Blue-green Emission Research Articles

Growth and characterization of screen printed TiO2–CuO thick films for optoelectronic applications

We herein report, the deposition of pure and CuO doped TiO2 thick films on glass slides by a cost effective screen printing process, which were then sintered to obtain desired stochiometric composition. Different analytical approaches were used to reveal the precise structural, morphological, optical and electrical characteristics information of pure TiO2 and TiO2–CuO thick films. X-ray diffraction (XRD) patterns exhibit the formation anatase phase of TiO2 and monoclinic phase of CuO. Raman spectra show four TiO2 anatase phase modes only in 100–800 cm−1 region. Infrared (IR) transmittance spectra of these samples recorded in 4000–400 cm−1 region also showed weak, very weak and medium intensity stretching and bending modes of O–Ti–O and Ti–O–Ti bond groups of TiO2 only in 700–400 cm−1 region which further supported the formation of TiO2 anatase phase only. Scanning electron microscopy (SEM) images indicate porous surfaces morphology, irregular shaped as well as size polygonal and spherical shaped particles with tendency to form aggregates along with the EDS analysis that confirms proper composition of the films. The optical band gap energies were derived from diffused reflectance spectroscopy and photoluminescence (PL) spectra. They showed a red shift in peak positions which caused reduction in band gap energy. The CIE diagram clearly depicted blue-green and white emissions. I–V characteristics has been used for calculation of the diode parameters such as ideality factor (n) and barrier height (Φb). The extracted results such as band gap, particle size and electrical parameters suggest that the TiO2–CuO thick films can be used in photovoltaic applications.

Excellent photoluminescence and electrochemical properties of Sm3+ doped Ca2MgSi2O7 nanophosphor: Display and electrochemical sensor applications

A series of orange-red light emitting Ca2MgSi2O7:Sm3+ nanopowders were fabricated via low-cost eco-friendly green combustion technique using Aloe vera gel as fuel. The phase purity of the samples were confirmed by the powder X-ray diffraction (PXRD) technique. Pure single-phase tetragonal structure is observed from the PXRD results with no additional impurity peaks. The band gap energy of the fabricated powders was estimated by diffuse reflectance spectra (DRS) and is found to be in the range of 4.01–5.98 eV. A high resolution scanning electron microscope (SEM) was used to study the morphological behaviour of the samples. Honeycomb-like structures are observed from the SEM results. The particle size was evaluated by transmission electron microscopy (TEM) and is found to be ∼50 nm. The interplanar distance is found to be 0.53 nm. Photoluminescence properties were systematically studied in detail. The phosphors are successfully excited at 403 nm NUV light, producing reddish-orange characteristic emission. The emission peaks are centered at 558 (4G5/2 → 6H5/2), 607 (4G5/2 → 6H7/2) and 645 nm (4G5/2 → 6H9/2), respectively. Among the observed peaks the red emanation (4G5/2 → 6H7/2) is stronger than the orange emission (4G5/2 → 6H5/2) in the current investigation. The photoluminescent concentration quenching is noticed above 5 mol% Sm3+ ion doping content. The dipole–dipole interaction resulting in cross relaxation is found to be the principal cause of concentration quenching mechanism. The color features such as Commission Internationale de l’Eclairage (CIE) and correlated color temperature (CCT) were studied in detail. The optimized chromaticity coordinates were estimated to be (0.6363, 0.3632), which fall in the reddish-orange region. The average CCT value obtained is 3362 K. The average color purity is found to be ∼82%. Sm3+ incorporated Ca2MgSi2O7 samples are possible contender for single white light generation commercial candidates owing to their strong hypersensitivity of Sm3+ ions through host, least possibility for re-absorption of blue-green emission owing to poor direct f–f excitation of Sm3+ ions, and high color purity (reddish-orange emission). The prepared powders exhibit excellent electrochemical redox properties and CPE modified optimized powders show outstanding sensitive response which indicates its use in the potential electrochemical sensor materials for drug sensing studies.

Physical Characteristics, Blue-Green Band Emission and Photocatalytic Activity of Au-Decorated ZnO Quantum Dots-Based Thick Films Prepared Using the Doctor Blade Technique.

