Red Emission Research Articles

Emission color tuning and enhancement of the upconversion emission in NaBiF4:Yb3+,Er3+ phosphors by controlling the Na/F ratio

NaBiF4:Yb3+(20 mol%),Er3+(2mol%) phosphors (NBF:Yb,Er) were synthesized by a simple precipitation method. Several NBF:Yb,Er samples were made with different Na/F ratios (from 2/16 to 6/16 and 6/24). XRD and SEM measurements indicated that all the NBF:Yb,Er phosphors presented an hexagonal phase and morphology of microbars with sizes of 1–2 μm, respectively. According to the photoluminescence measurements, these phosphors emitted red/green emission bands at 541/655 nm and their emission intensity increased ⁓10.5 and 21 times for the green and red bands, respectively, after increasing the Na/F ratio from 2/16 to 4/16. In addition, the emission color was tuned from deep-green to yellow. Moreover, the Na/F ratio was decreased from 6/16 to 6/24, this in turn, changed the color emission from deep-green to orange. This last change of color occurred because the red emission was mainly favored by the following two cross relaxation (CR) processes CR1: 4I11/2 (Er3+)+ 4F7/2 (Er3+)→4F9/2 (Er3+)+ 4F9/2 (Er3+) and CR2: 4S3/2 (Er3+)+ 2F7/2 (Yb3+)→4I13/2 (Er3+)+ 2F5/2 (Yb3+). The second CR2 process also promoted the NIR emission at 1527 nm. Additionally, the lifetimes for the green and red bands increased from 393 to 420 μs and from 428 to 518 μs with the Na/F ratio, respectively. Thus, we presented here a new strategy to enhance the photoluminescence intensity and to control the emission-color/lifetimes without using extra co-dopants (as previously reported in literature).

N,C,N-Pincers in Platinum Bimetallic Complexes: Influence of the Pincer and Bridging Ligands on the Metal-Metal Bond and the Photophysical Properties.

Precursors PtCl{κ3-N,C,N-[py-C6HMe2-py]} (1), PtCl{κ3-N,C,N-[py-O-C6H3-O-py]} (2), Pt(OH){κ3-N,C,N-[py-C6HMe2-py]} (3), and Pt(OH){κ3-N,C,N-[py-O-C6H3-O-py]} (4) were used to prepare d8-platinum bimetallic complexes. Precursors 1 and 2 react with AgBF4 and 7-azaindole (Haz) to give [Pt{κ3-N,C,N-[py-C6HMe2-py]}{κ1-N-[Haz]}]BF4 (5) and [Pt{κ3-N,C,N-[py-O-C6H3-O-py]}{κ1-N-[Haz]}]BF4 (6) and 3 and 4 with indolo[2,3-b]indole (H2ii) to generate Pt{κ1-N-[Hii]}{κ3-N,C,N-[py-C6HMe2-py]} (7) and Pt{κ1-N-[Hii]}{κ3-N,C,N-[py-O-C6H3-O-py]} (8). Subsequent addition of 3 and 4 to 5-7 affords bimetallic derivatives [{Pt[κ3-N,C,N-(py-C6HMe2-py)]}2{μ-N,N-[az]}]BF4 (9), [{Pt[κ3-N,C,N-(py-O-C6H3-O-py)]}2{μ-N,N-[az]}]BF4 (10), and {Pt[κ3-N,C,N-(py-C6HMe2-py)]}2{μ-N,N-[ii]} (11). X-ray structures of 9-11 reveal separations between the metals in sequence 9 (3.0515(4) Å) < 10 (3.2689(9) Å) < 11 (3.2949(2) Å). DFT calculations support σ overlap of the dz2 orbitals of platinum atoms, for 9 and 10. Accordingly, their absorption spectra show a MMLCT transition. Complex 9 is a red emitter. The excited state has 3MMLCT characteristics and a Pt-Pt separation of 2.763 Å. Complex 11 is a dual emitter in the red and NIR regions, in solid. Both excited states have a 3LC/LMCT characteristic and platinum-platinum separations of 3.290 and 3.202 Å. Intermediate 5 is a green emitter that achieves quantum yields close to unity, when diluted in PMMA and 1,2-dichloroethane at low concentrations.

