UV LED Chip Research Articles

Facile Synthesis of Highly Emissive All-Inorganic Manganese Bromide Compounds with Perovskite-Related Structures for White LEDs

Lead-free all-inorganic halide materials with different Mn2+-based crystal structures (Cs3MnBr5 and CsMnBr3) were obtained using a convenient synthetic method. Cs3MnBr5 had a bright green emission (522 nm), with a unique single-exponential lifetime (τavg = 236 µs) and a high photoluminescence quantum yield (82 ± 5%). A red emission was observed in the case of the CsMnBr3 structure with a two-exponential fluorescence decay curve, and the lifetime was 1.418 µs (93%) and 18.328 µs (7%), respectively. By a judicious tuning of the synthetic conditions, a mixed phase of Cs3MnBr5/CsMnBr3 was also produced that emitted white light, covering almost the entire visible spectrum. White-light-emitting diodes (WLEDs) with color coordinates (0.4269, 0.4955), a color temperature of (3773 K), and a color rendering index (68) were then fabricated using the as-prepared powder of mixed phases of Cs3MnBr5/CsMnBr3 with a commercial UV LED chip (365 nm).

Zero-thermal-quenching of LiAl5O8: Eu2+, Mn2+ phosphors by energy transfer and defects engineering

The photoluminescence behavior of inorganic phosphors is generally influenced by thermal stability, which determines the luminescence efficiency of the corresponding devices. Here, a series of Eu2+, Mn2+ co-doped LiAl5O8 blue-green-emitting phosphors with thermal robust are successfully fabricated. The concentration-dependent emission spectra and the decay curves of the as-obtained LiAl5O8: Eu2+, Mn2+ samples manifest the occurrence of the energy transfer from Eu2+ to Mn2+ ions via dipole-dipole interaction, and the corresponding emitted colors are gradually modulated from blue to green under the excitation of 310 nm. Moreover, the zero-thermal-quenching luminescence is observed when the operation temperature is up to 423 K, which is attributed to the energy release from the trapping centers to emitting centers (Eu2+ and Mn2+) at high temperature. Furthermore, a warm white light-emitting diodes (WLEDs) device with correlated color temperature of 5061 K, a color rendering index of 80.6 and long-term stability is fabricated by combining UV LED chip (λex = 310 nm), as-obtained LiAl5O8: Eu2+, Mn2+ phosphor, commercially available red phosphor and green phosphor. These results prove the potential application of the as-obtained LiAl5O8: Eu2+, Mn2+ phosphor for UV-pumped WLEDs devices.

Considerable improved near-infrared luminescence in ionic-free doped ZnAl2O4 by oxygen defects engineering

Recently, the phosphor for near-infrared LED is of importance, and a lot of the researches have been attracted on the synthesis and composition design. However, the large number of researches for near-infrared luminescent materials mainly focus on activator ions doped inorganic materials, including rare earth ions and transition metal ions. Here, an ionic-free doped NIR phosphor of ZnAl2O4 is proposed for NIR LED through oxygen defects engineering. The spinel-structured ZnAl2O4 phosphors with deficiency of zinc were synthesized by high temperature solid state reaction, which were characterized by a series of techniques, including XRD, UV–Vis, XPS, EPR, DFT calculation, PLE/PL spectroscopy, and temperature-dependent PL spectra analysis. The deficiency of zinc results in the appearance of zinc vacancy (VZn) and oxygen vacancy (VO). Most of the oxygen vacancy is VO+, along with a small content of VO++ in ZnAl2O4. Under the excitation of ultraviolet light at 302 nm, the phosphor outputs a broad near-infrared emission band with the maximum at 715 nm. Higher concentration of zinc deficiency leads to stronger near-infrared luminescence, because of the increased oxygen vacancy. The phosphors exhibited a good thermal stability, and they were successfully packaged on the 285-nm UV LED chip, which outputted bright and intense near-infrared light, indicating that the NIR phosphors synthesized in this work have the prospect application in NIR LED.