Nanoscale ZnO is a vital semiconductor material whose versatility can be enhanced by sensitizing it with metals, especially noble metals, such as gold (Au). ZnO quantum dots were prepared via a simple co-precipitation technique using 2-methoxy ethanol as the solvent and KOH as the pH regulator for hydrolysis. The synthesized ZnO quantum dots were deposited onto glass slides using a simple doctor blade technique. Subsequently, the films were decorated with gold nanoparticles of different sizes using a drop-casting method. The resultant films were characterized via various strategies to obtain structural, optical, morphological, and particle size information. The X-ray diffraction (XRD) reveals the formation of the hexagonal crystal structure of ZnO. Upon Au nanoparticles loading, peaks due to gold are also observed. The optical properties study shows a slight change in the band gap due to Au loading. Nanoscale sizes of particles have been confirmed through electron microscope studies. P.L. studies display blue and blue-green band emissions. The significant degradation efficiency of 90.2% methylene blue (M.B.) was attained in natural pH in 120 min using pure ZnO catalyst while one drop gold-loaded catalysts, ZnO: Au 5 nm, ZnO: Au 7 nm, ZnO: Au 10 nm and ZnO: Au 15 nm, delivered M.B. degradation efficiency of 74.5% (in 245 min), 63.8% (240 min), 49.6% (240 min) and 34.0% (170 min) in natural pH, respectively. Such films can be helpful in conventional catalysis, photocatalysis, gas sensing, biosensing, and photoactive applications.

Spectral and DFT/TD-DFT studies on turn-on fluorescent detection of Al(III) by a quinolin-8-ol-based Schiff base and its bioimaging

A new Schiff base (AK2) is synthesized, characterized and used to detect Al(III) ions as the fluorometric probe in an aqueous solution. AK2 exhibits high selectivity towards Al(III) by forming a 1:1 octahedral complex wherein the probe acts as a NNN-tridentate ligand. The sensing mechanism is verified by 1H NMR, 27Al NMR and mass spectral techniques in addition to Job's plot analysis. In an aqueous solution, AK2 is scarcely emissive due to the photoinduced electron transfer (PET) process and upon the addition of Al(III) ions the formed AK2+Al(III) complex results in instantaneous intense bluish-green emission (at 475 nm) by chelation-enhanced fluorescence (CHEF) effect. AK2 was found to have high selectivity, high binding constant (Kb = 3.9 × 104 M−1) and an acceptable limit of detection (LOD = 0.9 µM). The experimentally observed optical properties of AK2 and AK2+Al(III) complex have been correlated with computational results using B3LYP/6–311G** and B3LYP/LACV3P** basis sets by Density Functional Theory (DFT) and Time-dependent Density Functional Theory (TD-DFT) methods. The probe has proved its real-time application as a reagent in the quantitative determination of Al(III) in natural matrices such as bore water, drinking water, tap water and BSA solution. Fluorescence microscopic studies showed that AK2 could be used as an effective probe for detecting intracellular Al(III) in HeLa cells without toxicity.

Difluoroboron complexes of aromatic imidazole-functionalized 2-(benzo[d]thiazol-2-yl)phenol (BTZ): Synthesis and luminescence properties

Two aromatic imidazole-functionalized ligands (BTZ-PI-OH and BTZ-IM-OH) and their difluoroboron complexes (BTZ-PI-BF2 and BTZ-IM-BF2) were successfully synthesized by linking the aromatic imidazole units into 2-(benzo[d]thiazol-2-yl)phenol (BTZ-OH) via Suzuki-Miyaura cross-coupling reaction, and characterized by NMR (1H and 13C), HR-MS and FT-IR spectra. The photophysical, electrochemical properties and thermal stability of the ligands and the difluoroboron complexes were systematically investigated by experimental and theoretical methods to reveal their relationship between the molecular structures and photoelectric properties. The ligands exhibited dual fluorescence (enol emission and keto emission) due to the characteristics of excited-state intramolecular proton-transfer (ESIPT) in solution, while they showed only one emission in solid thin films. Compared with the ligands, the difluoroboron complexes showed a significant blue-shifted and enhanced emission due to the restricted conformation change. The solution-processed doped devices using the difluoroboron complexes as the emitting materials exhibited green-blue emission with maximum external quantum efficiency (EQEmax) of 1.35% for BTZ-PI-BF2 and 3.08% for BTZ-IM-BF2, respectively.

