Improved Luminescence Properties Research Articles

Effects of TMIn Flow Rate During Quantum Barrier Growth on Multi-quantum Well Material Properties and Device Performance in GaN-Based Laser Diodes

Abstract Multidimensional influence of indium composition in barrier layers on GaN-based blue laser diodes (LDs) are discussed through both material quality and device physics perspectives. LDs with higher indium content in the barriers demonstrate a notably lower threshold current and shorter lasing wavelength compared to those with lower indium content. Our experiments reveal that higher indium content in the barrier layers can partially reduce indium composition in the quantum wells, a novel discovery. Employing higher indium content barrier layers leads to improved luminescence properties of MQW region. Detailed analysis reveals that this improvement can be attributed to better homogeneity in the indium composition of the well layers along the epitaxy direction. InGaN barrier layers suppressed lattice mismatch between barrier and well layers, thus mitigating the indium content pulling effect in well layers. In supplement to experimental analysis, theoretical computations are performed, showing that InGaN barrier structures can effectively enhance carrier recombination efficiency and optical confinement of LD structure, thus improving output efficiency of GaN-based blue LDs. Combining these theoretical insights with our experimental data, we propose that higher indium content barriers effectively enhance carrier recombination efficiency and indium content homogeneity in quantum well layers, thereby improving the output performance of GaN-based blue LDs.

Improvement of luminescence properties in Zn2.1Mg0.9Ta2O8:Cr3+ by the cation substitution and its application in biological nondestructive testing and night vision lighting.

Recently, it is of great significance to explore near-infrared (NIR) phosphor with more application prospects. In this work, a series of Zn2.1 Mg(0.9 - y)GaySnyTa(2 - y)O8:0.003Cr3+ NIR broadband phosphors with high quantum yields and high thermal stability are discovered by uniquely replacing [Mg2+-Ta5+] in Zn2.1Mg0.9Ta2O8 with [Ga3+-Sn4+]. Under 460 nm excitation, Zn2.1Mg0.85Ga0.05Sn0.05Ta1.95O8: 0.003Cr3+ depicts the 600-1100 nm broadband emission with a full-width at half maximum (FWHM) of 210 nm, and the quantum yields can reach 61.2%. Finally, the phosphor was mixed with epoxy resin and encapsulated in a 460 nm blue light emitting diode (LED) chip to convert the NIR LED by phosphor (NIR pc-LED), which was applied in the field of biological nondestructive testing and night vision lighting.

Efficient and stable CsPbBr3/Cs4PbBr6 composite powders passivated and encapsulated with a novel silicon-based ligand

The metal halide perovskite have garnered significant attention for their exceptional photoelectric properties. However, their inherent instability and the sharp decrease of photoluminescence quantum yield (PLQY) in the solid-state significantly limit their practical applications. Appropriate heterojunction structures or matrix encapsulation can efficiently improve the PLQY and stability of the metal halide perovskite. Herein, we report a new silicon-based ligand hydrolysis condensation encapsulation to synthesize CsPbBr3/Cs4PbBr6/BTESPA-x (CPB–Si-x) composite powders with improved luminescence properties and enhanced thermal stability. With the increase of BTESPA (from 0 to 150 μL), the efficient hydrolysis condensation process occurs on the surface of CsPbBr3/Cs4PbBr6. Finally, the abundant amino-silane groups in BTESPA bind to undercoordinated Pb2+, thereby suppressing the surface defect states and enhancing the PLQY from 34.3 % for CsPbBr3/Cs4PbBr6 (CPB) to 82.1 % for CPB-Si-5. Simultaneously, the thermal stability of CPB-Si-5 exhibits a 13 % improvement over that of CPB after undergoing thermal cycling. Furthermore, tricolor white light-emitting-diode (WLEDs) with high color rendering index were fabricated using on-chip blue LED with bright green-emissive CPB-Si-5 composite powder and red-emissive K2SiF6:Mn4+ phosphor, demonstrating the potential applicability of these powders in WLED backlight systems.