Fabrication of W-LEDs by Coating Tri-Color Inorganic Phosphors on UV-Diode

YAG:Ce phosphor coated on blue-chip gives many advantages, except the color rendering of the LEDs fabricated by this method is poor due to the lack of red and green colors. This problem can be sorted out by choosing different methods out of the available two different methods. For the first method, the n-UV (near-ultraviolet) LED is coated with a mixture of intense blue, green, and red phosphors to make a white light-emitting diode. Also, if the yellow color phosphor is added, lamps can give better CRI values. So many papers are reported on this type of white LED fabrication technique. In this paper, we have reported the fabrication of white LED lamps by coating three different phosphors i.e. blue, green, and red in the appropriate amount to be mixed and coated on the near UV LED chips. This approach is different from the existing reports because we are using near UV (405-407 nm LEDs) not the UV LED chips in the fabrication of white LEDs in this paper.

Anti-solvent polarity engineering for structure, morphology and composition control of cesium copper (I) halide with efficient, stable and adjustable photoluminescence

In this work, cesium copper (I) halide micro-crystals (MCs) were demonstrated to experience structure, morphology and composition evolutions by tuning the polarity of the anti-solvent. It was fond that, when anti-solvents with the polarity higher than 4.3+ were used, rod-like phase-pure CsCu2I3 MCs, rather than Cs3Cu2I5 MCs, preferred to be formed. However, when the anti-solvents with polarity came to lower than 4.3-, particle-state Cs3Cu2I5 MCs would be produced. With the structural evolution from CsCu2I3 to Cs3Cu2I5, the photoluminescence emission changed from yellow to blue, with high photoluminescence quantum yields (PLQYs) of 15.3% and 89.5%, respectively. Amazingly, by a fine tuning of the polarity in the range from 4.3+ to 4.3-, the mixing ratio of CsCu2I3 and Cs3Cu2I5 MCs can be adjusted directly, with tunable Commission Internationale de L′Eclairage (CIE) color coordinates from cold white to white and warm white, by changing the relative volume of the anti-solvent. Note that, the dependences of the production on the polarity of the anti-solvent showed rather wide precursor’s molar ratio and concentration processing windows. At last, the as-prepared white-light mixture was placed onto a UV LED chip to fabricate a white-light emitting diode (WLED). The device showed a high color rendering index of 87.3, a CIE color coordinate of (0.32, 0.33), and a long life time of more than 100 h. The discovered relationships between the anti-solvent polarity and structural evolution of the cesium copper (I) halide MCs enriched our understanding about copper-containing perovskite-like halides. The method to fabricated white-light phosphor in one step greatly simplified the technological process and reduced the production cost. And, the perfect stability of the WLED demonstrated promising application prospect of CsCu2I3 and Cs3Cu2I5 MCs in next-generation solid-state lighting.

Self-Activating Strontium Orthoborate Blue Phosphors Induced by Cation and Anion Deficiencies and Their Rare-Earth-Free White Ultraviolet Light-Emitting Diodes.

Self-activating blue-light-emitting strontium orthoborate phosphors, viz., Sr3B2+xO6+3x/2 and Sr3B2+xO6+3x/2-δ (x ranges from -0.3 to 0.1), were obtained by varying the number of BO3/2 and anion deficiencies. The integrated intensity observed from the oxygen 1s profile obtained via X-ray photoelectron spectroscopy indicated the relative concentrations of the oxygen vacancies in the Sr3B2+xO6+3x/2 (x = 0, -0.1, and -0.3) and Sr3B2O6-δ phosphors. The structures of Sr3B2O6, Sr3B2.1O6.15, Sr3B1.9O5.85, and Sr3B2O6-δ with crystal orientations were analyzed based on high-resolution synchrotron powder X-ray diffraction data. A mixture of rare-earth-free blue Sr3B2O6-δ and yellow Sr2.45Ba0.5Na0.05Al0.95Sn0.05O4-αF1-δ phosphors, incorporated on a 315 nm UV-LED chip, can generate a white-light UV-LED.