Enhanced Optical Nonlinearity in Bi3+-Doped CePO4 Nanostructures for Optical Limiting Applications

Pure and Bi3+-doped CePO4 were synthesized by the simple co-precipitation method. Successful dopant incorporation into the host lattice of orthophosphate without altering the crystalline structure was confirmed by structure analysis, X-ray diffraction, and Raman characterization. Morphological investigation was done using HR-SEM which portrays the co-existence of nanospheres and nanorods in doped CePO4 and only nanospheres in pure CePO4. X-ray photoelectron spectroscopy studies confirm the +3 oxidation state of Ce3+ and Bi3+ with the presence of a trace amount of Ce4+ in the as-prepared nanoparticles. Vibration sample magnetometer studies show weak ferromagnetic behavior of the nanostructures at room temperature. The absorption band in the wavelength range 200–300 nm accounts for 4f–5d electronic transition, and a red shift in the band edge is due to the increase in the band gap with the addition of the dopant. Photoluminescence emission spectra show broad blue-green emission owing to transition of Ce3+ from the excited state to the ground state and also due to oxygen vacancy. The nonlinear optical absorption and optical limiting (OL) behaviors of Bi3+-doped cerium orthophosphate (CePO4) were investigated using an open-aperture (OA) Z-scan technique under an excitation source of 532 nm nanopulsed lasers. The recorded OA transmittance curve reveals a transition from saturable absorption to reverse saturable absorption in pure CePO4 at 2.46 GW/m2, whereas all the doped samples exhibit RSA attributed to 2PA. The increase in the nonlinear absorption (NLA) coefficient with on-axis intensity and the availability of the near resonant energy state due to the Bi3+ dopant ensure the sequential 2PA (1PA + ESA) phenomenon. Compared to pure CePO4, doped nanostructures show improved NLA coefficients due to the availability of the defect state and oxygen vacancies in Bi3+-doped CePO4. Interestingly, a lower OL threshold (OLT) of 0.14 × 10–13 W/m2 is observed in 0.3% Bi3+-doped CePO4. The lower OLT value of Bi3+-doped CePO4 ensures its potential candidature for OL applications in protecting optical sensors and human eyes.

Highly Efficient Solution-Processed Bluish-Green Thermally Activated Delayed Fluorescence Compounds Using Di(pyridin-3-yl)methanone as Acceptor

Solution-processed devices with thermally activated delayed fluorescence (TADF) compounds have gained great attention due to their low cost and high performance. Here, two solution-processable TADF emitters named ACCz-DPyM and POxCz-DPyM were synthesized by coupled 9,10-dihydro-9,9-dimethylacridine or phenoxazine modified carbazole as donor with di(pyridin-3-yl)methanone as acceptor. Both TADF compounds show same small ΔΕST of 0.04 eV and high PLQY of 66.2% and 58.2%. The devices fabricated by ACCz-DPyM and POxCz-DPyM as emitters show excellent performance as solution-processed with low turn-on voltage of 4.0 and 3.4 V, high luminance of 6209 and 3248 cd m−2 at 8 V, the maximum current efficiency of 9.9 and 15.9 cd A−1, the maximum external quantum efficiency of 6.6% and 6.5% and low efficiency roll-off. The solution-processed device based on ACCz-DPyM shows bluish-green emission. These results show that ACCz-DPyM and POxCz-DPyM are suitable for solution processing devices.

Dual-emitting cellulose nanocrystal hybrid materials with circularly polarized luminescence for anti-counterfeiting labels

Cellulose nanocrystal (CNC) hybrid materials with numerous optical states have great potential as anti-counterfeiting labels and information encryption materials. However, it is challenging to construct multicolor emitting materials with tunable behaviors, which can dramatically enhance anti-counterfeiting abilities. Here, free-standing composite films with vivid multi-structural colors and dual-emitting fluorescence are successfully fabricated through a host-guest coassembly strategy. The lanthanide complex and an aggregation-induced emission molecule (tetraphenylethylene derivative, TPEC) are selected as luminescent guests, which are integrated into the chiral nematic structure of CNCs. The obtained photonic films display broadband reflection across the visible spectrum, which may be attributed to the chiral nematic domains with variations in the helical pitches and helical axis orientations. Under 254 nm excitation, the film exhibits bright red emission, while blue–green emission switching occurs under 365 nm excitation. The broad reflection band of the film covers both the green and red fluorescent emission centers, and right circularly polarized luminescence emission with different dissymmetry factors is produced due to the selective reflection of the left chiral nematic structure. A large glum value up to −0.21 at 600 nm was realized. Additionally, CNC-based materials with tailored shapes are further used in anti-counterfeit tags and decorative applications.