Compound doping enables efficient CsPbBr3 nanocrystal light emitting diodes

All-inorganic cesium-based perovskite nanocrystals (PeNCs) attract much attentions in displays due to their facile synthesis protocol and superior luminous performance, while material instability hinders their practical applications. Herein, by inducing a multi-functional dopant, i.e., SrBr2, into the perovskite precursor solution, the as-formed SrBr2-doped CsPbBr3 NCs possess purer phases, suppressed defects and hydrophobic surfaces, which leads to a high photoluminescence quantum yield of ∼90 %, as well as much improved moisture stability. Benefiting from dopant passivation and improved luminescence properties, the doped CsPbBr3 light emitting diodes show five times and two times of current efficiency and external quantum efficiency improvements, respectively, in comparison to their undoped counterparts.

Synergistically improving luminescent properties of Eu2+, Dy3+ co-doped melilite with Bi3+ coupling

The improvement of luminescent properties is important for expanding the application of long afterglow phosphor (LAP). Here, the melilite-type Sr1·97MgSi2O7: Eu2+0.01, Dy3+0.02 LAP was studied with Bi3+ as the second co-dopant. Both photoluminescence (PL) and thermoluminescence (TL) were improved in terms of intensity and afterglow lifetime when the doping concentration of Bi3+ exceeded 2.5 mol%, and the optimized point was 3.5 mol%. As compared to the case of Eu2+ - Dy3+ double doping, the improved PL of Eu2+ - Dy3+ - Bi3+ triple doping samples was attributed to better photon absorption. The improved TL and afterglow were attributed to the synergistic strengthening density of the traps by Bi3+ and the deepening of trapping by Dy3+, if their distance was sufficient close. As a result, both TL and afterglow optimized at a concentration of 2 mol% Dy3+ - 3.5 mol% Bi3+ coupling.

Efficient white light emission from a single silicate host with promising color quality for white light emitting diodes

Strontium silicate phosphors were synthesized via a solid-state route with different silicon sources as SiO2 and Si3N4. The phosphors synthesized with Si3N4 exhibited improved luminescence properties for white emission because of the coexistence of Sr3MgSi2O8 and Sr2SiO4 phases. Under UV excitation, white light was observed due to the combination of blue emission from Sr3MgSi2O8: Eu2+ and yellow emission from Sr2SiO4: Eu2+. The broad Eu2+ emission was explained on the basis of the dependency of crystal field strength on the site selection. The variation of Eu2+ ion concentration controlled the quality of the emitted light and at 5 mol% Eu2+, near white emission (0.30, 0.31) was obtained with external and internal quantum efficiencies of 50% and 68%, respectively. The WLEDs were fabricated by coating the present phosphors on an InGaN UV- LED chips and the EL spectrum displayed near white chromaticity (0.31, 0.33) with color rendering index of 80 and CCT of 6850 K. The results demonstrated the promising single host phosphors for near-UV white-light-emitting diodes.

Layered Perovskite Doping with Eu3+ and β-diketonate Eu3+ Complex.

Metal halide perovskites are attracting great interest for the fabrication of light-emitting devices encompassing light-emitting diodes, lasers, and scintillators. As the field develops, perovskite doping emerges as a promising way to enrich the material functionalities and enhance the luminescence yield and tunability. While Mn+2 addition has been well explored, doping with lanthanides has received less attention, even though their intense and line-like luminescence is interesting for a wide range of applications. In this work, we study the doping of NMA2PbBr4 layered perovskites with Eu3+ and Eu3+ tetrakis β-diketonate complex. By exploiting the antenna effect of the naphthalene-based functional cation (NMA = 1-naphtylmethylammonium), direct sensitization of Eu3+ is obtained; nevertheless, it is not very efficient due to the non-optimal energy level alignment with the resonance acceptor level of the lanthanide. Protection of Eu3+ in the form of tetrakis β-diketonate complex grants a more ideal coordination geometry and energetic landscape for the energy transfer to europium in the perovskite matrix, allowing for a nearly 30-fold improvement in luminescence yield. This work sets the basis for new synthetic strategies for the design of functional perovskite/lanthanide host–guest systems with improved luminescence properties.

