Color Rendering Index Research Articles

Orange-red-emitting (Sr,Ba)3SiO5:Eu2+ phosphor-in-glass film for enhanced color rendering of laser lighting

Nitride red-emitting materials exhibit severe luminance saturation and are thus not suitable for achieving enhanced color rendering in laser lighting applications. The silicate luminescent material (Sr,Ba)3SiO5:Eu2+ displays excellent stability and can emit orange-red light when excited by blue laser light, making it a promising candidate for realizing high-performance laser lighting. In this study, (Sr,Ba)3SiO5:Eu2+ phosphor-in-glass (PiG) films were prepared on a sapphire substrate, and the influences of preparation temperature, mass ratio of phosphor to glass frit (PtG ratio), and film thickness on the application performance of PiG film were analyzed. The (Sr,Ba)3SiO5:Eu2+ PiG film with a PtG ratio of 1:1 and a film thickness of ∼50 μm prepared at 475 °C exhibited optimal comprehensive luminescence performance. This film exhibited a luminous saturation threshold of 5.98 W/mm2, a maximum luminous flux of 372.3 lm, and a luminous efficiency of 62.3 lm/W at the luminous saturation threshold. The maximum luminous flux of the (Sr,Ba)3SiO5:Eu2+ PiG film was 77.6% higher than that of the CaAlSiN3:Eu2+ nitride PiG film. Finally, through the incorporation of green-emitting YAGG:Ce3+ phosphor into the (Sr,Ba)3SiO5:Eu2+ PiG film, laser-driven white light with a luminous flux of 531.7 lm and a high color rendering index (CRI) of 83.4 was realized.

Unveiling the underlying mechanism behind the greatly increased properties of Cu(I)-perovskites and their applications for durable WLED and multi-model encryption/decryption

Methods allowing all-inorganic perovskites to be performed on exceptional photophysical property with ultrastability are potentially important. Especially, the development of Cu(I)-perovskites with high photoluminescence quantum yield (PLQY) and stability remains challenge. Herein, a facile and reliable strategy towards CsCu2I3 nanocrystals composites (CsCu2I3/P-NCCs) by ion–dipole interaction induced space-confined growth within polymer is reported. The greatly enhanced PLQY and superior stability against external stimuli (i.e., UV-irradiation, heat, oxygen/moisture, polar solvents) are primarily attributed to the strong ion–dipole interaction (ΔG = −10.20 eV) between polyethyleneglycol (PEG) and precursor/perovskites as revealed by DFT simulation and experiments, which is unidentified in previous literature. The exceptional optical performance and stability enable the promising application of CsCu2I3/P-NCCs in white light-emitting diode (WLED) and anti-counterfeiting, delivering unprecedented color-rendering index (CRI of 95.4) and long half-life time (984h) under continuous illumination, as well as compositional engineered multi-model encryption/decryption. This work demonstrates that the association of weak force has significant influence on perovskites, providing an original principle for the synthesis and application of strongly-emissive and highly-stable perovskites.

All-Inorganic Lead-Free Doped-Metal Halides for Bright Solid-State Emission from Primary Colors to White Light.

Metal halides have been explored with the aid of strong photoluminescence for optical and optoelectronic applications. However, the preparation of lead (Pb)-free solid-state emitters with high photoluminescence quantum yields (PLQYs) and tunable emission remains exceptionally challenging. Herein, we report metal ion (Cu(I), Mn(II), and Sn(II))-doped Cs3ZnI5 single crystals that are primary color (violet, green, and orange/red) emitters with extremely high PLQYs. Whereas the Mn-doping leads to bright green emissions with 100% PLQY, the Cu- and Sn-doping give rise to blue and red emissions with PLQYs of 57 and 64%, respectively. Interestingly, higher Mn doping results in white light emissive crystals as a side product, which are found to be Mn-doped CsI single crystals. The bright white light emissive crystals can be synthesized in a pure form in large quantities and exhibit a high color rendering index (CRI) of 78 and CIE coordinates of (0.30, 0.38), which are close to daylight conditions. To the best of our knowledge, this is the first demonstration of white light emission from a complete inorganic system. Importantly, the single crystals of all colors exhibit high long-term stability as their PLQY remains unchanged even after 2 months of preparation, and are thermally stable up to 600 °C.