Synthesis of Visible Light Excitable Carbon Dot Phosphor-Al2 O3 Hybrids for Anti-Counterfeiting and Information Encryption.

The preparation of room temperature phosphorescent carbon dots still faces great challenges, especially in the case of carbon dots endowed of visible-light excitable room temperature phosphorescence (RTP). To date, a limited number of substrates have been exploited to synthesize room temperature phosphorescent carbon dots, and most of them can emit RTP only in solid state. Here, the synthesis of a composite obtained from the calcination of green carbon dots (g-CDs) blended with aluminum hydroxide (Al(OH)3 ) is reported. The resultant hybrid material g-CDs@Al2 O3 exhibits blue fluorescence and green RTP emissions in an on/off switch process at 365nm. Notably, this composite manifests strong resistance to extreme acid and basic conditions up to 30 days of treatment. The dense structure of Al2 O3 formed by calcination contributes to the phosphorescent emission of g-CDs. Surprisingly, g-CDs@Al2 O3 can also emit yellow RTP under irradiation with white light. The multicolor emissions can be employed for anti-counterfeiting and information encryption. This work provides a straightforward approach to produce room temperature phosphorescent carbon dots for a wide range of applications.

The Influence of Ablation Speed on the Synthesis of Carbon Nanostructures Via Pulsed Laser Ablation of Asphalt in Ethanol

Pulsed liquid laser ablation is considered a green method for the synthesis of nanostructures because there are no byproducts formed after the ablation. In this paper, a fiber laser of wavelength 1.064 µm, peak power of 1 mJ, pulse duration of 120 ns, and repetition rate of 20 kHz, was used to produce carbon nanostructures including carbon nanospheres and carbon nanorods from the ablation of asphalt in ethanol at ablation speeds of (100, 75, 50, 10 mm/s). The morphology, composition and optical properties of the synthesized samples were studied experimentally using FESEM, HRTEM, EDS, and UV-vis spectrophotometer. Results showed that the band gap energy decreased with decreasing the ablation speed (increasing the ablation time), the minimum mean particle size of the synthesized samples was 76 nm at an ablation speed of 100mm/s, while the maximum mean particle size was 98 nm at ablation speed of 50 mm/s, the nanospheres were agglomerated to form larger spherical nanoshapes. All the synthesized carbon nano colloids exhibited a blue-green PL emission. It was concluded that the presence of carbon nanorods has an effect on the optical properties of the synthesized nanospheres.

Structural characteristics and effective two photon absorption induced optical limiting behavior of Co2+ doped monoclinic LaPO4 nanostructures

The Nonlinear optical limiting properties of pure and Co2+ doped monoclinic LaPO4 nanostructures synthesized by co-precipitation technique is reported. The Structural confirmation of Co2+ doped LaPO4 nanostructures is studied by X-ray diffraction (XRD) and Raman spectra. The replacement of larger La3+ ion by smaller Co2+ ion is confirmed by the shift of XRD and Raman scattering lines. X ray photoelectron spectroscopy (XPS) survey spectrum of 0.3 % Co2+ doped sample confirms the presence of lanthanum (La). Phosphor (P), oxygen (O) and Cobalt (Co) elements. Transmission electron microscopy (TEM) image portrays the formation of nearly mono-dispersed spherical particle with diameter of 48 nm. The absorption spectra reveals a blue shift in absorption edge with additional peak at 580 nm upon Co2+ doping. Photoluminescence emission spectra shows blue green emission with major peak at 440 nm. Open aperture (OA) Z-scan technique excited at 532 nm with a nanopulsed Nd: YAG laser revealed pure and Co2+ doped LaPO4 exhibits reverse saturable absorption ascribed due to two photon absorption (2PA). Intensity dependent OA measurements shows that the nonlinear absorption coefficient remains constant with varying input on-axis intensity, ensuring genuine 2PA for pure sample. While for Co doped sample, the nonlinear absorption coefficient varies with input on-axis intensity, assuring the occurrence of sequential 2PA. Co doped samples exhibit enhanced nonlinear absorption due to synergistic influence of Co2+ in LaPO4 crystal structure. Optical limiting action induced by 2PA in LaPO4 with lower onset limiting ensures the potentiality of the chosen material for photonic applications.

