Blue Emission Band Research Articles

Nanocrystalline gadolinium doped ZnO: An excellent photoluminescent material and efficient photocatalyst towards optoelectronic and environment remedial applications

Simple wet-chemical method of synthesis was adopted for the preparation of Gd doped ZnO nanoparticles along with pristine ZnO aiming towards the improvisation of photoluminescence (PL) and photocatalytic (PC) properties of ZnO by rare earth doping. X-ray diffraction measurement reveals the formation of wurtzite ZnO without any impurity phases related to the Gd dopants. Effective increase in the crystallite size of ZnO has been observed with Gd doping along with microstrain increment as obtained from the XRD results. A notable change in the particle morphology of ZnO is also noticed from FESEM study as Gd ions are incorporated into ZnO lattice. FTIR spectra indicate the formation new bands linked with Gd–O in the doped samples along with Zn–O bonds. Absorbance study in UV–Vis region exhibits a decrease in ZnO band gap as Gd ions are incorporated. Gd doping introduces shallow energy levels in the band gap resulting the shrinking of band gap. PL measurement shows an enhancement in the blue emission band with the introduction of new orange-red emission initiated by Gd doping. Photocatalytic measurement shows that the Gd-ZnO sample demonstrates better degradation efficiency in degrading organic dyes like methyl orange and methylene blue as compared to pure ZnO. Doping of Gd ions results in a better charge separation efficiency and suppression in carrier recombination which leads to such enhanced photodegradation efficiency. Gd-ZnO samples display the quality of being highly stable after fourth cycle of degradation hence can be used for treating industrial waste materials in an effective manner.

Correlating yellow and blue luminescence with carbon doping in GaN

Blue and yellow emission bands in carbon-doped GaN grown by MBE were investigated in low-temperature cathodoluminescence measurements performed in a scanning transmission electron microscope (STEM-CL) with high spatial resolution. Blue luminescence at 2.85 eV and two contributions in the spectral range of the yellow emission band around 2.2 eV separated by 120 meV are observed in carbon-doped material, whereas only one distinctive yellow luminescence contribution was found in unintentionally-doped GaN.

Tunable multicolor luminescence and energy transfer mechanism in Eu3+/Dy3+ co-doped Ca2Sb2O7 phosphor under UV excitation

A series of Ca(2-x-y)Sb2O7:xDy3+,yEu3+ phosphors with tunable multicolor luminescence were synthesized via solid-state reaction method. The XRD, EDX and HR-TEM analysis confirmed the phase purity and the crystallinity of the samples. Under ultraviolet (UV) excitation, Ca(2-x-y)Sb2O7:xDy3+,yEu3+ phosphors exhibit characteristic emission bands of both Dy3+ and Eu3+ ions, along with an intense blue emission band of the host. The emission peaks at 575 and 660 nm correspond to 4F9/2 →6H13/2 and 4F9/2 →6H11/2 transitions of Dy3+ ions, and the peaks at 528 and 612 nm originate from 5D1 →7F1 and 5D0 →7F2 transitions of Eu3+ ions, respectively. There exists efficient energy (ET) transfer from host to Eu3+/Dy3+ ions, as well as from Dy3+ to Eu3+ ions. The decay lifetime of host and Eu3+/Dy3+ emissions were calculated to be in the microsecond range. By properly modulating the concentration of Eu3+/Dy3+ ions, the CIE chromaticity coordinates of the samples vary from (0.144, 0.097) to (0.446, 0.312). Hence, multicolor emission which can be tuned from blue to bluish-white and eventually to reddish-white can be obtained in the warm CCT region. The results indicate that Ca2Sb2O7:Dy3+,Eu3+ phosphor could be a promising candidate for UV excited WLEDs and multicolor displays.