In situ synthesis of MAPbX3 perovskite quantum dot-polycaprolactone composites for fluorescent 3D printing filament

The development of functionalized polymer-based filament enables the fused deposition modeling (FDM) 3D-printed materials or structures with a wide range of unique functions. This work explores the use of MAPbX3 (MA = CH3NH3, X = Cl, Br, I or mixture of them) perovskite quantum dots (PQDs) by harnessing their unique optical properties for the development of fluorescent 3D printing filaments. Firstly, a one-pot strategy for scalable synthesis of MAPbX3 PQDs-polycaprolactone (PCL) composite was proposed by in situ formation of PQDs in PCL matrix. To demonstrate the ability for the obtained PQDs-PCL composites to fabricate fluorescent filaments, the effects of filament functionalization on optical properties of PQDs, as well as thermal and mechanical properties of polymer matrix were then comprehensively studied. Owing to the good protective capability of PCL, the synthesized PQDs-PCL composites exhibit comparable PLQY and enhanced UV, water and thermal stability compared to that of pure PQDs. Moreover, high concentration of embedded PQDs in PQDs-PCL composites was obtained with decreasing amount of PCL. The aggregation of PQDs at high temperature combined with the poor interaction between PQDs and surrounding PCL matrix led to the decreased thermal transition temperature and reduced mechanical properties in PQDs-PCL composites relative to pure PCL. The glass transition temperature was found to decrease by 5.5 °C, while the mode of failure changed from plastic fracture for pure PCL to brittle fracture for the highest concentration of PQDs in PCL tested. Consequently, PQD-PCL composites were further processed into fluorescent filaments and further fluorescent objects or structures via 3D printing. Green LED and white LED devices were realized by the combination of UV LED chip with 3D printed MAPbBr3 PQD-PCL thin-film, and blue LED chip with MAPbBr3 PQD-PCL thin-film and K2SiF6:Mn4+ phosphor, respectively, demonstrating that the PQDs-functionalized 3D printing filaments have great potential in fields of optoelectronic application.

Sterically Stabilized Carbon Dots as Solid-State Phosphors for White-Light-Emitting Diodes

Solid-state photoluminescence (PL) is highly important for practical optoelectronic applications. However, conventional carbon dots often suffer from fluorescence quenching induced by aggregation in a solid state, limiting their potential applications. In this report, sterically stabilized polymeric carbon dots (PCDs) (<2 nm) are prepared to achieve effective PL emission even in the solid-sate composite using a simple one-step hydrothermal treatment. These PCDs show unique fluorescence properties of tunable PL color change with the concentration covering the visible spectrum range from blue to orange in aqueous solution and the wavelength-dependent broad PL with maximum excitation at around 480 nm in solid-state epoxy composite. Practically applicable “single phosphor on a chip” in white-light-emitting diodes (WLEDs) application is successfully demonstrated by combining our PCDs/epoxy composite with a 460 nm blue-based LED chip, which is longer than most studies on the performance of CD-related white LEDs using UV or deep-blue LED chips as the excitation source. These results suggest that this type of PCDs may not only effectively suppress the aggregation-caused quenching effect in solid matrices but also show enhanced PL properties as a solid-state phosphor for practical white light emission applications.

Nonstoichiometric LaO0.65F1.7 Structure and Its Green Luminescence Property Doped with Bi3+ and Tb3+ Ions for Applying White UV LEDs.

Red–green–blue phosphors excited by ultraviolet (UV) radiation for white light LEDs have received much attention to improve the efficiency, color rendering index (CRI), and chromatic stability. The spectral conversion of a rare-earth ion-doped nonstoichiometric LaO0.65F1.7 host was explored with structural analysis in this report. The nonstoichiometric structure of a LaO0.65F1.7 compound, synthesized by a solid-state reaction using La2O3 and excess NH4F precursors, was analyzed by synchrotron X-ray powder diffraction. The crystallized LaO0.65F1.7 host, which had a tetragonal space group of P4/nmm, contained 9- and 10-coordinated La3+ sites. Optical materials composed of La1−p−qBipTbqO0.65F1.7 (p = 0 and 0.01; q = 0–0.2) were prepared at 1050 °C for 2 h, and the single phase of the obtained phosphors was indexed by X-ray diffraction analysis. The photoluminescence spectra of the energy transfer from Bi3+ to Tb3+ were obtained upon excitation at 286 nm in the nonstoichiometric host lattice. The desired Commission Internationale de l’Eclairage (CIE) values of the phosphors were calculated. The intense green La0.89Bi0.01Tb0.1O0.65F1.7 phosphor with blue and red optical materials was fabricated on a 275 nm UV-LED chip, resulting in white light, and the internal quantum efficiency, CRI, correlated color temperature, and CIE of the pc LED were characterized.