Hexagonal rod-like Eu3+doped CaMoO4 phosphors: Structural, photoluminescence and photometric properties for display device applications

A multicolored LED illumination device is a compact, durable, easy to obtain color-adjustable output illumination source. It is frequently utilized in the domains of room illumination and exterior displays. However, the advancement of multicolor LEDs has been hampered by the rise in price and the fall in luminous efficacy while changing illumination colors. In the present investigation we have prepared intense red emitting Eu3+ doped CaMoO4 phosphor nanopowders via simple solid-state reaction technique. The powder X-ray diffraction (PXRD) studies reveal the crystalline nature of the samples with scheelite–type mono phase tetragonal structure with I41/a space group. The band gap (Eg) energy values were estimated and found to range between 4.63–5.32 eV. Scanning electron microscopy (SEM) studies reveled the hexagonal rod-like structures with different Aloe Vera gel concentrations. The particle size was found to be around 40 nm. The vibrational modes of the prepared powders were evaluated by using Fourier Transform Infrared Spectroscopy (FTIR) and Raman spectroscopy. It was observed from the results that, there were 26 vibrational modes of CaMoO4 (Γ=3Ag + 5Au + 5Bg + 3Bu + 5Eg + 5Eu) 8 of which (4Au and 4Eu) were infrared active and 13 (Ag, Bg, and Eg) are Raman active. Photoluminescence (PL) emission intensity increases up to 5 mol% of Eu3+ ions load and subsequently it declines due to the concentration quenching phenomenon and effective energy transfer from Mo-O charge transfer band (CTB) to 5D0 levels of Eu3+. It was noticed from PL emission spectra that, four intense peaks located at 5D0 → 7F1 (590 nm), 5D0 → 7F2 (613 nm), 5D0 → 7F3 (654 nm), 5D0 → 7F4 (702 nm) of Eu3+ respectively. The Commission International de I'Eclairage (CIE) diagram indicates the red color emission and average correlated color temperature (CCT) value was found to be 2050 K. Further, the external quantum efficiency (QE) and color purity (CP) were calculated to check the phosphor efficiency and found to be 92% and 72% respectively. The present investigation opens up a new avenue in the fabrication of low-cost display devices with high color purity and luminous efficacy.

Phosphorescent PdII-PdII Emitter-Based Red OLEDs with an EQEmax of 20.52.

Three dinuclear Pd(II) complexes (1, 2, and 3) with intense red phosphorescence at room temperature are here synthesized using strong ligand field strength compounds. All three complexes are characterized by nuclear magnetic resonance, high-resolution mass spectrometry, and elemental analyses. Complexes 2 and 3 are characterized by single-crystal X-ray diffraction. The crystalline data of 2 and 3 reveal complex double-layer structures, with Pd-Pd distances of 2.8690(9) Å and 2.8584(17) Å, respectively. Furthermore, complexes 1, 2, and 3 show phosphorescence at room temperature in their solid states at the wavelengths of 678, 601, and 672nm, respectively. In addition, they show phosphorescence at 634, 635, and 582nm, respectively, in the 2wt.% (PMMA) films, and phosphorescence at 670, 675, and 589nm, respectively, in the deoxygenated CH2Cl2 solutions. Among three complexes, complex 1 shows red emission at 634nm with phosphorescent quantum yield Ф = 67% in the 2wt.% PMMA film. Furthermore, complex 1-based organic light-emitting diode is fabricated using a vapor-phase deposition process, and their maximum external quantum efficiency reaches 20.52%, which is the highest percentage obtained by using the dinuclear Pd(II) complex triplet emitters with the CIE coordinates of (0.62, 0.38).