Evaluating Street Lighting Quality in Residential Areas by Combining Remote Sensing Tools and a Survey on Pedestrians’ Perceptions of Safety and Visual Comfort

The perceived quality of street lighting influences pedestrians’ perceptions of safety and visual comfort, as well as outdoors activities at night. This study explores the association between street lighting attributes, such as illuminance and wavelength, and pedestrians’ feeling of safety (FoS) and perceived lighting quality (PLQ) in eight residential districts in Dalian, China. To achieve this goal, we combine remote sensing technology with ground investigation. The ground research includes physical measurements of lighting attributes, such as intensity, color temperature, and glare, as well as survey evaluations of pedestrians’ perceptions of safety and visual comfort. We also analyze the influence of several environmental factors, such as traffic volumes and vegetation, while accounting for personal characteristics of the observers, such as gender and age. Findings from the remote sensing reveal that Dalian’s residential districts differ substantially by their nighttime light emissions, with high concentration of strong red band (i.e., long wavelength) emissions occurring in Zhongshan and Jinzhou, and strong blue band (i.e., short wavelength) emissions found in central Zhongshan. Results from the ground surveys further indicate that a satisfactory level of FoS reaches at the illumination levels of 5–17 lx, and that people feel safer if nighttime light is warm and uniform. From a multiple regression analysis, it is also found that illuminance and uniformity are the main factors affecting PLQ under conditions of low or high illuminance, while glare and color temperature play a more significant role under high illuminance. In addition, a satisfactory level of PLQ is found at illuminance levels of 25–35 lx and light color temperature of 4000 K–5500 K.

Sensitive optical thermometer via efficient energy transfer in dual-emitting thermochromic YNbO4:Bi3+, Eu3+ phosphor

The remote and non-invasive optical thermometer exploiting fluorescence intensity ratio technology is of great importance in various intelligent optoelectronic sensors. Dual-emitting YNbO4:Bi3+, Eu3+ phosphor is synthesized and investigated for the development of temperature sensing materials. The phosphor excited at 318 nm shows a blue broad band emission and several red sharp peaks. The value of Bi3+→Eu3+ energy transfer can reach 98.2% when Eu3+ doping content is 0.14. Benefiting from diverse thermal response behaviors due to Bi3+ and Eu3+ ions completely different electronic configurations, a dual-emitting optical thermometer is designed. The maximum values of absolute and relative sensitivities are as high as 2.51% K−1 at 473 K and 1.43% K−1 at 423 K, respectively. The thermochromic phosphor possesses a great chromaticity shift (ΔE = 317×10−3) with temperature. Based on superior color discriminability, visual colorimetry temperature measurement relied on thermal characteristic is proposed. All the results demonstrate that YNbO4:0.01Bi3+, 0.005Eu3+ phosphor as a sensitive and reliable optical thermometer has great potentials in temperature measurement.

Luminescence properties of Yb3+ and Er3+ co-doped into Gd2O3:Bi3+ phosphor powder

Yb3+ and Er3+ co-doped Gd2O3:Bi3+ phosphor were prepared via a combustion method. The structural properties and surface morphology of the phosphors were studied with X-ray diffraction and a scanning electron microscope. UV–visible absorption, photoluminescence and cathodoluminescence (CL) spectra were also investigated. The optical bandgap of Gd2O3 increased with additional doping. The visible emission confirmed that the Gd2O3:Bi3+ co-doped with Yb3+ is located in the blue and green band regions related to the Bi3+ in the S6 and C2 symmetry sites. The near-infrared (NIR) down-conversion (DC) emission intensity increased upon increasing the Yb3+ concentration. The visible Bi3+ emission was reduced when adding a higher Yb3+ ion concentration while the NIR emission increased due to the energy transfer from the Bi3+ to the Yb3+ ions. UV-Vis energy excitation photons were successfully converted into NIR photons. The up-conversion (UC) visible emission spectra of Gd2O3:Bi3+ co-doped Er3+ consisted of two strong green, weak red and NIR emission bands. The 980 nm infrared excitation was successfully converted into UV-Vis emission. The CL emission spectra confirmed blue emission bands assigned to the 3P1 → 1S0 transitions of the Bi3+ ions and the green-yellow emission bands corresponded to an overlap between the 3P1 → 1S0 transitions of the Bi3+ ions and the 2H11/2, 4S3/2 → 4I15/2 transitions of the Er3+ ions. A significant enhancement of the emission intensities of Yb3+ and Er3+ ions was observed after Bi3+ doping. The results indicated that Gd2O3 materials based on the Bi3+–Yb3+ and Bi3+–Er3+ couples may be possible phosphors for improving photovoltaic conversion efficiency via spectral modification utilizing the DC and UC processes.