Sensitizing effect of Nd3+ on Tb3+ activated ZrP2O7 long persistent phosphor materials

The long persistent phosphors of Zr0.97P2O7:0.018Tb3+,0.012Nd3+ with Nd3+ as sensitized ions and Tb3+ as emission centers were synthesized using high temperature solid state reaction. The crystal structure and defects, excitation and emission spectra, decay curves and thermoluminescence (TL) curves of the phosphors were investigated. The synthesized Zr0.97P2O7:0.018Tb3+,0.012Nd3+ is essentially in line with the standard card PDF#49-1079. The emission band with main peak at 548 nm exhibits the characteristic transitions of 5D3-7Fj (j = 5, 4) and 5D3-7Fj (j = 6, 5, 4, 3) of Tb3+. The analysis of excitation and emission spectra shows that there exists the overlap between the emission peaks of Nd3+ at 466 and 485 nm and the excitation of Tb3+ at 443 and 485 nm, and the energy transfer from Nd3+ to Tb3+ plays an important role in the improvement of luminescence properties. The decay curves shows that Zr0.97P2O7:0.018Tb3+,0.012Nd3+ has longer afterglow time than ZrP2O7 and Zr0.982P2O7:0.018Tb3+. Additionally, the TL curves indicate that the trap depth at 0.72 eV in Zr0.97P2O7:0.018Tb3+,0.012Nd3+ is to the benefit of the afterglow time. The possible luminescence mechanism of ZrP2O7:Tb3+,Nd3+ is proposed on the basis of the XPS spectra, EPR spectra, excitation and emission spectra, decay curves, TL curves and the analysis of defect equations.

A novel DOTA-like building block with a picolinate arm for the synthesis of lanthanide complex-peptide conjugates with improved luminescence properties

Combination of complexes of lanthanide cations (Ln3+) for their luminescent properties and peptides for their recognition properties is interesting in view of designing responsive luminescent probes. The octadentate DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) chelate is the most popular chelate to design Ln3+ complex-peptide conjugates. We describe a novel building block, DO3Apic-tris(allyl)ester, which provides access to peptides with a conjugated nonadentate chelate, namely DO3Apic, featuring a picolinate arm in place of one of the acetate arms compared to DOTA, for improved luminescence properties. This building block, with allyl protecting groups, is readily obtained by solid phase synthesis. We show that it is superior to its analogue with tBu protecting groups for the preparation of peptide conjugates because of the difficult removal of the tBu protecting groups for the latter. Then, we compare two luminescent zinc fingers (LZF) comprising (i) a zinc finger peptide for selective Zn2+ binding, (ii) a Eu3+ complex and (iii) an acridone antenna (ACD) for long-wavelength sensitization of Eu3+ luminescence. The first one, LZF3ACD|Eu, incorporates a DOTA chelate for Eu3+ whereas the other, LZF4ACD|Eu, incorporates a DO3Apic chelate. Both act as Zn2+-responsive luminescent probes but we show that changing DOTA for DO3Apic results in a higher Eu3+ luminescence lifetime and in a doubling of the quantum yield, confirming the interest of the DO3Apic chelate and the DO3Apic(tris(allyl)ester building block for the preparation of Ln3+ complex-peptide conjugates. Additionally, the DO3Apic chelate provides self-calibration for LZF4ACD|Eu luminescence upon excitation of its picolinamide chromophore, making LZF4ACD|Eu a ratiometric sensor for Zn2+.

Uniform and Large‐Area Cesium‐Based Quasi‐2D Perovskite Light‐Emitting Diodes Using Hot‐Casting Method

AbstractMetal halide perovskites have deep valence band maximums (VBMs). For example, the VBM of CsPbBr3 is 5.8–6.3 eV. Conjugated polymers can be a potential candidate for the hole transport layer because of their deep highest occupied molecular orbital levels, but their poor compatibility with a hydrophilic perovskite precursor results in the formation of a noncontinuous perovskite film. In addition, antisolvent dripping methods for fabricating perovskite films cause spatially inhomogeneous nucleation, which is undesirable for large‐scale applications. In this work, efficient and large‐area perovskite light‐emitting diodes (PeLEDs) are developed by introducing a poly(9‐vinylcarbazole) (PVK) interlayer and employing a hot‐casting method (substrate preheating). The PVK interlayer increases the depth of the VBM of NiOx (from 5.1 to 5.5 eV), resulting in efficient hole injection. The thermal energy of the preheated substrate facilitates not only the growth of a continuous and pinhole‐free perovskite film, but also the formation of a highly crystalline and preferentially oriented perovskite structure, resulting in improved luminescence properties. Therefore, PeLEDs fabricated using an optimal preheating temperature show an improved external quantum efficiency (from 3.08% to 8.44%) with spatially uniform electroluminescence. Finally, the development of uniform and large‐area PeLEDs (with an active area of 12.8 cm2) is demonstrated.