Improved Luminous Efficiency of AgInS2 Quantum Dots and Zeolitic Imidazolate Framework-70 Composite for White Light Emitting Diode Applications.

The application of multiple quantum dots (QDs) in the field of white light emitting diodes (WLEDs) is still an important challenge due to their low luminous efficiency and quenching phenomenon. In this paper, we prepared AgInS2 QDs/zeolitic imidazolate framework-70 (AIS/ZIF-70) composite by a microwave hydrothermal method. Owing to the high porosity and stability of ZIF-70, it could effectively prevent quenching issues due to the aggregation of QDs. Since the ZIF-70 and QDs were chemically bonded, the formation of the ZnS layer could effectively passivate the surface defect and thus the quantum yield reached 21.49 % in aqueous solution. The luminous efficiency (LE) of the assembled AIS/ZIF-based WLED was reinforced by 6.8 times with a molar ratio of AgIn/Zn=18, i. e. at 5.26 % molar fraction of ZIF-70. Moreover, the color rendering index (CRI) and correlated color temperature (CCT) of AIS/ZIF-based WLED were 84.3 and 3631 K, respectively, indicating its potential application in solid-state lighting.

Multi-color luminescence of Sm3+ -doped Na2 YMg2 V3 O12 phosphor potentially applicable in white-LEDs.

A novel multi-color emitting Na2 YMg2 V3 O12 :Sm3+ phosphor was synthesized using a solid-state reaction, and its crystal structure, luminescence properties, and thermal stability were studied. Charge transfer within the (VO4 )3- groups in the Na2 YMg2 V3 O12 host led to a broad emission band between 400 and 700 nm, with a maximum at 530 nm. The Na2 Y1-x Mg2 V3 O12 :xSm3+ phosphors exhibited a multi-color emission band under 365 nm near-ultraviolet (near-UV) light, consisting of the green emission of the (VO4 )3- groups and sharp emission peaks at 570 nm (yellow), 618 nm (orange), 657 nm (red), and 714 nm (deep red) of Sm3+ ions. The optimal doping concentration of Sm3+ ions was found to be 0.05 mol%, and the dipole-dipole (d-d) interaction was primarily responsible for the concentration quenching phenomenon. Using the acquired Na2 YMg2 V3 O12 :Sm3+ phosphors, commercial BaMgAl10 O17 :Eu2+ blue phosphor, and a near-UV light-emitting diode (LED) chip, a white-LED lamp was designed and packaged. It produced bright neutral white light, manifesting a CIE coordinate of (0.314, 0.373), a color rendering index (CRI) of 84.9, and a correlated color temperature (CCT) of 6377 K. These findings indicate the potential of Na2 YMg2 V3 O12 :Sm3+ phosphor to be used as a multi-color component for solid-state illumination.

Efficient blue-light-excited cyan-emitting CaLu2HfScAl3O12:Ce3+ phosphors for full-visible-spectrum warm-white LEDs

Bright cyan-emitting phosphor is indispensable to fill the cyan gap for the fabrication of full-visible-spectrum warm-white light-emitting diodes (LEDs) with high color rendering index (CRI). In this study, we demonstrate a novel efficient cyan-emitting Ce3+-activated CaLu2HfScAl3O12 (CLHSA) garnet phosphor for application in blue-light-excited full-spectrum warm-white LEDs. CLHSA:Ce3+ phosphors show broadband excitation spectra in the 300–470 nm spectral range with a maximum peak at 408 nm, indicating they can be efficiently pumped by the blue LED chips. The optimal doping concentration of Ce3+ ions is found to be 1 mol%. Upon 408 nm excitation, the optimal CLHSA:1%Ce3+ phosphor gives rise to a bright broadband cyan emission (peak position: 498 nm; bandwidth: 97.5 nm) with CIE chromaticity coordinates of (0.2196, 0.4265) and high photoluminescence quantum yield of 64.5%. Finally, we have fabricated a blue-light-excited high-CRI warm-white LED device by employing the CLHSA:1%Ce3+ cyan phosphor, commercial YAG:Ce3+ yellow phosphor and commercial CaAlSiN3:Eu2+ red phosphor as well as a 450 nm LED chip, which demonstrates a bright warm-white light emission with a high CRI (Ra = 92.6), a low correlated color temperature (3660 K), and good CIE chromaticity coordinates of (0.3993, 0.3939) as well as a high luminous efficacy of 45 lmW−1. Therefore, this newly discovered efficient cyan-emitting CLHSA:1%Ce3+ phosphor is promising for application in blue-chip-pumped full-visible-spectrum warm-white LEDs with high CRI values.