Syntheses, crystal structures and properties of three compounds based on the dicarboxylate ligand with S-S flexible linkage

Three new compounds, [MnL(2, 2΄-bipy)2]n·1.5nH2O (1), Co(4, 4ˊ-bipy)(H2O)4·2HL (2) and 2HL·(4, 4ˊ-bipyH)·2H2O (3) (H2L = 2,2΄-dithiosalicylic acid, 2, 2΄-bipy = 2, 2΄-bipyridine, 4, 4΄-bipy = 4, 4΄-bipyridine), have been synthesized by hydrothermal and evaporation methods. Structural determination reveals that compound 1 shows a one-dimensional chain structure with L2- ligands adopting bridging coordination modes, compound 2 features a mononuclear structure with uncoordinated HL- anions, balancing the charges, compound 3 is a new inclusion compound of HL- anions and 4, 4ˊ-bipyH cation with π-π stacking interactions. In compounds 1-3, the flexible S-S linkages can make H2L ligands present different conformations of dihedral angles between the terminal benzene rings. The S-O hypervalent bonds can stabilize the conformations. Thermogravimetric analyses and fluorescent measurements of compounds 1 and 2 have been performed. Compounds 1 and 2 exhibit broad blue fluorescent emission bands at 420 nm and 424 nm, respectively.

Blue luminescence origin and Mg acceptor saturation in highly doped zinc-blende GaN with Mg

We study the incorporation of Mg at degenerated doping concentration in zinc-blende GaN and its effect on the optical and electrical properties. The study starts with a theoretical analysis by Density Functional Theory (DFT) and then supported by an experimental methodology employing X-Ray Diffractometry (XRD), Atomic Force Microscopy (AFM), Photoluminescence (PL), Hall effect, Secondary Ion-Mass Spectroscopy (SIMS), and X-Ray Photoelectron Spectroscopy (XPS). Employing Ga-rich growth conditions allow providing the amount of Mg able to obtain an Mg-acceptor concentration limit above 2 × 1019 cm−3. Moreover, the blue band emission centered at 2.85 eV is discussed and used as a systematic tool to detect the Mg incorporation into an undesired site. To the best of our knowledge, the blue emission mechanism is consistently explained in zb-GaN:Mg for the first time by theory and experimentation.

Tailored TiO2 nanorod arrays for dye sensitized solar cell applications

A TiO2 layer using titanium (IV) butoxide on fluorine doped tin oxide (FTO) substrate is used as a seed layer for the growth of TiO2 nanorod arrays (TRA). TRAs with length of ∼1 to 2 μm were grown on seed layer (SL) by two step method. In the first step TiO2 SLs were deposited by sol-gel assisted spin coating method and the second step involved the typical hydrothermal technique to grow rutile TRAs. Most of the TRAs grown on FTO substrate without SL were randomly oriented and TRAs with 0.025 M SL was oriented vertically from the substrate. Whereas TRAs grown on 0.05 M SL showed hierarchical nanoflower clusters composed of a bunch of TRAs as petals blooming from the core. The XRD pattern showed all the three TRAs to be crystallized in a tetragonal rutile phase. Photo luminescence spectra revealed that the TRAs on 0.05 M SL have comparatively low intense blue emission band, predicting the suppressed electron-hole recombination rate. The power conversion efficiency of the dye sensitized solar cell (DSSC) with TRAs grown on 0.05 M SL was recorded as 3.18%, which is 3 times greater than that without SL and 1.6 times greater than that with 0.025M SL in our observations.

