Orange Spectral Region Research Articles

Luminescent properties of Tm3+-activated phosphors with rosiaite structure

A series of solid solutions with compositions of La1-xTmxGa0.5Sb1.5O6 (x = 0.03, 0.05, 0.1) and La1-x-y-zTmxTbyDyzGa0.5Sb1.5O6 (x = 0.04, 0.07, 0.1; y = 0.04, 0.07, 0.1; z = 0.04, 0.04, 0.06) has been synthesized. It is shown that all the compounds have rosiaite structure (PbSb2O6, sp.gr. P-31m). Morphology, spectral-luminescent characteristics and color coordinates of the samples were studied. It was found that luminescence spectrum of thulium-activated samples recorded upon 351 nm excitation is typical for Tm3+ ions. At the same time, under excitation by radiation with λ = 457 nm and a power density of J = 4.7 kW/cm2, broadband thermal emission is observed, against which the bands corresponding to the 1G4→3H6, 1G4→3F4, 3F4→3H6 и 3H4→3H6 transitions of Tm3+ are detected. The luminescence spectra of the samples co-activated with Tm3+, Tb3+ and Dy3+are characterized by a relatively low intensity of the Tm3+ emission, which may be due to efficient energy transfer processes between Tb3+ and Dy3+ ions. A shift from the blue to the green color regions is observed in the color coordinates of the co-activated samples upon 351 nm excitation. Radiation with λ = 457 nm led to a shift in the emission colour to orange. Thus, it is shown that it is possible to create phosphors emitting in the blue, green and orange spectral regions by changing the wavelength of exciting radiation and activator composition for compounds with rosiaite structure.

Orange/red light emitting iridium(III) organometallic complexes containing 2,3‐di(pyridine‐2‐yl)quinoxaline as ancillary ligand and their anticancer properties

AbstractA π‐electron rich ligand, 2,3‐di(pyridine‐2‐yl)quinoxaline, was introduced in Ir(III) coordination sphere along with four different cyclometallating ligands to obtain four new complexes (Ir1–Ir4) of formula [Ir(C N)2(pyrquinox)]PF6 {where C N is monoanionic cyclometallating ligand; 2‐phenylpyridine (ppy), 2‐(2,4‐difluorophenyl)‐5‐(trifluoromethyl)pyridine (F2CF3ppy), 2,5‐diphenylbenzoxazole (phox), 2,3‐diphenylquinoxaline (phquinox) and pyrquinox=2,3‐di(pyridine‐2‐yl)quinoxaline}. Structure of Ir1 was determined from single crystal X‐ray structure analysis and found it to be a bis‐heteroleptic Ir(III) mononuclear octahedral complex of formula [Ir(ppy)2(pyrquinox)]PF6. A very same structural formulation of Ir2–Ir4 was supported by different spectroscopic and analytical data. Theoretical calculations were helpful in understanding the optical and electrochemical properties of Ir1–Ir4. The effect of rich π‐electrons ancillary ligand (pyrquinox) was observed on luminescence properties of the complexes, which on irradiation produced emissions in the orange and red spectral regions. The cytotoxic behaviours of Ir1–Ir4 were explored against MCF‐7 cell line through MTT assays. The obtained IC50 values were found in low micromolar region (5–8 μM) and displayed comparatively higher cytotoxicity behaviour to cis‐platin.

Norbornene-Substituted Cationic Iridium(III) Complex and Water-Soluble Luminescent Polymers Based on It: Synthesis, Photophysical and Cytotoxic Properties

A norbornene-substituted cationic iridium(III) complex containing 1-phenylisoquinoline cyclometalating ligands and an additional phenylimidazophenanthroline ligand was synthesized. On the base of this complex, water-soluble polymers were obtained by ring-opening metathesis polymerization (ROMP). The resulting polymers showed oxygen-dependent phosphorescence in the orange spectral region and high cytotoxicity against HCT116 cancer cells.

Investigation of spectroscopic properties of Sm3+ doped phosphate glasses for reddish orange light applications

Samples of phosphate glasses with composition of (40-x) P2O5-40Na2O-20ZnO-xSm2O3, with Sm3+ ion concentration varying from 0.1 to 2.5%, were synthesized using melt quenching technique and characterized by X-Rays Diffraction, UV–Vis and luminescence spectroscopies. Using Judd-Ofelt analysis, the parameters Ω2, Ω4 and Ω6 of Sm3+ (4f7) were determined. Three transitions of Sm3+: 4G5/2→ 6H5/2, 6H7/2, 6H9/2 were observed from the luminescence spectra. The radiative (τr) and the measured (τmea) lifetimes for 4G5/2 level, were discussed and compared with other works. The quantum efficiency (η) is found to be higher for × = 0.5 mol % of Sm2O3. The CIE chromaticity coordinates were calculated, and it was found that PSm glasses can be suitable for the development of visible lasers in the orange red spectral region.