Interstitial Zinc Boosted Light Tunability, Afterglow, and Ultrabright White Emission in Zinc Germanate (Zn2GeO4)

To reduce the burden of solid-state lighting and phosphor-converted light-emitting diode technologies on rare earth (RE) and avoid their potential supply risks, we have developed a RE-free Zn2GeO4 (ZGeO) microcrystalline phosphor. It was synthesized by a simple and scalable solid-state reaction of ZnO and GeO2 at 1200 °C. High-temperature synthesized ZGeO demonstrated color tunable emission from bluish-white to green on changing the excitation wavelength from 265 to 335 nm with a photoluminescence quantum yield of 42 and 9%, respectively. They could also convert highly energetic X-ray to bluish-green light emission. First-principles calculations showed that bluish-white and green light emissions are linked to zinc interstitials present, respectively, in zinc (Zni2) and zinc–germanium rings (Zni1). These defects generated in large numbers via high-temperature annealing along with antisites boosted the generation of trapping centers leading to dual persistent luminescence (PerL) of white and green light for more than 60 min as well as exhibited radioluminescence. Luminescent ink based on ZGeO was fabricated and successfully tested for anticounterfeiting applications. An extra effort has been vested on making this solid-state processed ZGeO dispersible in water-soluble deep eutectic solvent which could be a game changer for its marketability. This material has great potential to become an efficient RE and dopant-free phosphor synthesized by a simple, scalable, and cost-efficient route for applications in solid-state lighting, display, and anticounterfeiting, having multifunctionalities such as PerL, tunability, and RL.

Manganese and Iron Doped Cadmium Gallate Spinel as a Multifunctional Inorganic Material

Manganese and iron doped cadmium gallate has been synthesized by sol–gel approach. PXRD pattern shows the cubic arrangement of cadmium gallate spinel. Raman spectrum concludes the complete structural analysis of undoped and doped samples. Additionally, morphology and elemental ratio is obtained using FESEM and EDS spectroscopy. Blue indigo and green emission bands are shown in photoluminescence spectra. An excellent antiferromagnetic and ferromagnetic behavior of manganese and iron doped cadmium gallate are shown in the magnetic study. Low band gap of doped samples has made this material as a prominent catalyst for the degradation of methylene blue dye when exposed to UV–visible irradiation.

Aqueous degradation and atomic layer deposition (ALD) stabilization of BaAl2O4: Eu2+, Dy3+ long afterglow phosphors

This paper presents the aqueous degradation mechanisms of BaAl2O4:Eu2+, Dy3+ phosphors and demonstrates an ability to prevent degradation via Al2O3 nano encapsulation of powders by atomic layer deposition (ALD) technique. Phosphor powder is synthesized from the solid-state reaction method. The aqueous degradation of this phosphor is systematically studied. This phosphor is found to hydrolyze and degrade within just 30 min of exposure in water. The degradation of BaAl2O4 host lattice directly affects the blue-green light emission at 497 nm, producing blue- and red-emissions that are peaked at 429 nm and 687 nm, respectively. Hydrated and structural decomposed BaAl2O4 reveals a continuous change in the phase assemblage over 30 days of immersion. To prevent this rapid degradation, use of a protective nanocoating was investigated. 10 nm Al2O3 coatings were applied to the surface of the phosphor powder via ALD. ALD coated BaAl2O4:Eu2+,Dy3+ phosphor retains its phosphorescence for at least 7 days of water exposure. Successful encapsulation of such phosphor particles will make them possible to use in aqueous applications or store in long-term humid environments.