Improved luminescence properties of a novel red dodec-fluoride phosphor Ba3Sc2F12:Mn4+ with extraordinary thermal stability for WLED application

A red phosphor, Ba3Sc2F12:Mn4+, with extraordinary thermal stability and for application in “warm” white LEDs for backlighting, was obtained at room temperature and its luminescence intensity has been improved by optimizing its synthetic parameters.

Mechanism of Improved Luminescence Intensity of Ultraviolet Light Emitting Diodes (UV-LEDs) Under Thermal and Chemical Treatments

In this work, the influences of thermal annealing and chemical passivation on the optical and electrical properties of ultraviolet light-emitting-diode (UV-LED) were investigated. The electroluminescence (EL) intensities of the LEDs under KOH treatment and thermal annealing increased by 48% and 81%, respectively compared to as-fabricated LED under current level of 10 mA. Cathodoluminescence (CL) mapping of UV-LEDs confirmed no variation of the density of the non-radiative recombination centers after surface treatments, and no obvious change in surface morphology was identified due to lacking of energy for surface atom migration. However, Raman spectroscopy indicates a relaxation of compressive strains inside the thin film after both thermal and chemical treatments, and conductive atomic force microscopy (c-AFM) also illustrated reduced leakage current after KOH passivation, which are responsible for the improved luminescence properties of UV-LEDs.

Facile synthesis, vibrational, optical and improved luminescence properties analysis of Ca2KZn2V3O12 phosphor

A self-activated Ca2KZn2V3O12 (CKZVO) phosphor was synthesized by the solid state reaction method under different calcination temperatures. A high crystalline single-phased CKZVO material occurred at 600 °C belongs to the cubic structure with Iad space group. The vibrational modes were characterized by IR and Raman spectra. All the samples consist of intense absorption spectra in UV region owing to charge transfer of (VO4)3− tetrahedral group and the band gap energy of the single-phased CKZVO phosphor was found to be 3.2 eV. Photoluminescence broad emission spectrum ranging from 400 to 700 nm, ascribing to the charge transfer in (VO4)3− tetrahedral group. The colorific properties of the single-phased CKZVO phosphor was investigated and reported. Ultimately, the device performance showed that the self-activated Ca2KZn2V3O12 phosphor served as a potentially applicable candidate in UV chip excited white LED applications.

Improved luminescence properties of Na2TiSiO5 phosphor by the Ge4+ doping in the crystal lattice

Improved luminescence properties of Na2TiSiO5 phosphor by the Ge4+ doping in the crystal lattice

Influence of cerium content and heat treatment on Ce:YAG@glass wool nanostructures

The paper reports the influence of cerium content and heat treatment on composition, structural features and optical properties of nanostructures constituted by a layer of Ce:YAG nanoparticles on glass wool (Ce:YAG@GW). The Ce:YAG@GW nanostructures were obtained embedding the glass wool (GW) in a gel-like precursor and calcining at 800 and 900 °C. Gel-like precursor of urea glass route (UGR) method has been used to prepare both nanostructures and Ce:YAG nanoparticles prepared as references. Structural properties were investigated by using X-ray diffraction (XRD) and infrared spectroscopy (IR). Results showed that the composition of the final products strongly depends both on the cerium content and temperature. Optical properties of best materials have been investigated in order to verify their suitability for lighting applications. Obtained results show relatively high quantum efficiency for Ce:YAG@GW treated at 800 °C comparing with the Ce:YAG nanoparticles obtained at the same temperature confirming the improved luminescence properties of the nanoparticles when they are applied on GW surface.

Enhanced up-conversion luminescent properties of KYb2F7:Er3+ by Sc3+ doping

In the field of up-conversion materials, Yb3+ is usually used as sensitizer. In this work, KYb2F7 is synthesized by hydrothermal method using Yb3+ as a part of the matrix material, and at the same time, the luminescent center Er3+ and the non-luminescent center Sc3+ are co-doped therein. It was found that Yb3+ can be introduced into the matrix material with improved luminescence properties. In addition, with the doping of Sc3+, the luminescence intensity of the material can be increased by up to five times. This testified that the doping of an appropriate amount of non-luminescent center Sc3+ can significantly improve the up-conversion luminescence intensity of up-conversion material.