Dual-mode optical thermometry based on Bi3+/Sm3+ co-activated BaGd2O4 phosphor with tunable sensitivity

A series of the BaGd2O4:Bi3+, Sm3+ phosphors with dual emission centers were prepared by high-temperature solid-phase method. X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, fluorescence spectroscopy, lifetime decay curve, and variable temperature emission spectroscopy were used to systematically study the structure, luminescence performance, and temperature characteristics of the samples. At ultraviolet stimulation, BaGd2O4:Bi3+, Sm3+ phosphors exhibit broad band blue emission, corresponding to the transition of Bi3+ from 3P1 level to 1S0 level, and sharp red characteristic emission, corresponding to the Sm3+ ions’ energy level transition from 4G5/2 to 6Hm/2(m = 5,7,9). In addition, the Bi3+ and Sm3+ ions’ emission positions in BaGd2O4 host are ideally separated. Based on the property, FIR can be employed to test the difference of temperature in response to performances between Bi3+ blue light emission and Sm3+ red light emission. For the Bi3+/Sm3+ co-doped system, it is found that their relative sensitivity gradually decreases with the increase of the Sm3+ ion concentration, the value of maximum can reach 1.105%K−1, which makes it possible to synthesize temperature sensing materials with adjustable sensitivity. The relative sensitivity can also be calculated by experiments related to the decay lifetime, and the value of maximum obtained was 1.662%K−1. Thus, BaGd2O4:Bi3+, Sm3+ systems are superior non-contact optical pyrometer materials with ultrahigh temperature sensitivity and superhigh signal discriminability.

Fluorescent hydrogel of chitosan and gelatin cross‐linked with maleic acid for optical detection of heavy metals

AbstractA multi‐component, fluorescent hydrogel of chitosan and gelatin using maleic acid as a cross‐linking agent was fabricated with improved mechanical and thermal properties. The FTIR spectroscopy and SEM studies confirmed the formation of a cross‐linked and porous hydrogel. The XPS studies confirmed the presence of rich functionalities over the surface of hydrogel. The hybrid hydrogel possessed strong blue emission band centered at 438 nm when excited with an absorption band centered at 384 nm. The fluorescent hydrogel was tested for selective detection of different heavy metal ions including Cr (VI) in the aqueous solution. The strong complexation among the functional groups of hydrogel and metal ions led to the quenching of hydrogel's fluorescence. The fluorescence of hydrogel was quenched significantly in the presence of Cr (VI) ions in comparison to the other heavy metal ions. The fluorescence‐quenching efficiency displayed a linear response to the Cr (VI) concentration in the range of 1–14 nM with a lower detection limit of 0.12 nM. Embraced with good sensitivity and selectivity for Cr (VI) ions, the solid hydrogel with stable fluorescent properties holds a great potential in chemical sensing applications.

Photoluminescence properties, excellent thermal stability and energy transfer in Ce3+ and Tb3+ co-doped Sr3Gd2(BO3)4 phosphors

Sr3Gd2(BO3)4: Ce3+, Sr3Gd2(BO3)4: Tb3+ and Sr3Gd2(BO3)4: Ce3+, Tb3+ phosphors were synthesized through conventional high temperature solid state reaction method. Phase purity, crystal structure, photoluminescence properties, and lifetime of the samples were analyzed in detailed. Sr3Gd2(BO3)4: Ce3+ showed a bright blue broad emission band, which was attributed to 4f → 5d transitions of the Ce3+ ions, and it exhibited two broad excitation ranged from 200 nm to 400 nm. For all Sr3Gd2(BO3)4: Tb3+ samples, under ultraviolet excitation bands of 240 nm, four emissions peaked at 490 nm, 544 nm, 585 nm and 623 nm appeared, due to the 5D4 → 7FJ (J = 6, 5, 4, 3) transitions of Tb3+ ions. For the Sr3Gd2(BO3)4: Ce3+, Tb3+ phosphors, the lifetime of the samples were analyzed, which showed the presence of energy transfer between the Ce3+ and Tb3+. The energy transfer efficiency from Ce3+ ions to Tb3+ ions reached 98.37%. When the temperature reached 443 K, the luminescence intensity reached 88% of the initial value. Finally, a white LED was fabricated by using a 365 nm near ultraviolet LED chip combined with BaMgAl10O17: Eu2+ (blue), Sr3Gd0.91(BO3)4: 0.09Ce3+, 1.0 Tb3+ (green), and CaAlSiN3: Eu2+ (red) phosphors. The color coordinates was (0.40, 0.42); correlated color temperature was 3721 K; color rendering index was 91.1. The results showed that the Sr3Gd2(BO3)4: Ce3+, Tb3+ green phosphors were suitable for white LEDs.