Multifunctional Fluorescent Copper Nanoclusters for Ag+ Sensing, Anticounterfeiting, and Blue/White Light-Emitting Diodes

Copper nanoclusters (CuNCs) with bright blue-emitting fluorescence have been synthesized via a simple one-pot process using 2-mercapto-1-methylimidazole (MMI) as a stabilizer. The as-prepared MMI-CuNCs exhibited a high quantum yield of 19.2%, a long luminescence lifetime of 10.57 μs, and excellent photostability. Significantly, the fluorescence intensities of MMI-CuNCs were effectively quenched with addition of Ag+ ions, and the MMI-stabilized CuNCs were developed as a sensitive fluorescent nanoprobe for the label-free determination of silver ions for the first time. The fluorescence sensor provided a fast linear response toward Ag+ in the range of 0.025–50 μM, with a detection limit of 6.7 nM. The fluorescence quenching mechanism was ascribed to an agglomeration-induced effect and static quenching. A fluorescence sensing platform was successfully applied for Ag+ detection in human serum samples with good accuracy and high reproducibility, signifying the practical applicability of the assay. Additionally, MMI-CuNCs displayed good solid-state blue emission and are suitable for security ink applications. The MMI-CuNCs were utilized as a color conversion layer to construct blue- and white-light-emitting diodes (LEDs) with excellent white light properties by a facile combination of MMI-CuNCs and UV LED chips. This result facilitates multiple functions of MMI-CuNCs in the application of label-free sensors, anticounterfeiting, and optical devices.

Compact ultrabroadband light-emitting diodes based on lanthanide-doped lead-free double perovskites

Impurity doping is an effective approach to tuning the optoelectronic performance of host materials by imparting extrinsic electronic channels. Herein, a family of lanthanide (Ln3+) ions was successfully incorporated into a Bi:Cs2AgInCl6 lead-free double-perovskite (DP) semiconductor, expanding the spectral range from visible (Vis) to near-infrared (NIR) and improving the photoluminescence quantum yield (PLQY). After multidoping with Nd, Yb, Er and Tm, Bi/Ln:Cs2AgInCl6 yielded an ultrabroadband continuous emission spectrum with a full width at half-maximum of ~365 nm originating from intrinsic self-trapped exciton recombination and abundant 4f–4f transitions of the Ln3+ dopants. Steady-state and transient-state spectra were used to ascertain the energy transfer and emissive processes. To avoid adverse energy interactions between the various Ln3+ ions in a single DP host, a heterogeneous architecture was designed to spatially confine different Ln3+ dopants via a “DP-in-glass composite” (DiG) structure. This bottom-up strategy endowed the prepared Ln3+-doped DIG with a high PLQY of 40% (nearly three times as high as that of the multidoped DP) and superior long-term stability. Finally, a compact Vis–NIR ultrabroadband (400~2000 nm) light source was easily fabricated by coupling the DiG with a commercial UV LED chip, and this light source has promising applications in nondestructive spectroscopic analyses and multifunctional lighting.

Recent Advances in Packaging Technologies of AlGaN‐Based Deep Ultraviolet Light‐Emitting Diodes

AbstractAlGaN‐based deep ultraviolet light‐emitting diodes (UV LEDs) have gained rapidly growing attention due to their wide applications in water purification, air disinfection, and sensing as well as optical communication. Moreover, deep UV radiation has been verified as one of effective way to inactivate COVID‐19. However, although numerous efforts have been made in deep UV LED chips, the reported highest external quantum efficiency (EQE) of them is 20.3%, which is far lower than that of visible LEDs. The EQE of commercial packaged AlGaN‐based deep UV LEDs is usually lower than 5%, which will cause serious reliability problems as well. Therefore, it is very urgent to improve EQE and reliability of the devices from packaging level. In this review, a systematical summarization about the packaging technologies of AlGaN‐based deep UV LEDs has been analyzed and future prospects have been made as well. Firstly, this work provides a brief overview of the devices and analyzes why the packaging level reduces EQE and reliability in theory. Then, systematically reviews the recent advances in packaging technologies and deep UV micro‐LEDs. Finally, conclusions and outlooks are given as well. This review is of great significance for promoting the development of the packaging technologies for AlGaN‐based deep UV LEDs.