Tuning the Photometric Properties of Ternary Sm3+ Complexes Involving Mixed-Ligands.

This research article deals with the synthesis of ternary Sm3+ complexes with 6,8-dichlorochromone-3-carboxaldehyde through solution-precipitation method. The photometric properties of resultant complexes were tuned by coordinating N-donor heterocyclic ligands with Sm3+ ion. The emission spectra, obtained in the visible region have been studied. Under optical excitation of 370nm, the complexes displayed characteristic Sm3+-centered emission peaks at ~ 563, 600 and 647nm in solution as well as in powder state. The complexes showed thermal stability up to 175°C. The complexes delivered quantum yield as high as 7.91% and longest emission lifetime of 0.564ms. The color coordinates of the complexes, located in deep orange (in solution) and red (in powder) spectral region, matched well with the Society of Motion Picture and Television Engineers and European Broadcasting Union. The properties of complexes have been investigated to a significant extent due to their easy synthesis and potential applications as orange-red light emitter in a wide range of photonic applications such as display devices, OLEDs, dashboards, optical systems.

A Novel Electrically Conductive Perylene Diimide‐Based MOF‐74 Series Featuring Luminescence and Redox Activity

Metal‐organic frameworks (MOFs) featuring significant electrical conductivity constitute a growing class of materials, with intriguing possible applications as porous semiconductors or supercapacitors. If such features are combined with photoluminescence (PL), additional functionalities such as selective chemical sensing become accessible. Here, perylene diimide (PDI)‐based linear building blocks are incorporated into the MOF‐74 topology with the three metal ions Zn2+, Mg2+, and Ni2+, resulting in a new series of MOFs, namely PDI‐MOF‐74(M). PDI derivatives are dye molecules exhibiting remarkable optical properties, high electron mobilities, as well as interesting redox behavior. However, PDI‐based 3D MOFs are very rare and to date were only reported once. The frameworks of the PDI‐MOF‐74(M) series exhibit high crystallinity, electrical conductivity, and show well‐defined redox activity. In addition, the frameworks of the series feature PL in the orange and red spectral regions. Herein, the series of electroactive MOF‐74 structures as well as the group of 3D PDI‐based MOFs is expanded, hence opening up the development of novel MOFs with promising optoelectronic properties comprising PDI building blocks.

A novel Eu3+-doped ScCaO(BO3) red phosphor for tricolor-composited high color rendering white light

Exploration of novel red emitting phosphors containing Eu3+ ions is an everlasting topic in the field of luminescent materials due to the application requirement of warm white light-emitting diodes. In this work, the Eu3+-doped ScCaO(BO3) phosphors were synthesized though the high temperature solid-state reaction method. The phase purity and detail information on crystal structure were obtained by X-ray diffraction (XRD) and the technology of Rietveld XRD refinement. Scanning electron microscopy (SEM) was applied to check the particle morphology and EDS mapping was taken to analyze element distributions. Optical properties of the phosphors were studied by measuring the steady-state excitation and emission spectra and also the transient luminescence decays. The emission spectra of ScCaO(BO3):Eu3+ majorly consisted of 5D0-7F1, 7F2 and 7F4 transitions, covering the orange (582–605 nm), red (605–635 nm) and deep red (690–720 nm) spectral regions. The doping concentration of Eu3+ ions was optimized to 12% to maximize the optical performance of the red emitting phosphors, whose CIE coordinate and fluorescent lifetime were (0.6458, 0.3537) and 1.516 ms, respectively. The investigation of the thermal quenching behavior of the ScCaO(BO3):0.12Eu3+ phosphor reveals that the emission intensity of Eu3+ at 400 K can maintain 68.98% of that at room temperature due to the existence of the thermal activation energy of 0.258 eV. Using such a red-emitting material, the prototype warm white LED device with the CIE coordinate of (0.3262, 0.3363), color rendering index of 86.1 and correlated color temperature of 5871 K can be obtained by combining with the blue emitting BaMgAl10O17:Eu2+ and green emitting Zn2SiO4:Mn2+ phosphors and coating all three on a near-UV LED chip. All the results demonstrate that the ScCaO(BO3):0.12Eu3+ phosphor can sever as a potential red emitting candidate for near-UV excited warm WLEDs.