Synthesis of Cu2+ doped ZnO@ZnCdS thin film: Optical and electrochemical characterization

Doping strategies modify the optical and electrochemical characteristics of materials. In this research, we investigated the impact of Cu2⁺ doping in ZnO@ZnCdS nanocomposites synthesized via the co-precipitation approach. A comprehensive analysis was conducted on the structural, morphological, optical, and electrochemical features of the samples using various techniques, including scanning electron microscopy (SEM), atomic force microscopy (AFM), Energy Dispersive X-ray analysis (EDX), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), UV–Visible absorption, and photoluminescence (PL). Notably, Cu2⁺ doping induces changes in morphology, crystal size, absorption spectra, and band gap energy. Surface investigations reveal a flower-like structure, while XRD analysis indicates an increase in crystal size from 25.5 to 35.2 in thin films with copper content. The absorption spectra of UV–visible-doped ZnO@ZnCdS thin films exhibit reduced peak intensity upon Cu2⁺ addition. Also, optical absorption analysis shows a shift towards longer wavelengths in the emission of ZnO@ZnCdS due to Cu2⁺ inclusion during doping. Likewise, the band gap energy ranges from 1.37 eV to 2.22 eV for ZnO@ZnCdS and Cu2⁺ doped ZnO@ZnCdS, respectively, as determined using Tauc plots. PL spectrum of the Cu2⁺ doped ZnO@CdS nanocomposite indicates emissions in the blue and green regions. Specifically, under 325 nm excitation, the copper-doped material displays a prominent blue and a less intense red emission at 420 nm at 685 nm, respectively. Furthermore, the electrochemical analysis revealed that doping caused a reduction in Rct and an elevation in CSP. These results offer important considerations for the development of cutting-edge functional optoelectronic materials.

Vaporchromic Domino Transformation and Polarized Photonic Heterojunctions of Organoplatinum Microrods.

Photonic heterostructures with codable properties have shown great values as versatile information carriers at the micro and nanoscale. These heterostructures are typically prepared by a step-by-step growth or post-functionalization method to achieve varied emission colors among different building blocks. In order to realize high-throughput and multivariate information loading, we report here a strategy to integrate polarization signals into photonic heterojunctions. A U-shaped di-Pt(II) complex is assembled into highly-polarized yellow-phosphorescent crystalline microrods (Y-rod) by strong intermolecular Pt···Pt interaction. Upon end-initiated desorption of the incorporated CH2Cl2 solvents, Y-rod is transformed in a domino fashion into tri-block polarized photonic heterojunctions (PPHs) with alternate red-yellow-red emissions or red-phosphorescent microrods (R-rod). The red emissions of these structures are also highly polarized; however, their polarization directions are just orthogonal to those of the yellow phosphorescence of Y-rod. With the aid of a patterned mask, R-rod is further programmed into multi-block PPHs with precisely-controlled block sizes by side-allowed adsorption of CH2Cl2 vapor. X-ray diffraction analysis and theoretical calculations suggest that the solvent-regulated modulation of intramolecular and intermolecular excited states is critical for the construction of these PPHs.

Upconverting Ultra-Thin Bi2O2CO3 Nanosheets for Synergistic Photodynamic Therapy and Radiotherapy.

Synergistic therapy has become the major therapeutic method for malignant tumors in clinical. Photodynamic therapy (PDT) and radiotherapy (RT) always combine together because of their identical anti-tumor mechanisms, that is reactive oxygen species are generated by the use of radiosensitizers after irradiation by X-ray to efficiently kill cancer cells, PDT also follows similar mechanism. Full exposure of energy-absorbing species in nanomaterials to X-ray or near-infrared light irradiation makes the energy interchange between nanomaterials and surrounding H2O or dissolved oxygen easier, however, it remains challenging. Herein, an ultrathin two-dimensional (2D) nanosheet (NS) is developed, Bi2O2CO3, doped with lanthanide ions to give out upconversion luminescence, where the high Z elements Bi, Yb, and Er promote the radio-sensitizing effect. To the surprise, lanthanide activator ions gave out completely different luminescence properties compared with traditional upconversion nanoparticles. Less dopant of Er ions in nanosheets lattice resulted in brighter red emission, which provides more efficient PDT. Under RT/PDT combined treatment, NS shows a good tumor growth-inhibiting effect. In addition, synergistic therapy requires lower radiation dose than conventional radiotherapy and lower light power than single photodynamic therapy, thus greatly reducing radiation damage caused by RT and thermal damage caused by PDT.