Dual-Emitting Carbonized Polymer Dots Synthesized at Room Temperature for Ratiometric Fluorescence Sensing of Vitamin B12.

Ratiometric fluorescence (FL) probes are highly desirable for highly sensitive and reliable assays. Dual-emitting carbonized polymer dots (CPDs) have great application prospects in building ratiometric FL sensors. However, dual-emitting CPDs are usually synthesized at high temperatures and high pressures, which not only increases the cost but also complicates the structure of CPDs. Here, we developed a facile strategy for the fabrication of dual-emitting CPDs at room temperature using tetrachlorobenzoquinone and ethylenediamine. The formation of CPDs was induced by Schiff base condensation reaction, enabling the following cross-linking polymerization process. The dual-emitting CPDs demonstrate good photostability and antioxidant capacity. Importantly, the typical dual-emission bands of the as-prepared CPDs are found to have a blue emission band at 445 nm with a maximum excitation of 350 nm and a yellow emission band at 575 nm with a maximum excitation of 440 nm. Based on the dual-emitting property of CPDs, a ratiometric FL nanoprobe is obtained for sensitive determination of vitamin B12 (VB12), as the inner filtering and static quenching effects between VB12 and CPDs allow effective quenching of the blue FL of CPDs, while the yellow FL is maintained. The established assay shows linear detection ranges of 0.25-100 μM with a low limit of detection of 0.14 μM. These findings provide new guidance for the facile preparation of CPDs with excellent dual-emitting optical properties, indicating good prospects in biosensing.

Bis(N-naphthyl-N-phenylamino)benzophenones as exciton-modulating materials for white TADF OLEDs with separated charge and exciton recombination zones

Organic semiconductors were employed as exciton modulators, blue emitters, hole-transporting materials and hosts with resonant-appropriate singlet and triplet energies for efficient and stable white organic light emitting diodes (OLEDs). Two 4,4'-bis(N-naphthyl-N-phenylamino)benzophenones were synthesized using isomeric N-naphthyl-N-phenylamines as the donors and benzophenone as the acceptor moiety. Molecular design of new compounds allowed to obtain required combination of properties, i.e. blue prompt fluorescence in solid state with singlet energies close to those of the selected blue emitter exhibiting thermally activated delayed fluorescence (TADF), low triplet energies of 2.32 and 2.45 eV which are close to those of orange TADF emitter, good charge injecting properties (ionization potentials of 5.68 and 5.79 eV), good charge transporting properties with hole mobilities exceeding 10−4 cm2 (V s)−1 and high thermal stability with five percent weight loss temperatures up to 428 °C. The blue-emitting compounds were used as exciton modulators between the known blue and orange TADF emitters for fabrication of white OLEDs exploiting spatial exciton allocation strategy. In the frame of this strategy, resonant energy transfers: NPABP emitters → blue TADF and NPABP emitters → orange TADF emitters were investigated using different device structures towards efficient white electroluminescence. About twice higher external quantum efficiency was obtained for devices with two resonant energy transfers in comparison to that of the reference devices with one resonant energy transfer proving efficiency of spatial exciton allocation strategy for white TADF OLEDs. The best quality of white electroluminescence is characterized by CIE coordinates of (0.32, 0.31), colour temperature of 4490 K and colour rendering index of 80. Similar stability of blue and orange emission bands in white electroluminescence spectra was achieved due to the separation of charge and exciton recombination zones in the device structure.