Improved luminescence properties by the self-assembly of lanthanide compounds with a 1-D chain structure for the sensing of CH3COOH and toxic HS− anions

A family of lanthanide compounds has been explored and enhanced luminescence has been accomplished by doping method. A brand new and multifunctional fluorescence probe was developed, which was able to detect CH3COOH and HS− with different mechanisms.

Effect of alkali metal ions on the spectra of CaZn2(PO4)2: Sm3+ phosphor analyzed by J-O theory

To investigate the effect of alkali metal ions on the spectra of CaZn2(PO4)2: Sm3+ phosphor. Here, we prepared a series of doped and undoped CaZn2(PO4)2 were prepared by the high temperature solid-state reaction method. The microstructure and luminescence properties were systematically investigated by the experimental and theoretical methods. Rietveld refinement of XRD data was performed to indicate the crystal parameters variation, caused by introducing rare earth ions (Sm3+) and charge compensation ions (Li+, Na+, K+). To further understand the role of doped ions, we applied density functional theory to calculate the band structure and density of states of CaZn2(PO4)2. The excitation and emission spectra showed the intense excitation peak at 402 nm and emission peak at 598 nm. The intensities of those spectra were enhanced after adding the charge compensation ions. The Judd-Ofelt theory based on the absorption spectra was applied to predict the transition probability, branching ratio and quantum efficiency, and to explain the improved luminescence properties. The mechanism of concentration quenching was investigated by the optical luminescence system of CaxZn2-x(PO4)2: xSm3+, xLi+. The results showed that the dipole-dipole interaction dominated in non-radiative energy transfer when the concentrantion of Sm3+ ions was higher than the quenching concentration 3 mol%. This work has the potential application in n-UV excited LED and other orange-red luminescent devices.

Improved luminescence properties of MoS2 monolayers grown via MOCVD: role of pre-treatment and growth parameters

Fabrication of transition metal dichalcogenides (TMDCs) via metalorganic chemical vapor deposition (MOCVD) represents one of the most attractive routes to large-scale 2D material layers. Although good homogeneity and electrical conductance have been reported recently, the relation between growth parameters and photoluminescence (PL) intensity—one of the most important parameters for optoelectronic applications—has not yet been discussed for MOCVD TMDCs. In this work, MoS2 is grown via MOCVD on sapphire (0001) substrates using molybdenum hexacarbonyl (Mo(CO)6, MCO) and di-tert-butyl sulphide as precursor materials. A prebake step under H2 atmosphere combined with a reduced MCO precursor flow increases the crystal grain size by one order of magnitude and strongly enhances PL intensity with a clear correlation to the grain size. A decrease of the linewidth of both Raman resonances and PL spectra down to full width at half maxima of 3.2 cm−1 for the E2g Raman mode and 60 meV for the overall PL spectrum indicate a reduced defect density at optimized growth conditions.

Development of oxyfluoroborate glass ceramics doped with Er3+ and Yb3+

The preparation of oxyfluoroborate glasses and glass–ceramics doped with Yb3+ and Er3+ with improved luminescent properties is reported. Glasses with compositions (100 − x − y) (MO·2B2O3) + xPbF2 + y(YbF3:ErF3) (% in mol), where M is Sr, Ba, Ca, x = 10–40% and y = 0, 1 or 5% were prepared by the melt/quenching technique. Glass crystallization was studied using thermal analysis and X-ray diffraction techniques. Optical absorption and infrared up-conversion were studied on both glasses and glass–ceramics. The incorporation of a fluoride compound into the borate glass resulted to depend on the ionic radius of the glass modifier: as it increases, glasses become more stable against crystallization. On the other hand, alkali–fluoride compounds such as BaF2 and SrF2 can be crystallized from these systems by selecting an appropriate proportion between their components. Furthermore, the up-conversion response can be tuned by changing the glass modifiers (Sr, Ba and Ca) of the borate matrix, which also influence the type of fluoride crystallized compound. The strontium glass–ceramics have the highest luminescence response due to the crystallization of SrF2 compound in the system SrO–B2O3–PbF2. Meanwhile, the lowest luminescence signal was obtained for samples in the system BaO–B2O3–PbF2 where the Pb1.33Ba2.66B11FO20 phase crystallizes. With this strategy, new materials with improved luminescence properties that can be used as up converters, were obtained.