A yellow-green-emitting graphitic-C3N4 derivative consisting of 1,4-phenylene-inserted heptazine units: Preparation and application as a metal-free phosphor for white LEDs

To develop non-rare-earth or metal-free phosphors for white light-emitting diodes (WLEDs) are very significant and forward-looking. Here, a yellow-green-emitting g-C3N4 derivative (p-Ph-g-C3N4) consisting of 1,4-phenylene-inserted heptazine units was successfully prepared by 6,6'-(1,4-phenylene)bis(1,3,5-triazine-2,4-diamine) via thermal polymerization. Its emission is mainly located at 450–700 nm with the maximum wavelength (λem,max) of 536 nm, its quantum yield (QY) is 15.7% (λex = 430 nm) which is much higher than that of bulk g-C3N4 (ca. 5%). Under the excitation of 430 nm blue-emitting GaN-based chips (ca. 4.0 lm·W−1), p-Ph-g-C3N4 together with non-rare-earth red-emitting K2SiF6:Mn4+ as phosphors, a series of cold, neutral, and warm WLEDs with good performances were fabricated. As for the best one, its color rendering index (CRI) is 84.3, correlate color temperature (CCT) is 5702 K, luminous efficiency (LE) is 5.40 lm·W−1, moreover, its CIE value (0.30, 0.34) is very close to (0.33, 0.33) of pure white light. The research results indicate p-Ph-g-C3N4 can be used as an efficient metal-free quasi-green phosphor for WLEDs.

Two Novel Two-Dimensional Organic-Inorganic Hybrid Lead Halides with Broadband Emission for White-Light-Emitting Diodes.

Low-dimensional organic-inorganic metal halides (LOMHs) recently have attracted much attention due to their tunable crystal structures and excellent photoelectric properties. The configuration and arrangement of organic cations in LOMHs have significant effect on the structure of inorganic frameworks and luminescence properties. In this work, we systematically explored the "spatial effect" and "hydrogen bonding effect" of organic cations on the structure and properties of LOMHs, by synthesizing three LOMHs including (N-AD)PbCl4, (N-AD)2Pb2Br7, and (N-AD)4Pb3I12 (N-AD: N-acetylethylenediamine, C4H10N2O). Specifically, (110)-oriented two-dimensional (N-AD)PbCl4 and (N-AD)2Pb2Br7 with manifest blue-white emissions, originating from the free excitons (FEs) and self-trapped excitons (STEs), respectively. The UV-pumped light-emitting diode (LED)-based on (N-AD)2Pb2Br7 was prepared, and the highest color rendering index (CRI) and correlated color temperature (CCT) were up to 80 and 4484 K, respectively. This proves its potential application in solid-state lighting.

Cation engineering in low-dimensional organic-inorganic copper halides for high color rendering index WLEDs

Searching for single-component white-light emitting materials with excellent color rendering index (CRI) is significant to the development of white-light emitting diodes (WLEDs). Herein, we introduce three different cations with increasing steric hindrance to develop novel luminescent low-dimensional organic copper halides: one-dimensional (1D) ETMACu2I3 (ETMA: ethyltrimethylammonium), 1D TEACu2I3 (TEA: tetraethylammonium), and zero-dimensional (0D) TBMACuI2 (TBMA: tributylmethylammonium). The dimensionality of the prepared copper halides decreases with the increase of the steric hindrance of the organic cations. Meanwhile, the photoluminescence spectra become broader. The two 1D compounds exhibit weak single broad emission originating from self-trapped excitons (STEs) and defects. Interestingly, 0D TBMACuI2 emits bright warm white light with dual emission bands. The mechanism of the unique dual emission is unveiled by systematic spectroscopic study including temperature-dependent and femtosecond transient absorption spectroscopies. Two spin-triplet STE states contribute to the intriguing dual emission. A WLED based on TBMACuI2 can exhibit an ultra-high CRI of 95.7, which is promising for single-component white-light emitting applications.