Tunable luminescence and energy transfer mechanism of Ca2Sb2O7:Dy3+ host sensitized single phase cool white light emitting phosphor

Tunable white light-emitting Ca(2-x)Sb2O7:xDy3+ phosphors were synthesized via high temperature solid-state reaction method. The crystal structure, morphology, luminescence characteristics, and energy transfer mechanism of the phosphors were investigated using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), high resolution transmission electron microscopy (HR-TEM), UV–Visible spectroscopy, photoluminescence (PL) spectroscopy, and Fluorescence lifetime analysis. The XRD, EDS, and TEM analysis confirmed the phase purity and orthorhombic weberite structure of the samples with an average particle size in the range of 0.2 to 0.3 ​μm. Under ultraviolet (UV) excitation of 330/351 ​nm, the prepared phosphors exhibit characteristic emission bands of Dy3+ ions along with the blue emission band of the host. The broad band peaking at 440 ​nm corresponds to Sb5+ to O2− transition of host and the peaks at 477, 575, and 670 ​nm originates from 4F9/2 ​→ ​6H15/2, 4F9/2 ​→ ​6H13/2 and 4F9/2 ​→ ​6H11/2 transitions of Dy3+ ions respectively. There exists efficient energy transfer from Ca2Sb2O7 host to Dy3+ ions and the energy transfer efficiency increases with an increase in Dy3+ ion concentration. Using Dexter’s theory, the mechanism of energy transfer was found to be dipole-quadrupole interaction and the energy transfer process is explained in detail. The decay lifetime of Dy3+ ions was estimated to be in the microsecond range. The critical distance for concentration quenching is determined to be 13.807 ​Å and the dominant mechanism is dipole-dipole interaction. The calculated Commission International de L’Eclairng (CIE) coordinates and correlated color temperature (CCT) values imply that the emission color can be tuned from blue (0.144, 0.097) to near-white (0.296, 0.292) in the cool CCT region. The results suggest that Dy3+ doped Ca2Sb2O7 phosphor is a potential candidate for solid-state lighting and display fields.

Improving red afterglow properties of CaZnGe2O6: Mn2+ by co-doping Bi3+

Bi3+, Mn2+ co-doped CaZnGe2O6 red long afterglow materials were prepared by high temperature solid state reaction method. The phosphor has broad excitation band ranging from 220 nm to 350 nm with two peaks at 255 nm and 300 nm and can give blue, green and red emission band peaking at 448 nm, 530 nm and 645 nm, respectively. Due to the emission properties of Bi3+ ions and the Bi3+→Mn2+ energy transfer, the co-doped Bi3+ ions can not only enhance the PL luminescence of the phosphor, but also adjust the emission color. After irradiation of 300 nm ultraviolet light, the phosphors exhibits long-persistent red phosphorescence. Thermoluminescence tests demonstrate that the introduction of Bi3+ ions can increase the trap depth and trap concentration, greatly improving the afterglow time and brightness of the CaZnGe2O6: Mn2+ phosphor. The present work might provide reference for designing new rare earth free red long afterglow materials.

A systematic investigation on structural and optical properties of sol–gel spin coating fabricated CdS nanocrystalline thin films: effect of Ni doping

In the present work, we have successfully fabricated undoped and Ni-doped nanocrystalline CdS thin film on an ultrasonically cleaned glass substrate employing the sol–gel spin coating technique. The structural and spectroscopic properties of the films were investigated using XRD spectra, UV–Vis spectroscopy and photoluminescence spectra, respectively. The X-ray diffraction spectra revealed the polycrystalline nature of films with cubic structure and (111) as preferred orientation. The average crystallite size evaluated by the Debye–Scherrer formula lying in the range of 6–12 nm for the deposited films. According to UV–VIS Spectroscopy, the average transmittance of films in the visible region varies between 70–90%. The optical band gap of CdS thin film was evaluated from absorption spectra. The bandgap of the deposited films is in the range of 2.48–2.70 eV which is higher than that of bulk CdS (2.42 eV). This verifies the blue shifting in band edge of CdS nanocrystalline thin films due to the quantum confinement effect. Photoluminescence spectra of the thin film showed that the fundamental band edge emission peak centred at 485 nm also called blue band emission. It is observed that the low temperature resistivity of the films was in the range of 107–103 Ω cm and also found to decrease with increasing Ni concentration, as a result from dc two probe measurements.