Te4+/Bi3+ Co-Doped Double Perovskites with Tunable Dual-Emission for Contactless Light Sensor, Encrypted Information Transmission and White Light Emitting Diodes

• The energy transfer between Bi 3+ and Te 4+ is realized in Cs 2 ZrCl 6 perovskite. • Bi 3+ /Te 4+ co-doped perovskite can realize color hue evolution from blue to yellow. • High quality WLEDs can be fabricated by Cs 2 ZrCl 6 : Bi 3+ , Te 4+ and UV LED chip. • The phosphor can be exploited in visual light sensor and information transmission. Stable and high-efficiency inorganic lead-free double perovskites have aroused great attention for their application in photoluminescence field. However, most of the double perovskite materials with single dopant cannot realize multi-mode excitation, tunable or full-spectrum emission, which lead to the rare applications in contactless light sensor, encrypted information transmission and white light emitting diodes. Herein, inspired by a traditional methodology of co-doping rare-earth, ns 2 type ions (Bi 3+ and Te 4+ ) co-doped lead-free perovskite Cs 2 ZrCl 6 is proposed and developed. Comparing to the single dopant, Bi 3+ /Te 4+ co-doped perovskites can exhibit high sensitivity to the excitation wavelength and then emit greatly adjustable emission spectra from ∼457 to 577 nm, which corresponds to the color hue evolution from blue to yellow. Meanwhile, the high resonance energy transfer efficiency process from triplet STEs state of Bi 3+ to Te 4+ is also proved by employing the excitation/emission spectra and the transient fluorescence spectrum. Based on the efficient energy transfer process, high quality white light (CIE = (0.330, 0.347), CCT = 5608 K, Ra = 85.1), covering the entire visible region, can be obtained under ultraviolet light excitation. These features guarantee its potential application in contactless light sensor, encrypted information transmission and single-phase white light emitting diodes. The above results show that the methodology of co-doping ns 2 type ions in Cs 2 ZrCl 6 will open up new opportunities to the multifunctional application field.

Characterization of structural and optical properties of Mn2+ -doped Zn2 GeO4 nanorods as an efficient green phosphor for solid-state lighting.

A series of Mn2+ -doped zinc germinate ZGO:xMn2+ (x = 0-0.05) nanorods was synthesized successfully using a hydrothermal method. XRD revealed that crystal phases of the ZGO:xMn2+ were rhombohedral and in the R-3 space group. The Williamson-Hall equation was also used to explain the strain, nanocrystalline size, and stacking fault. Green LEDs were successfully fabricated by coating ZGO:Mn2+ nanorods onto UV-LED chips. For high color purity, CIE of the fabricated green LEDs were (0.2404, 0.5428), which made this material a promising candidate for fabrication of UV-based green LEDs.

Bifunctional samarium activated red-emitting and thermal resistant phosphor for simultaneous field emission displays and white light-emitting diodes

