanced. The design concept and manufacturing technique developed in this work may offer fresh insights for synthesizing other 1D nanofibers doped with rare earth ions to tune emitting fluorescent colors.

Multiphoton absorption properties and bioimaging of solvent coligand cyclometalated Pt(II) complex

As a cyclometalated complex, solvent coligand Pt(II) complex with multiphoton absorption has been designed and synthesized. After the optical properties of the Pt(II) complex were studied carefully, time-dependent density functional theory calculation (TD-DFT) was used to further identify the triplet charge transitions of the complex. The specific energy levels of frontier molecular orbitals and the data related to the energy level transition showed that the Pt(II) complex had photoluminescent properties, and their phosphorescence emission originated from 3LLCT/3MLCT. Because of nonlinear optics (NLO) response, the Pt(II) complex could act as multiphoton absorption materials for bioimaging and anticancer application.

Synthesis, Crystal Structure and Photoluminescent Properties of Red-Emitting CaAl4O7:Cr3+ Nanocrystalline Phosphor

Calcium dialuminate, CaAl4O7, nanopowders with a grossite-type structure, doped with chromium ions, were synthesized via the combined sol–gel solution combustion method. The evolution of phase composition, crystal structure, and microstructural parameters of the nanocrystalline materials depending on the temperature of the thermal treatment was investigated via X-ray powder diffraction and applying the Rietveld refinement technique. The photoluminescent properties of CaAl4O7 nanophosphors activated with Cr3+ ions were studied over the temperature range of 4.5–325 K. The samples show deep red and near-infrared luminescence due to the 2E → 4A2 and 4T2 → 4A2 energy level transitions of Cr3+ ions under excitation in the two broad emission bands in the visible spectral region. The R lines emission reveals a strong temperature dependence. The feasibility of the material for non-contact luminescence sensing is investigated, and good sensitivity is obtained based on the (R2/R1) luminescence intensity ratio and the lifetime of the emission.