Enhancement of color rendering index of stable lead-free perovskite WLEDs through incorporating green carbon dots

In this work, the carbon quantum dots@Cs2NaInCl6 (CDs@CNC) composites are presented by a facile solution synthesis. The obtained CDs@CNC composites maintain the octahedral morphology of original CNC host and the characteristic functional groups of original CDs. As a result, the rare-earth-free CDs@CNC composites exhibit green light emission with good stability for UV irradiation, heat, and humidity. In addition, CDs were combined with ion-doped CNC to obtain multicolor phosphor and the corresponding white light emitting diode (WLED) devices were fabricated by coating composites on commercial UV chips. The color render index (CRI) of WLEDs increases significantly from 66.24 to 90.95 while the cold-warm white fluorescence can be flexibly tuned by the change of excitation wavelength. The combination of CDs and double perovskites provide a new route to design white light emission phosphors, which could lead to the fabrication of next generation high-quality lighting devices.

Realizing full-spectrum LED lighting with a bright broadband cyan-green-emitting CaY2ZrGaAl3O12:Ce3+ garnet phosphor

Full-visible-spectrum white light-emitting diodes (LEDs) with ultrahigh color rendering index (CRI), which are capable of offering a light source that mimics natural sunlight, have great application potentials in healthy lighting, high-resolution displays, and plant growth lighting. However, cyan gap in the 480–520 nm wavelength range is commonly existed in the emission spectra of traditional phosphor-converted white LEDs, and thus it is urgent to develop high-performance cyan-emitting phosphors to close this spectral gap for realizing full-visible-spectrum LED lighting. Herein, we demonstrate a new efficient cyan-green-emitting Ce3+-activated CaY2ZrGaAl3O12 garnet phosphor for near-ultraviolet (near-UV) pumped full-visible-spectrum warm-white LEDs. The CaY2ZrGaAl3O12:Ce3+ cyan-green phosphor has a cubic structure with the space group Ia3‾d and lattice parameters of a = b = c = 12.39645(8) Å and V = 1886.08(6) Å3. Ce3+ doping concentration dependent luminescence properties have been studied, and the highest emission intensity is obtained at 1 mol%. The optimal CaY2ZrGaAl3O12:1%Ce3+ sample shows a broad excitation band in the 300–490 nm wavelength range with peak at 409 nm due to the 4f→5d transition of Ce3+ ions. Upon 409 nm excitation, CaY2ZrGaAl3O12:1%Ce3+ produces a wide cyan-green emission band in the 425–750 nm spectral range with a peak at 514 nm and a full width at half-maximum of 110 nm owing to the 5d→4f transition of Ce3+ ions, and the corresponding CIE color coordinates and internal quantum efficiency are determined to be (0.2802, 0.4856) and 56%, respectively. Furthermore, the resulting CaY2ZrGaAl3O12:1%Ce3+ phosphor exhibits good thermal stability, and its emission intensity at 423 K is about 58% of that at 303 K. Finally, a white LED device is fabricated by employing a 395 nm near-UV chip with the phosphor blend of commercial BaMgAl10O17:Eu2+ blue phosphor, as-prepared CaY2ZrGaAl3O12:1%Ce3+ cyan-green phosphor, commercial (Ba,Sr)2SiO4:Eu2+ green phosphor and commercial CaAlSiN3:Eu2+ red phosphor, which exhibits a bright full-spectrum warm-white light with low color correlated temperature of 3334 K and ultrahigh CRI values (Ra = 97, R9 = 95.3, R12 = 90.1) for 20 mA driving current. This work provides a new perspective in designing luminescent materials for high-color-quality full-visible-spectrum LED lighting.