Structure and luminescence properties of Cu+ doped glasses prepared by ion exchange

Doped Cu+ glass was prepared by ion exchange method. It was found that the accumulation zone of copper ions would be formed on the glass surface during the process of ion exchange, and there was an extreme point of copper ion distribution concentration about 10 µm inside the glass surface after ion exchange. The exchange depth of copper ions in the sample increased with the increase of ion exchange time. At low ion exchange temperatures, the Cu elements exchanged into the vitreous body exists in the form of Cu+ and Cu2+. With the exchange of Cu+ into the glass, the degree of polymerization of the glasses continued to increase. By raising the ion exchange temperature, a large number of spherical Cu2O grains formed on the surface of the sample, continuing to raise the temperature, these spherical grains agglomerated and adhered to form lamellae structure, mainly composed of oxides of Cu2O and CuO. The PL spectra showed that the ion-exchanged glass exhibited broadband blue-green emission light with a central wavelength of 468 nm and half-height width of 154 nm under 290 nm excitation. The luminescence intensity appeared to increase firstly and then decrease with increasing the ion exchange time. Dispersed spherical Cu2O grains were generated on the surface of the sample exchanged at 410 °C for 16 h. Co-composite luminescence of the spherical Cu2O semiconductor and the Cu+ doped in the glass effectively increased the luminescence intensity of the samples. In addition, the samples showed a favorable thermal stability of luminescence.

Cationic Zinc(II) Complexes with Carbazole-Type Counter-Anions: Intracomplex Donor/Acceptor Pairs Affording Exciplexes with Thermally Activated Delayed Fluorescence.

Two cationic zinc(II) complexes with carbazole-type counter-anions, namely, [Zn(tpy)2]2+[CAZ-p-BF3-]2 (Zn-p) and [Zn(tpy)2]2+[CAZ-o-BF3-]2 (Zn-o), have been designed and synthesized, where tpy is 2,2':6',2″-terpyridine, CAZ-p-BF3- is 4-((9H-carbazol-9-yl)phenyl)trifluoroborate, and CAZ-o-BF3- is (2-(9H-carbazol-9-yl)phenyl)trifluoroborate. The complex cation [Zn(tpy)2]2+ (as the acceptor) and the carbazole-type counter-anion CAZ-p-BF3- or CAZ-o-BF3- (as the donor) form an intracomplex donor/acceptor pair. Single-crystal structures reveal that compared to Zn-p, Zn-o exhibits a stronger π-π stacking interaction between the carbazole group (as the donor unit) of the counter-anion and the tpy ligand (as the acceptor unit) of [Zn(tpy)2]2+ because of the different anchoring position of the BF3- anion in the counter-anion. In a doped film, Zn-p and Zn-o afford an isolated exciplex formed between the carbazole group and the tpy ligand within the single complex, which gives green-yellow emission with a thermally activated delayed fluorescence (TADF) feature. In crystalline states, Zn-p and Zn-o afford exciplexes with blue emission centered at 468 nm and green-blue emission centered at 508 nm, respectively. The Zn-p crystalline sample shows a relatively large singlet-triplet energy gap (ΔEST) (0.33 eV) and no TADF, whereas the Zn-o crystalline sample exhibits a small ΔEST (0.06 eV) and distinct TADF, with a reverse intersystem crossing rate at 3.3 × 105 s-1. Zn-p and Zn-o both exhibit intriguing mechanochromic luminescence, with largely red-shifted (by over 70 nm) emission and modulated TADF properties upon mechanically grinding the crystalline samples. The work demonstrates that donor/acceptor pairs affording exciplexes can be formed within cationic metal complexes using counter-anions with donor nature, which opens a new avenue toward photo-active metal complexes with rich photophysical properties.

Influence of implantation assisted Ni doping on structural and optical properties of WO2.72 films

In this paper, structural and optical properties of WO2.72 thin films implanted by 150 keV Ni ions having ion fluences in the range of 1015 to 1016 ions/cm2 have been investigated. Structural investigations (Raman and XRD) suggest the formation of the crystalline monoclinic phase of pristine films. However, after ion implantation, the crystalline quality degrades as a function of ion fluences, and complete amorphization is observed at highest fluence. Further, the bandgap decreases upon ion implantation as a result of band tailing effect. Optical investigation under UV excitation delineates the existence of NUV, band-to-band transition and blue green emission bands in WO2.72 thin films. Implantation-assisted Ni doping blueshifted the new NUV emission peaks due to the enhancement in free electron concentration in the conduction band (CB). The overall hue of the emitted light investigated using Commission International de l’Eclairage (CIE) diagram demonstrates the transition from light to deep blue region upon Ni implantation.