Effect of Sm3+ concentration on reddish orange photoluminescence and electrochemical properties of copper aluminate nanoparticles for display and supercapacitor applications

In this report, a novel synthesis method for Sm3+-doped copper aluminate nanoparticles (1–9 mol %) is presented, utilizing Ocimumsanctum leaves extract as a reducing agent through the solution combustion method, followed by calcination at 600 °C for 3 h. The resulting cubic spinel structure, validated by Bragg reflections, demonstrates a decrease in crystallite size and a direct energy band gap correlated with increasing dopant concentration. The morphology exhibits irregularly shaped nanoparticles and hexagonal shaped nanoplates. On deconvolution, three peaks situated at 579, 590 and 600 nm. The emission peak observed at 579 and 590/600 nm can be attributed to transitions from excited level G5/24 to its lower lying levels, H5/26, H7/26 respectively, with noticeable concentration quenching at 7 mol %. CIE and CCT coordinates affirm the red emission of Sm3+ within the host lattice, suggesting potential applications in residential and hospital settings. Cyclic voltammetry analysis provides insights into redox reactions, electrode kinetics, and electrochemical behavior. Electrochemical Impedance Spectroscopy (EIS) elucidates ion transport kinetics, while Galvanostatic Charge–Discharge (GCD) analysis determines supercapacitance values ranging from 53.89 F/g with increasing dopant concentrations. This material exhibits promise for applications in energy storage and display technology.

Biomass-derived multiatom-doped carbon dots for water sensing based on excited state intraparticle proton transfer in organic solvents

The presence of trace water impurities in organic solvents can significantly influence chemical reactions and product quality; thus, the accurate detection of water content in these solvents is a critical requirement for industrial applications. Accordingly, an eco-friendly, effective, and economical sensor for detecting trace quantities of miscible water in organic solvents is required for industrial applications. In this study, we synthesized biomass-derived multi-atom-doped carbon dots (MACDs) as fluorescent probes and employed them for the detection of trace amounts of water impurities in several water-miscible organic solvents. The MACDs exhibited stable dual-color fluorescence emission under ultraviolet light irradiation and red and blue emissions in organic solvents and water. The fluorescence quantum yield was approximately 11 %, which indicates an excited intraparticle proton transfer response due to an increase in the water content within a wide response range from 0 % to 100 % (v/v) in organic solvents. The intensity of the red emission signal at 670 nm gradually decreased with an increase in the water content in the organic solvent. The MACDs could detect water with an instant response time of 55 s, a high sensitivity, and low limits of detection of 0.08 %, 1.36 %, 0.03 %, 0.04 %, 0.12 %, and 0.05 % (v/v) in ethanol, acetonitrile, dimethylformamide, methanol, isopropanol, and tetrahydrofuran, respectively. Hence, biomass-derived MACDs can serve as efficient and eco-friendly water sensors in organic solvents.

Effective red emission of Sb3+ sensitized Ho3+ doped Cs2NaGdCl6 perovskite under blue excitation

Red LEDs excited by blue light have a wide range of applications in plant growth due to their simple structure. The preparation of efficient red phosphors has attracted much attention from researchers. In this paper, Cs2NaGdCl6:Ho3+ Sb3+ phosphors were synthesized by the solvothermal method, which produced the characteristic emission of Ho3+5F5→5I8 at 655 nm under 460 nm excitation. The red light at 655 nm is further enhanced after the introduction of Sb3+, and the quantum efficiency can reach 39.85 %. The luminescence mechanism and energy transfer of Sb3+ and Ho3+ were further investigated. The produced phosphor was encapsulated with a 460 nm blue chip into an LED to realize red and blue dual emission, which meets the demand for blue and red light for plant growth.