Tunable white light photoluminescence of a single phase Tm3+/Tb3+/Eu3+ codoped GdPO4 phosphor

The present study describes the production of triply-doped GdPO4 and its optical characteristics. Structural information of the prepared material has been investigated by using X-ray diffraction and Fourier transform infrared spectroscopy. The material synthesized crystallizes into a single monoclinic crystal of space group P 21/n. The excitation curves of photoluminescence of single doped GdPO4: Tm3+, Tb3+, and Eu3+ are recorded and their emission spectra are analyzed. Triple-doped material emits multi colour light after a single UV stimulation. White light emission was seen in both triply-doped GdPO4 with variable Tm3+ concentration and triply-doped GdPO4 with variable Eu3+ concentration. GdPO4 doped with Tb3+ (7 mol%), Tm3+ (1.5 mol%), and Eu3+ (2 mol%) has colour coordinates (x = 0.3290, y = 0.3291) approximately near the value of typical white colour coordinates (x = 0.333, y = 0.3333). Furthermore, the transfer of energy in Tm3+, Tb3+ and Eu3+ in triple doped phosphor with varying Eu3+ concentrations was explained. Electric dipole-dipole interaction is used to justify and describe the process of energy transfer from Tb3+ to Eu3+. Decay time measurements were performed to explain energy transfer. Colour rendering index (CRI), Corelated colour temperature (CCT), Quantum efficiency and thermal stability of the prepared phosphor was calculated. All these parameters infer that GdPO4 doped with Tm3+, Tb3+ and Eu3+ may have potential application in white LEDs.

Towards efficient blue Eu2+ activated pyrophosphate phosphor for warm white LED applications

A blue-emitting LiCsBaP2O7:Eu2+(LCBPO:Eu2+) pyrophosphate phosphor prepared by solid-state synthesis that emits bright blue light with a first-rate internal quantum efficiency and high color purity is reported. Furthermore, when heated from 298 K to 473 K, LCBPO:0.015Eu2+ phosphor exhibits excellent color stability. Impressively, LCBPO:0.015Eu2+ blue phosphor exhibits exceptional stability against air exposure over a month. Fabricating a near-ultraviolet (n-UV) pumped pc-wLED using LCBPO:0.015Eu2+ along with green (Sr,Ba)2SiO4:Eu2+ and red (Ca,Sr)AlSiN3:Eu2+ phosphors demonstrates a well distributed warm white light with a high color-rendering index (Ra) of 91.7, a low correlated color temperature (CCT) of 3382 K and a high luminous efficiency (LE) of 26.1 l m/W. The high-performance optical characteristics, straightforward synthesis procedures and economical initial materials cost of LCBPO:Eu2+ support the potential of this material for usage in warm white LED-based lighting systems.

Blue LED (InGaN)-driven yellow and red emitting phosphor for white light generation

Phosphor converted white LED using a yellow and red emitting material is investigated. For this we prepare K2SiF6:Mn4+ as red emitting phosphor via wet chemical technique. The white LED (w-LED) fabricated using blue InGaN LED chip (CREE 460 nm) coated with Y3Al5O12:Ce3+ and K2SiF6:Mn4+ phosphor. The effect of K2SiF6:Mn4+ phosphor as red emitting material in combination with blue InGaN LED chip (CREE 460 nm) coated with Y3Al5O12:Ce3+ phosphor is also investigated. The Commission International de I’Eclairage (CIE) coordinates and color rendering index (CRI) were also studied as a function of K2SiF6:Mn4+ content. The w-LED fabricated using blue InGaN LED chip (CREE 460 nm) coated with Y3Al5O12:Ce3+ and K2SiF6:Mn4+ phosphor shows a CIE value (x = 0.31, y = 0.33) with 78.1 CRI.