Solution-Processed OLEDs Based on Thermally Activated Delayed Fluorescence Copper(I) Complexes with Intraligand Charge-Transfer Excited State.

A new series of tetrahedral heteroleptic copper(I) complexes exhibiting efficient thermally-activated delayed fluorescence (TADF) in green to orange electromagnetic spectral regions has been developed by using D-A type N^N ligand and P^P ligands. Their structures, electrochemical, photophysical, and electroluminescence properties have been characterized. The complexes exhibit high photoluminescence quantum yields (PLQYs) of up to 0.71 at room temperature in doped film and the lifetimes are in a wide range of 4.3–24.1 μs. Density functional theory (DFT) calculations on the complexes reveal the lowest-lying intraligand charge-transfer excited states that are localized on the N^N ligands. Solution-processed organic light emitting diodes (OLEDs) based on one of the new emitters show a maximum external quantum efficiency (EQE) of 7.96%.

Multicolor emission and energy transfer dynamics in thermally stable Dy3+/Eu3+ co-doped ZPBT glasses for epoxy free w-LEDs application

Dy3+ doped and Dy3+/Eu3+ co-doped zinc phosphate barium titanate (ZPBT) glasses were successfully synthesized by melt quenching procedure. The co-doped glasses revealed emission peaks in the blue, yellow, orange, and red spectral regions. The combinations of these emission yield white light (cool, neutral, and warm) and orangish-red light. The tunable emission is attained by appropriately regulating Eu3+ concentrations and excitation wavelengths. The emission and decay analysis revealed the energy transfer arising due to dipolar-dipolar interaction from Dy3+ to Eu3+. The emission intensity and the chromaticity shift observed at 423 K were 72.54 % and 7.74 ×10−3, respectively signifying the strong thermal stability of the co-doped ZPBT glass. An epoxy-resin free device was demonstrated using 1.0 mol% Dy3+/Eu3+ co-doped glass and 385 nm n-UV LED chip. The results mentioned-above indicate that Dy3+/Eu3+ co-doped synthesized glasses are promising candidates for epoxy-free high powered w-LED applications under n-UV excitation.

Blue diode-pumped single-longitudinal-mode Pr:YLF lasers in orange spectral region

We report on blue diode-pumped single-frequency Pr:YLF lasers in orange spectral region, for the first time to the best of our knowledge. For a single-frequency σ-polarized 607 nm laser, a maximum output power up to 175 mW is achieved with a slope efficiency of about 16.6%. Linewidth of the 607 nm single-frequency laser is measured to be about 6 MHz. Single-frequency operation has also been obtained at π-polarized 604 nm laser with a maximum output power up to 91 mW and a slope efficiency of about 8.9%. The corresponding linewidth of the 604 nm laser is about 22 MHz. The two single-frequency orange lasers exhibit wavelength tuning ranges of about 0.15 nm and 0.35 nm, respectively. This work has proposed the simplest way for single-frequency laser generation in orange spectral region, which could be obtained by complicated and low-efficiency sum-frequency mixing of Nd3+ lasers. This work paves a practical way for various orange-related applications.

Facile Preparation of Stable Solid-State Carbon Quantum Dots with Multi-Peak Emission.

Aggregation-caused quenching (ACQ) effect, known as the main cause to restrain solid-state luminescence of carbon quantum dots (CQDs), hinders further application of CQDs in white light-emitting diodes (WLED). Here, a complex of CQDs and phthalimide crystals (CQDs/PC) was prepared through a one-step solvothermal method. CQDs/PC prevented CQDs from touching directly by embedding the CQDs in phthalimide crystal matrix in situ, which effectively reduced the ACQ effect. Furthermore, CQDs/PC exhibited multi-peak fluorescence spectra that span the green, yellow and orange spectral regions. Finally, a WLED fabricated based on CQDs/PC achieved a color-rendering index of 82 and a correlated color temperature of 5430 K. This work provides a quick and effective strategy to apply CQDs to WLED.

Electromagnetic analysis of the lasing thresholds of hybrid plasmon modes of a silver tube nanolaser with active core and active shell.