Dual-emissive gold nanocluster / polylysine complex for ratio and visual luminescent detection

Heavy metals pollution shows a serious threat to global human and animal populations. Especially, mercury ions (Hg2+) are non-biodegradable and could accumulated through the food chain, causing severe damage to central nervous system and immune system. The sensitive and rapid detection of Hg2+ is important for human safety. In this study, based on the host–guest interaction between D-penicillamine (DPA) modified AuNCs and polylysine (PLL), a AuNCs@PLL complex system is constructed. The network of PLL enhances the luminescence properties of AuNCs through electrostatic interaction and hydrogen bonding. In combination with the blue emission of PLL, the AuNCs@PLL complex exhibits dual-emitting luminescence, which could be employed as a promising luminescent probe for Hg2+ detection. The high-affinity metallophilic Hg2+-Au+ interactions leads to the decomposition of AuNCs and consequently quenches the red emission, but the blue emission originating from PLL is unaffected. Based on this characteristic, a ratio luminescent probe targeted for quick accurate detection of Hg2+ is developed. Furthermore, paper test strips were fabricated employing the AuNCs@PLL luminescent probe for visual semi-quantitative Hg2+ detection. In addition to the benefits for sustainable development of the environment, health of the human, this study also has theoretical values for understanding the mechanism of NCs self-assembly.

Synthesis, structure and red-light emission of a manganese halide directed by a methyldiphenylphosphine oxide complex.

Controlling the optical activity of halide perovskite materials through modulation of the coordination configurations of the metal ions is important. Herein, a novel manganese-based halide, specifically diaquatetrakis(methyldiphenylphosphine oxide)manganese(II) tetrachloridomanganate(II), [Mn(C13H13OP)4(H2O)2][MnCl4] or [Mn(MDPPO)4(H2O)2][MnCl4] (MDPPO is methyldiphenylphosphine oxide), was synthesized through the solvothermal reaction of MnCl2 with the neutral molecule MDPPO. In this compound, [Mn(MDPPO)4(H2O)2]2+ acts as the cation, while [MnCl4]2- serves as the anion, enabling the co-existence of tetrahedral and octahedral structures within the same system. Remarkably, the compound exhibits efficient red-light emission at 662 nm, distinct from the green-light emission typically observed in MnX4-based halides. Theoretical calculations show that the red emission comes from the charge transfer from the MDPPO to the Mn2+ of [MnCl4]2-. This work provides a new perspective for the design and synthesis of red-light-emitting manganese-based halides with unique structures.

A zero-dimensional perovskite with high-efficiency luminescence and transient response for advanced information encryption

Due to the increasingly complex network attacks and advancements in computational technology, finding new and efficient encryption techniques is an urging task. As a promising material, the application of perovskite luminescent materials in information encryption is limited to pre-planned specific scenarios or applications, lacking the ability to respond to temporary demands. In this work, we have designed a novel cadmium-based zero-dimensional perovskite, TEA2CdCl4, which presents blue luminescence centered at 413 nm originating from organic cations. Upon Sb3+ doping, it not only exhibits intense red emission at 623 nm with a high photoluminescence quantum efficiency up to 100 %, but also brings outstanding resistance to thermal quenching. Especially, an ultrafast response speed could be achieved during decryption process which has been verified by first-principles calculations. Based on the advantages, a large-area optical anti-counterfeiting paper for temporary information encryption transmission is designed, which not only verifies the potential for secure information transmission and protection, but also introduces a new concept for the application of organic–inorganic hybrid perovskites in the field of information encryption.