Cation defects succeed in triggering super stability of narrow-band blue-emitting phosphors Ca3Sc2Si3O12: Bi3+ for backlighting display application

High-performance white light-emitting diodes (WLEDs) used for backlighting display applications require innovative and thermally stable narrow-band emission phosphors, particularly non-rare-earth Bi3+-activated phosphors. In this study, we demonstrate a defect-engineering strategy to create novel anti-thermal quenching phosphors Ca3Sc2Si3O12: xBi3+ (CSSO: xBi3+). Through structure refinement of CSSO: 0.06Bi3+ phosphor, we found that Bi occupies both Ca and Sc sites in the CSSO lattice. Direct visualization of atomic-resolution TEM and thermoluminescence spectra confirmed the formation of point defects due to the non-equivalent substitution of Ca2+ for Bi3+. Fluorescent-decay analysis revealed that two luminescence sites contribute to the blue-emitting of CSSO:Bi3+ phosphors. CSSO: 0.06Bi3+ phosphor exhibits outstanding thermal stability, with an integrated emission intensity of 103.6% at 423 K compared to that at 298 K. However, the addition of Li or Na as charge compensators reduced cationic defects, leading to a decrease in thermal stability. We believe that VCa″ defects are primarily responsible for the anti-thermal quenching behavior of CSSO: xBi3+ phosphors. An optimized CSSO: 0.06Bi3+ phosphor-based WLED displays a high color rendering index (CRI) of 90 and a wide color gamut (90% National Television System Committee (NTSC) standard), indicating its potential for use in industrial applications as a backlighting display.

Composition engineering of lead-free double perovskites towards efficient warm white light emission for health and well-being

Lead-free halide double perovskites (DPs) [A2B(I)B(III)X6] (A: monovalent cation, B(I): monovalent cation, B(II): trivalent cation, X: halide anion) has drawn tremendous attention because of their environmental-friendliness and high stability compared to traditional lead-based perovskites ABX3 (A: monovalent cation; B: Pb2+; X: halide anion). The optoelectronic properties of DPs are, however, compromised. This work provides a methodology for improving the photophysical properties of DPs and achieving high-efficiency warm white light emission. First principles density functional theory (DFT) was used in material design and the ligand-free synthesis of halide DP Cs2Ag1−xKxIn0.875Bi0.125Cl6 (x ≤ 0.60) via a facile recrystallization process was demonstrated. The compositional tuning of K+ to Ag+ resulted in an improvement in photophysical properties. Independent of K+ content, all the samples exhibit strong absorption at a wavelength of λmax ∼ 375 nm with a direct bandgap which is consistent with our DFT calculation results. Broadband photoluminescence (PL) emission profiles covering the spectra from blue to deep red (405–820 nm at λmax ∼ 629 nm) were observed. Besides, with an optimized K+ alloying content of 0.20, the optical performance of these halide DPs was impressively regulated, demonstrating improved photoluminescence quantum yield (PLQY) of host Cs2AgInCl6 crystals from ∼ 2.70 % (x = 0) to ∼15.96 % (x = 0.20), due to increased radiative recombination of self-trapped excitons. the highest report for such structures. It also shows high stability over 180 days. Furthermore, the use of blue-emitting CsPbBr3 and DP Cs2Ag0.80K0.20In0.875Bi0.125Cl6 as color conversion layers in white light-emitting diodes (LEDs) demonstrates that high-quality white light emission with the CIE color coordinate of (0.387, 0.385) and a correlated color temperature (CCT) of 3878 K, color rendering index (CRI) of 85, and luminous efficacy of radiation (LER) of 214 lm/W. Hence, the research work provides insight into realizing environmentally friendly and high-efficiency white light emission with high color quality by using earth-abundant elements and the low-cost synthesis method.

Hybrid sulfurothioate-based electrolyte improving aesthetics, performance, and stability of transparent NIR-dye-sensitized solar cells

Enhancing performance, stability, and aesthetics is crucial for the development of transparent photovoltaics (TPV). In TPV, aesthetics are equally or even more important than performance because social acceptance requires maintaining aesthetics to a high level. In this work, we report a colorless hybrid electrolyte consisting of a thioate/iodide mixture. When integrated into wavelength-selective near-infrared-dye-sensitized solar cells (NIR-DSSCs), this electrolyte improves the power conversion efficiency (PCE) to up to 2.9% with a scattering layer and 2.1% in a transparent cell under AM1.5G conditions. It also reaches as high as 96% PCE retention over 1,800 h and confers an outstanding aesthetic level, up to 80% average visible transmittance (AVT), a color rendering index (CRI) of 96, and color purity as low as 14%, thus equaling the aesthetics of a double-glazed glass window.