Results from the electromagnetic modeling of the threshold conditions of hybrid plasmon modes of a laser based on a silver nanotube with an active core and covered with an active shell are presented. We study the modes of such a nanolaser that have their emission wavelengths in the visible-light range. Our analysis uses the mathematically grounded approach called the lasing eigenvalue problem (LEP) for the set of the Maxwell equations and the boundary and radiation conditions. As we study the modes exactly at the threshold, there is no need to invoke nonlinear and quantum models of lasing. Instead, we consider a laser as an open plasmonic resonator equipped with an active region. This allows us to assume that at threshold the natural-mode frequency is real-valued, according to the situation where the losses, in the metal and for the radiation, are exactly balanced with the gain in the active region. Then the emission wavelength and the associated threshold gain can be viewed as parts of two-component eigenvalues, each corresponding to a certain mode. In the configuration considered, potentially there are three types of modes that can lase: the hybrid localized surface plasmon (HLSP) modes of the metal tube, the core modes, and the shell modes. The latter two types can be kept off the visible range in thin enough configurations. Keeping this in mind, we focus on the HLSP modes and study how their threshold gain values change with variations in the geometrical parameters of the nanotube, the core, and the shell. It is found that essentially a single-mode laser can be designed on the difference-type HLSP mode of the azimuth order m = 1, shining in the orange or red spectral region. Furthermore, the threshold values of gain for similar HLSP modes of order m = 2 and 3 can be several times lower, with emission in the violet or blue parts of the spectrum.

The dose-dependent photobleaching of CdTe quantum dots in aqueous media

The photobleaching of capped CdTe quantum dots (QDs) possessing a photoluminescence (PL) emission band in green or orange spectral regions (550 nm or 570 nm, respectively) was investigated in aqueous solution under irradiation with violet light. The exposure of QDs had a dose-dependent effect on the photoluminescence intensity revealing three main stages in the variable pattern of its decline. The relatively rapid decrease of PL intensity being observed after the initial doses of exposure was followed by its partial recovery in the dark. The decrease was slower during the middle stage, but become faster again under exposure to the highest cumulative doses. The stages detected in the photoluminescence decrease pattern were also distinguished by monitoring the capacity to recover the reduced PL intensity of QDs and observing the changes in PL spectra as well as absorption spectra. The gradual pattern of the photoluminescence changes is assumed to be a reflection of the photoinduced modification and disintegration of a capping layer of QDs.

Phase separation strategy to facilely form fluorescent [Ag2]2+/[Agm]n+ quantum clusters in boro-alumino-silicate multiphase glasses.

By adjusting the content of ZnF2-SrF2/ZnO-SrO, a series of SiO2-Al2O3-B2O3-Na2O-ZnO/ZnF2-SrO/SrF2-Ag multiphase glasses was designed and prepared via a melt-quenching method. Under a phase separation strategy, negatively charged tetrahedrons ([BO4]-, [ZnO4]2-, and [AlO4]-) can be generated to stabilize different silver species (Ag+ ions; [Ag2]2+ pairs; [Agm]n+ quantum clusters ([Agm]n+ QCs)) in B2O3-rich and ZnO-Al2O3 rich sub-phases. The B2O3-rich sub-phase has a high solubility for Ag+ ions and [Agm]n+ QCs. The fluoride-rich phase shows a good ability to extract Na+ from the B2O3-rich sub-phase, significantly affects the solubility of Ag+ in the B2O3-rich sub-phase, and eventually determines the aggregation from Ag+ ions and Ag0 atom to [Agm]n+ QCs. The ZnO-Al2O3-rich or ZnO-SiO2-rich (i.e. SiO2-rich in GZnOSrO) phase has a relatively high solubility for [Ag2]2+ pairs. The Ag+/[Ag2]2+/[Agm]n+ QC fluorescent centers were identified by spectroscopic analysis, where the fluorescence bands are located in the ultraviolet, green-white and orange spectral regions, respectively. The fluorescent quantum yield (QY) of the [Agm]n+ QCs can be improved to 55.7%, and the combination of these three luminescent centers can achieve white light emission.