Characterization of a thermally stable red-light-emitting phosphor: synthesis, photoluminescence, and thermoluminescence studies of CsCaF3 compound doped with Eu3+ for solid-state lighting applications

In this investigation, we focused on the synthesis and characterization of CsCaF3 compound doped with europium (Eu3+) ions using a solid-state route. To analyze the crystal structure of the synthesized phosphors, X-ray diffraction analysis was employed. Additionally, the doped sample underwent examination of surface morphology and elemental composition through Field Emission Scanning Electron Microscopy and EDAX mapping. The color of the pure and doped CsCaF3 sample was quantified and fitted using Color coordinate graph by the Commission Internationale de l'Eclairage (CIE). The red emission on the doped CsCaF3 compound was detected at 465 nm, which is the transition from 5D0 to 7Fj (j = 0, 1, 2, and 3). The 0.5 mol. % Eu3+ doped CsCaF3 sample was found to have a color purity of 81% and an associated color temperature of 1660 K, indicating its suitability for aesthetic lighting applications. Furthermore, thermoluminescence study, electron paramagnetic resonance (EPR), and effective atomic number (Z eff) calculations were conducted to provide valuable information for potential radiation dosimetry applications.

Excellent Electroluminescent Property of Eu3+-Induced Polystyrene-co-poly(acrylic acid) Aggregates (EIPAs) in Polymeric Light-Emitting Diodes.

Eu3+-induced polystyrene-co-poly(acrylic acid) aggregates (EIPAs) were synthesized using a self-assembly approach, and their structures and photophysical characteristics were examined to achieve effective monochromatic red emission in polymer light-emitting diodes (PLEDs). By adjusting the monomer ratio in RAFT polymerization, the size of Eu3+-induced block copolymer nanoaggregates can be regulated, thereby modulating the luminescence intensity. High-performance bilayer polymer light-emitting devices were fabricated using poly(9,9-dioctylfluorene) (PFO) and 2-(tert-butylphenyl)-5-biphenylyl-1,3,4-oxadiazole (PBD) as the host matrix, with EIPAs as the guest dopant. The devices exhibited narrow red emission at 615 nm with a full width at half-maximum (fwhm) of 15 nm across doping concentrations of 1, 3, 5, and 10 wt %. At a doping concentration of 3 wt %, the device achieved a maximum brightness of 1864.48 cd/m2 at 193.82 mA/cm2 and an external quantum efficiency of 3.20% at a current density of 3.5 mA/cm2. These results indicate that incorporating polystyrene-co-poly(acrylic acid) with Eu3+ complexes enhances the excitation and emission intensity, as well as the structural stability of the emitting layer in PLEDs, thereby improving the device performance.

First Principles Study of Europium doped Gallium Nitride in Wurzite Structure

In the present work, we have successfully deposited Sb antimony doped tin dioxide (SnO2) thin films with Several advantages over well known LCD's including increased brightness and viewing angle. We are currently investigating Eu doped GaN as a potential red phosphor for TEFL display applications. Eu doped GaN films were grown by solid source molecular beam epitaxy on Si (111) substates. The material was optically characterized through temperature dependent emission spectroscopy using a He-Cd laser at 325 nm for above band gap excitation. A strong red emission was obtained at 622 nm, which corresponds to an Eu3+ inner 4f-shell transition from the 5D 0 to 7F2 state. Therefore, the observed thermal quenching of red Eu emission is assigned to a strongly temperature dependent pumping process.