A series of Sm 3+ -activated Ca 3 Gd(AlO) 3 (BO 3 ) 4 red-emitting phosphors were prepared by a traditional high-temperature solid-state approach. They were characterized by XRD refinements, TEM, SEM, EDS, DRS, FTIR, Raman spectra, photoluminescence (PL) spectra, and fluorescence decay curves. The microstructure of the cation-borate phosphors and the presence of Sm 3+ dopants, and their impact at the Ca and Gd sites were studied. All the samples exhibited bright red emissions caused by intra-4f transitions of Sm 3+ ions when excited at 404 nm. The optimum dopant concentration was 4mol%, and the concentration quenching (CQ) process was driven by dipole-dipole interaction using Inokuti-Hirayama, and Dexter theories. Interestingly, the temperature-dependent PL spectra manifested that the resulting phosphor had excellent thermal stability with an activation energy of 0.234 eV. Ultimately, the investigated phosphor demonstrated excellent chemical stability. The Sm 3+ -doped CGAB:Sm 3+ phosphor can convert NUV LED chips into intense red emission with Commission Internationale de l’Eclairage (CIE) diagrams of 0.615, 0.382 and high color purity of up to 95.6%. The WLED containing CG 0.96 AB:0.04Sm 3+ merged with the commercial phosphors revealed low correlated color temperature (CCT≈4197 K) and high color rendering index (CRI≈89.7). EL spectrum of the fabricated Red-LED device. Inset exemplifies the coordination diagram and image for the red phosphor. UV excitation induced bright red emissions with high color purity and outstanding thermal-quenching (TQ) resistance. Luminescent pictures of the prepared Red–LED and White-LEDs device with the input current. • UV excitation induced bright red emissions with high color purity up to 95.6%. • They possessed good chemical stability in an existing environment. • The CG 0.96 AB:0.04Sm 3+ exhibited outstanding thermal-quenching (TQ) resistance of>90.8%. • Red LED and WLED devices were fabricated by using phosphor and UV LED chips.

Achievement of high-efficiency sunlight-like emission in Rb2CaP2O7: Ce3+, Eu2+ phosphors

High quantum efficiency and thermal stability have always been the goals to pursue and challenges for lighting application. In this work, sunlight-like white emission has been achieved in a new prepared single phased Rb2CaP2O7: 0.005Ce3+, 0.01Eu2+ phosphor, which exhibits high internal quantum efficiency (IQE = 74.36%), external (EQE = 56.77%) quantum efficiency and excellent thermal stability. Based on the broadband emission from 4f-5d transitions of Ce3+/Eu2+ ions and high energy transfer efficiency of Ce3+→Eu2+ (measured up to 60%), the extremely wide color-tunable emission from blue-violet to white and then to orange-yellow is realized in Rb2CaP2O7: 0.005Ce3+, xEu2+ phosphors. Moreover, a prototype WLED device is packaged by combing the prepared Ra2CaP2O7: 0.005Ce3+, 0.01Eu2+ white phosphors with an UV LED chip (λ = 310 nm), and the obtained WLED emits bright sunlight-like white light with color coordinates of (0.377, 0.324). The correlated color temperature (CCT) and the color rendering index (CRI) value of the WLED are 3208 K and 88.4, respectively. These results can provide effective guidance for the design of color-tunable single-phase white phosphors with high luminous efficacy and thermal stability.

Photoluminescent Properties of Red-emitting AlPO4:Cr3+ Phosphor for Plant Growth LEDs

In this study, red-emitting AlPO4:Cr3+ phosphors have been successfully synthesized by a facile sol-gel method. The Tanabe–Sugano diagram demonstrates that the surrounding sites of Cr3+ ions has a high crystal field with Dq/B=2.47. The sharp 694-nm peak on the PL of AlPO4:Cr3+ phosphor could be attributed to the 2E→4A2 electron transition of Cr3+ ions. The AlPO4:0.3%Cr3+ phosphor presents the highest PL intensity, then a purple LED prototype is obtained by coating the optimum powder on a UV LED chip. The color coordinates (0.2412, 0.1330) of the purple LED prototype implies that AlPO4:Cr3+ phosphors are promosing to be used as deep red phosphor powder for horticulture LED lighting.