Blue emission: Optical properties of Co2+ doping towards Zn2SiO4 glass-ceramics

This article reports the fabrication of Zn2SiO4:Co2+ using composition (Co3O4)y[(ZnO)55.0(WRHA)45.0]1−y where y = 0.0, 0.01, 0.05 and 0.10 wt. % via melt and quenching technique. The effect of Co3O4 concentration dopant towards willemite also reported as in their physical characteristics, UV–visible, optical bandgap, and photoluminescence spectroscopy. The samples of Zn2SiO4:Co2+ became bluer as the dopant increased which imply the incorperation of Co2+ towards the willemite lattice and the density increasing from 3.1472 to 3.4592 gcm−3 when the dopant increased. XRD results showed presence of the stable state of willemite phase, α-Zn2SiO4 after sintered at 950 °C. In addition, there appeared two absorptions spectra in the optical absorption. First is the triply split absorption band centred at 475–700 nm spectral range assigned to 4A2 → 4T1 (4P) spin allowed optical transition of Co2+ ions whilst second absorption centred at ∼325 nm assigned to scattering by the Zn2SiO4. The optical bandgap decreases first as the dopant was introduced, then increased at highest value of Co3O4 concentration dopant. The PL spectra showed the undoped-Zn2SiO4 (sample B1) emits nine minor peaks in the blue, green, and yellow region centred at 382, 395, 415, 443, 460, 469, 482, 511 and 532 nm then, when Co3O4 was introduced, the Zn2SiO4:Co2+ presents five peaks correspond to blue emission (∼420 nm, ∼444 nm, ∼461 nm and ∼485 nm) and green emission (∼525 nm). Lastly, the CIE 1931 chromaticity showed all sample fall in the blue region which support the PL spectra and proves the possibility to produce blue emissions.

Effect of Hydrothermal Reaction Temperature on Fluorescent Properties of Carbon Quantum Dots Synthesized from Lemon Juice for Adsorption Applications

Photoluminescent carbon quantum dots (CQDs) were synthesized from lemon juice precursors via single-step, hydrothermal techniques under different temperatures to control the optical properties. The synthesized CQDs were characterized by PL, illuminated UV analyzer chamber, UV–vis spectroscopy, X-ray diffractometer, Fourier-transformed infrared spectrophotometry, and zeta potential techniques. The results show that the synthesized CQDs had an excellent blue–green emission extending up to the infrared region with high quantum yield (Φ) in the range of 14%–41%. The effect of reaction temperature and the aging of CQDs on the emission spectra of CQDs are also investigated. Furthermore, the adsorption effect of the synthesized CQDs was evaluated on methylene blue (MB) dyes. The result indicated the synthesized CQDs have excellent adsorbent properties with a removal efficiency of 60%–82% and an extremely fast adsorption rate of 6 × 10−2 min−1 for MB dyes.

Study on the luminescence characteristics of Tb3+-doped TeO2-Bi2O3-BaF2 glass for blue-green laser emission

In this study, we prepared Tb3+-doped bismuth tellurite glasses by a high-temperature melting method. The matrix glass was characterized by higher thermal stability (ΔT = 102 °C) and lower maximum phonon energy (614 cm−1). Based on absorption spectra, Judd-Ofelt analysis revealed the spontaneous radiation transition probability (269.34 s−1) and fluorescence branching ratio (41.55%) of 5D4→7F5 transition. The luminescence peaks of the samples were located at 486 nm and 545 nm blue-green bands. Meanwhile, the luminescence intensity increased with the increase of Tb3+ concentration and reached the maximum at 4mol% Tb4O7. In addition, emission cross-section and gain coefficients were calculated in blue wavelength range, the maximum values were 2.01 × 10−22 cm−1 and 2.92 cm−1, respectively. Combining all the above results, Tb3+ doped bismuth tellurite glass had potential application value in the field of blue-green communication.