Synthesis of silicon quantum dots using chitosan as a novel reductor agent

In the present paper we report a novel synthesis method of silicon quantum dots (SiQDs) using 3-Aminopropyltriethoxysilane (APTES) as silicon precursor and low molecular weight chitosan (CS) as reducing agent. The obtained SiQDs have a hydrodynamic diameter of 2.3 nm, water dispersible, presents blue emission band at 434.5 nm (2.85 eV) with a Commission Internationale de l’Eclairage 1931 (CIE1931) chromaticity coordinates (x = 0.1665, y = 0.1222), the experimental absorbance of the SiQDS was measured and the band gap (Eg) was estimated through PerkinElmer’s method, the obtained value was 3.1 eV and a positive ζ-potential of + 35 mV, resulting in photonics, microelectronics, and biotechnological potential applications.

Bismuth activated blue phosphor with high absorption efficiency for white LEDs

Trivalent bismuth (Bi3+) activated blue-emitting materials have attracted considerable attention because they effectively avoid the reabsorption demerits compared to traditional rare earth activators. Unfortunately, these materials are often plagued by mismatch to the near-ultraviolet (n-UV) chip and short blue emission peak as well as low n-UV absorption efficiency. In this work, we successfully designed a blue-emitting phosphor SrZnSO:Bi3+ with a wide n-UV excitation band ranging from 310 to 400 nm and an ideal blue emission band centered at 460 nm. Furthermore, SrZnSO:0.03Bi3+ phosphor exhibits an extraordinary absorption efficiency of 73.21% ascribed to the intense absorption of the matrix and Bi3+ in the n-UV region. The relationship between the excitation peak position of Bi3+-related phosphors and the size of the polyhedron were also summarized. A white light-emitting diode (WLED) was fabricated using a 370 nm n-UV chip, the composition-optimized sample SrZnSO:0.03Bi3+ and the commercial phosphors. Interestingly, the temperature-sensitive luminescence behavior is beneficial to the performance improvement of the WLED. The WLED demonstrates a warm white light whose Commission Internationale de L′Eclairage (CIE) coordinates are (0.3817, 0.3885), outstanding color rendering index of 93.4 and low correlated color temperature of 4051 K at current of 80 mA. The study suggests that SrZnSO:Bi3+ blue emitting phosphor has great potential in LED-based applications. Also inspires researchers to explore Bi3+-related phosphors with low energy excitation band and high absorption efficiency to develop high-quality n-UV pumped WLEDs.

A novel Eu-dependent G-La2Si2O7 single matrix phosphor for white light-emitting diodes

A novel G-La2Si2O7: Eu phosphor has been synthesized through SiC-reduction assisted with sol-gel method. Divalent Eu2+ and trivalent Eu3+ luminescent centers coexist in G-La2Si2O7: Eu lattice. Furthermore, two types of Eu2+ luminescent centers exist in G-La2Si2O7: Eu lattice, labeled as Eu1 and Eu2, arising from two La3+ crystallographic sites in G-La2Si2O7 host. Eu1 represents blue band emission while Eu2 shows green-yellow emission. Eu2+ selective occupation introduces Eu2+ large-scale blue-yellow regulation. Eu3+ shows typical red sharp line emission mainly located at 593 nm and 611 nm assigned to 5D0→7FJ (J = 1, 2) transitions. The luminescence process in G-La2Si2O7: Eu is discussed in details. Energy transfer processes from Eu3+ to Eu1 and Eu2, Eu1 to Eu2 occurs in G-La2Si2O7: Eu lattice. The influence of Eu dopant concentration is explored. As Eu increases, the dominant emission changes from Eu2+ to Eu3+. The coexistence of Eu1, Eu2 and Eu3+ brings G-La2Si2O7: Eu blue to red regulation. Fixing Eu doping at 0.5%, G-La1.99Si2O7: 0.01Eu sample shows a single-phased white light-emitting phosphor. At ultraviolet light 254 nm excitation, the emission spectrum approximate to full spectrum with a high rendering index of Ra = 91 is obtained using La1.99Si2O7: 0.01Eu sample at 254 nm excitation. Besides, G-La2Si2O7: Eu represents a good fluorescent thermal stability with luminous intensity keeping 80% (160 °C) of that at room temperature (30 °C), indicating G-La2Si2O7: Eu is a great potential single-matrix candidate in nUV-chip WLEDs.