Dual-aeolotropic electrically conductive flexible composite membrane with enhanced red fluorescence

New-typed dual-aeolotropic conductive flexible composite membrane (DCFCM), was devised and fabricated by parallel electrospinning. DCFCM consists of two layers that are strongly coupled to form a top-to-bottom structure. Janus nanoribbon (JN), possessing two distinct sides (respectively conducting and insulating-fluorescent side), is highly oriented in each layer of DCFCM. The top-to-bottom structure of DCFCM effectuates the macro-level zoning, and the JN as a conductive and constitutive function in DCFCM realizes the micro-level zoning, which achieves the combination of microstructure and macroscopic structure in DCFCM. Thus, DCFCM simultaneously performs dual-aeolotropic electrical conduction and enhanced red luminescence due to the partitioning structures which aid in minimizing adverse interactions between the conductive and luminescent materials. The conducting anisotropy of each layer in the DCFCM can be adjusted by varying the PANI content. The conductance ratio can reach 108 when the PANI content is 60–70 %. Additionally, DCFCM exhibits strong red emission, originating from the allowed 5D0→7F2 (593 nm), 5D0→7F2 (616 nm) energy levels transitions of Eu3+ ions. This work provides a simple and effective method to fabricate aeolotropic conductive membranes with novel multifunctional properties.

Microstructural evolution and luminescence properties of multi-excitable cubic-ZrW2O8:Dy3+ nanorods for white light applications

ZrW2O8 nanorods doped with various concentrations of Dy3+ ions (5 - 15 mol%) showing excellent photoluminescence (PL) properties were synthesized by the facile hydrothermal method for white light applications. The products were comprehensively analyzed using a range of structural, morphological, and optical techniques. The optical studies were conducted by utilizing UV–visible and photoluminescence spectrophotometers. The photoluminescent emission spectra exhibit two prominent peaks at wavelengths of 479 nm and 572 nm, along with a less intense peak at 661 nm when subjected to excitations at wavelengths of 286 nm and 352 nm, and a highly dominating yellow emission with a faint red emission was obtained at 452 nm excitation. The almost constant value Y/B intensity ratios, lifetime values, CIE coordinates, and CCT values suggest that the obtained nanophosphor can be effectively employed in white light-emitting diodes (WLEDs) and various other lighting devices.

Sol–gel derived red fluorescent nanocomposites of copper nanoclusters conjugated silica for visualizing latent fingerprints

Phosphors with red emission have attracted increasing interests due to their high contrast and low interferences of fluorescence background which play a vital role in visualizing latent fingerprints (LFPs) in forensic science. In this work, red-emissive fluorescent nanocomposites of copper nanoclusters conjugated silica (CuNCs/silica) are prepared simply by sol-gel method in one pot for visualizing the LFPs through powder-dusting method. The CuNCs/silica exhibits the red fluorescence with an emission wavelength of 628 nm under the excitation of 292 nm and can have sufficient affinity with the LFPs ridges. The CuNCs/silica with the photoluminescence properties can precisely visualize and capture the clear patterns and the well-defined details of the LFPs ridges on the non-porous and semi-porous surfaces of different substrates (including copper foil, compact disc, tiles, stainless steel, aluminum foil, glass slide, Hong Kong currency, colored plastic packing, colored paper and leather) even with fluorescent background. The ridge details of the aged LFPs can also be clearly identified. These suggest the great potential of the CuNCs/silica as phosphors for visualizing the LFPs in criminal investigations.

Enhanced red emission of MgAl2O4: Cr3+/Mn4+ phosphor co-doped with alkali metal ions

A series of MgAl2O4: Cr, Mn, M (M = Li, Na, K) red phosphors were prepared by solution combustion combined with subsequently annealing treatment. The influence of Cr3+ or Mn4+ single-doping, Cr3+ and Mn4+ double-doping and alkali metal ions co-doping on the luminescence performance of MgAl2O4 phosphors were systematically investigated. XRD and SEM were used to characterize the composition and morphology of the phosphors, and the optical absorption, photoluminescent excitation, photoluminescent emission, fluorescence lifetime and chromaticity coordinate were performed to characterize their luminescence properties. Compared with Cr3+ or Mn4+ single-doped MgAl2O4 phosphors, Cr3+ and Mn4+ double-doped ones can achieve red light emission under a wide range of excitation from ultraviolet to visible light. Co doping with alkali metal ion Li enhances the fluorescence intensity and lifetime of MgAl2O4: Cr, Mn phosphors.