Simultaneous detection of folic acid and methotrexate by an optical sensor based on molecularly imprinted polymers on dual-color CdTe quantum dots

In this work, molecularly imprinted polymers (MIPs) were used on the surface of cadmium telluride quantum dots (CdTe QDs) for the simultaneous determination of folic acid (FA) and methotrexate (MTX). For this purpose, two different sizes of CdTe QDs with emission peaks in the yellow (QDY) and orange (QDO) spectral regions were initially synthesized and capped with MIPs. FA and MTX were used as templates for the synthesis of the two composites and designated as QDY-MIPs and QDO-MIPs, respectively. Fourier transform infrared spectroscopy, transmission electron microscopy, and fluorescence spectroscopy were employed to characterize the composites. QDY-MIPs and QDO-MIPs were then mixed (to form QDs-MIPs) and excited at identical excitation wavelengths; they emitted two different emission wavelengths without any spectral overlap. The fluorescence signals of QDY-MIPs and QDO-MIPs diminished in intensity with increasing concentration of the corresponding template molecules. Under optimal conditions, the dynamic range was 0.5–20 μmol L−1 for FA and MTX, and the detection limits for FA and MTX were 32.0 nmol L−1 and 34.0 nmol L−1, respectively. The reproducibility of the method was checked for 12.5 μmol L−1 of FA and MTX to find RSD values of 4.2% and 6.3%, respectively. Finally, the applicability of the method was checked using human blood plasma samples. Results indicated the successful application of the method as a fluorescent probe for the rapid and simultaneous detection of FA and MTX in real samples.

New efficient laser dyes for the red spectral range. Part 2. Pyrone derivatives

We report the generation characteristics of ethanol solutions of some dyes belonging to the derivatives of 2H- and 4H- pyrones, as well as of some structurally similar model fluorophores. The tuning curves of these dyes generating light in the orange and red spectral regions are measured, and the wavelength tuning ranges are determined. The dependences of the generated energy on the pump energy in a non-selective cavity are also measured. It is shown that some of the studied compounds possess better characteristics than those of widely used laser dyes in these spectral regions.

New efficient laser dyes for the red region of the spectrum. Part 1. Peri-indenones

We report the generation characteristics of ethanol solutions of twenty newly synthesised dyes belonging to peri-indenones, including benzanthrones and phenalemines. The tuning curves of these dyes, generating light in the orange and red spectral regions, are measured, and the wavelength tuning ranges are determined. The dependence of the generation energy on the pump energy in a non-selective cavity is measured. It is shown that some of the synthesised dyes surpass the widely used laser dyes in the energy efficiency and the width of the wavelength tuning range.

Temperature dependent luminescence Cr3+-doped GdAl3(BO3)4 and YAl3(BO3)4

Chromium activated YAl3(BO3)4 (YAB) and GdAl3(BO3)4 (GAB) were synthesized and show efficient broad band near infrared emission under excitation in the UV, blue and orange spectral regions. Temperature dependent luminescence measurements for GAB:1%Cr3+ and YAB:1%Cr3+ reveal high quenching temperatures for the broad band Cr3+ emission, 620K for YAB:Cr and 650K for GAB:Cr. To gain insight in the luminescence the crystal field strength, Racah parameters, nephelauxetic effect and phonon coupling parameters have been investigated by using spectroscopic data. The crystal field splitting for Cr3+ is similar in the two borates (around 1670cm−1). However, the calculated B Racah parameters indicate a higher global covalency in GAB. The electron phonon-coupling parameter (S) and the effective phonon energy (ħω) were determined to be 5.9 and 263cm−1 for YAB and 5.4 and 309cm−1 for GAB, respectively. The larger electron–phonon coupling strength in YAB:Cr is in agreement with the lower quenching temperature in comparison with GAB:Cr.

Growth and diode-pumped laser operation of Pr3+:β-(Y0.5,Gd0.5)F3 at various transitions.

We report on the crystal growth of the orthorhombic low-temperature β-phase of (Y0.5,Gd0.5)F3 (YGF) single crystals. The crystals were activated with trivalent praseodymium (Pr3+) and characterized with respect to their ground state absorption and stimulated emission properties. Under InGaN-laser-diode pumping, laser oscillation was obtained at more than ten wavelengths in the green, orange, red, and dark red spectral regions. In these initial experiments, output powers exceeding 100 mW and slope efficiencies between 10% and 30% were obtained. To the best of our knowledge, these results represent the first application of YGF crystals as laser host material for any active ion.

Observation of the Ge-vacancy color center in microcrystalline diamond films

In germanium-doped thin polycrystalline diamond films grown in microwave plasma on Ge substrates, strong photoluminescence in the orange spectral region with a zero-phonon line (ZPL) at a wavelength of 602 nm is detected. The ZPL width is 4–5 nm at room temperature and 1.2 nm at T = 5K. It is assumed that the new optically active defect is a germanium–vacancy (Ge–V) complex similar to the known Si–V color center in diamond.