Emission-tunable Ba2Y1–xScxNbO6:Bi3+ (0 ≤ x ≤ 1.0) phosphors for white LEDs

Here, we report a series of Bi3+-doped Ba2Y1–xScxNbO6 (0 ≤ x ≤ 1.0 mol) phosphors by using the traditional high temperature solid-state reaction. To achieve the structural and photoluminescent (PL) information, several experimental characterizations and theoretical calculations were carried out, including X-ray diffraction (XRD), Rietveld refinement, UV-visible diffuse reflectance and PL spectra, temperature dependent PL spectra, and density functional theoretical (DFT) calculations. The XRD results show that the Bi3+-doped Ba2Y1–xScxNbO6 samples belong to the double-perovskite phase with a cubic space group of Fm3̅m, and the diffraction positions shift toward high diffraction angle when the larger Y3+ ions are gradually replaced by the smaller Sc3+ ions. In addition, the refined XRD findings show that the Bi3+ ions tend to substitute the Y3+ and Sc3+ sites in the Bi3+-doped Ba2Y1–xScxNbO6 (0 <x < 1.0 mol) solid solutions. The PL spectra show that the emission positions of the solid solution samples tune from 446 to 497 nm with the increase of Sc3+ content, which can be attributed to the modification of crystal field strength around Bi3+ ions. Moreover, there is energy transfer from the Ba2YNbO6 host to Bi3+ ions, which is dominated by a resonant type via a dipole-quadrupole (d-q) interaction. The Ba2Y0.6Sc0.4NbO6:0.02 molBi3+ shows the strongest PL intensity under 365 nm excitation, with the best quantum efficiency (QE) of 68%, and it keeps 60% of the room temperature emission intensity when the temperature increases to 150 °C, meaning that the Ba2Y0.6Sc0.4NbO6:Bi3+ features excellent thermal quenching of luminescence. By combining this optimal sample with a commercial red-emitting Sr2Si5N8:Eu2+ phosphor, and a commercial 365 nm UV LED chip, a white LED device, with the color temperature (CT) of 3678 K, color rendering index (CRI) of 67.9, and CIE coordinates at (0.371, 0.376), is achieved.

Dye encapsulation engineering in a tetraphenylethylene-based MOF for tunable white-light emission

The development of efficient and stable white-light emissive materials is highly desirable in displays and solid-state lighting. Here we present a high-quality white-light emitter based a dual-emitting MOF hybrid, which is achieved by dye encapsulation engineering within a robust Zr-MOF (PCN-128W) containing a highly luminescent tetraphenylethylene-based ligand. The pore confinement effect well isolates the incorporated dye molecules (trans-4-[4-(Dimethylamino)styryl]-1-methylpyridinium iodide (DSM)) and therefore suppress the aggregation caused luminescence quenching. The dye emission is mainly sensitized by PCN-128W host through Förster resonance energy transfer (FRET), and the FRET process is incomplete, thus enabling the hybrid to feature dual emissions upon a single excitation. The emission color of DSM@PCN-128W hybrid can be systematically tuned from blue to white, and to orange by regulating the dye encapsulation content. A broad white-light emission with a considerably high quantum yield (21.2%) is obtained in the case of dye contents of 0.15 wt%. The luminescence of DSM@PCN-128W hybrid is stable in ambient air for over 1 month, and show good resistance to continuous UV light irradiation, owing to the protective MOF Matrix that largely inhibits the UV exposure to dye molecules. What’s more, by combining DSM@PCN-128W with a commercial UV LED chip, we fabricate a white-light emitting prototype device showing CIE chromaticity coordinates of (0.34, 0.33), a CRI of 79.1, and a CCT of 5525 K.

A spectroscopic experimental and semi-empirical study of [Eu(salen)2] as a red-emitter for phosphor-converted UV LED

Most of commercial WLEDs have a lack of red-emission component resulting in cool white illumination. Aiming this issue, in this paper, we present the synthesis of [Eu(salen)2] with a Schiff base type ligand, the salen (N,N′-ethylene-bis(salicylidenimine)), another lanthanide complex was also investigated, the [Gd(salen)2]. Both complexes were characterized by conventional spectroscopy techniques to confirm their preparation, and the free software LUMPAC was used as a friendly interface to determine the experimental intensity parameters (Ω2 and Ω4) for the Eu-complex, it was also used to optimize the complex structure, perform theoretical calculations of excited states, and intensity parameters. The Eu-complex was immobilized in PMMA films in different amounts, and their photophysics properties were analyzed. The 7.5 wt% doped film showed the best photophisical results (τ = 0.226 ms; ΦEuEu = 9.61%), and it was chosen to coat a UV LED-chip (λem = 400 nm ± 10 nm) to fabricate a red emissive LED-prototype; also, a prototype with a blend between powdered Eu-complex and cyanoacrylate glue was fabricated, and their emission behavior and radiant photostability were compared. The prototype with the doped PMMA film exhibited poorer radiant photostability than the powder prototype after 24 h of operation. Thus, the [Eu(salen)2] powder prototype gather some important characteristics to be used as a red component of warm WLEDs.