Zr4+ and Bi3+ codoped Cs2Ag0.3Na0.7InCl6 double perovskite for single-composition white-light emitting phosphors and multimodal optical anti-counterfeiting

Single-composition white-light emitter with excitation-dependent emissions is highly desired for phosphor-converted white-light emitting diodes (WLEDs) and optical anti-counterfeiting, in terms of the optical self-absorption and degeneration induced by the different components. However, the rational regulation of excitation-dependent multi-emissions in single perovskite materials is still a grand challenge. Herein, Bi3+ and Zr4+ codoped Cs2Ag0.3Na0.7InCl6 double perovskite microcrystals (DPMCs) were reported for single-composition white-light emitting phosphors and multimodal optical anti-counterfeiting. As a result, the photoluminescent quantum yield (PL QY) and color rendering index (CRI) were recorded up to 80.3% and 95.8, respectively. Specifically, under ultraviolet (UV) excitation at 365 nm, the Zr4+-doped DPMCs exhibited distinct emission profiles with single broad band centered at ∼570 nm for various Zr4+ doping concentrations, which could be attributed to the self-trapped exciton (STE) emission of the host. While the DPMCs show dual emission bands centered at ∼470 and ∼570 nm excited at 254 nm, which originates from the [ZrCl6]2- octahedral and STE, respectively, and their integral PL intensity ratio can be gradually adjusted by the content of Zr4+. The broad multicolor emissions with color kinetic features of the single-composition DPMCs offer exciting opportunities for constructing WLEDs and multimodal optical anti-counterfeiting.

Wide Range CCT Laser-Based Illuminant With High Efficiency and Excellent Optical Performances

A wide range correlated color temperature (CCT) white light laser-based illuminant (LBI) consisting of dual blue laser diodes (LDs), yellow phosphor color converters and red LDs has been proposed. In addition to the conventional 455 nm blue LDs-pumped phosphor color converters, another blue LD is utilized for the adjustment of CCT and improvement of the color rendering index (CRI). Considering systematic manipulation of the power ratio of LDs and peak wavelength of tuning blue LDs from 440 nm to 480 nm, different combinations of spectral power distributions of LBIs were simulated. It shows that an optimized 465 nm tuning blue LD is employed to achieve a balance between optical performances and blue light hazard efficiency of radiation (BLHER). The first practical LBI comprised of Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> :Ce <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> (YAG:Ce <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> ) phosphor color converters and three monochromatic LDs of 455 nm, 465 nm and 635 nm was fabricated based on the stated simulations. In good agreement with the simulation results, the LBI has simultaneously achieved an excellent CRI beyond 85, a high luminous flux of approximately 2000 lm and a high luminous efficiency of radiation (LER) of over 300 lm/W at the fairly wide CCT range of 3300 K to 6000 K. The low BLHER was consistently below 0.237. The circadian action factor (CAF) was between 0.36 and 0.83, and its tunability was 2.31 above the CCT range, which favors the entrainment of circadian rhythm. Therefore, this work demonstrates a promising method for providing high-quality and human-oriented white light sources in applications requiring great brightness.

Key role of Nb5+ in achieving water-resistant red emission in K2Ta1-xNbxF7:Mn4+ phosphors

Mn4+-activated fluoride is one of the most important red phosphors for white light-emitting diodes (WLEDs) with high color rendering index (CRI). Due to a lack of water resistance, their potential applications are limited. Although surface coating strategies improve the waterproof stability of fluoride red phosphors, they have downsides. It was found that Nb5+ plays an important role in improving the water resistance of Mn4+-activated oxyfluorides by preventing the hydrolysis of [MnF6]2-. In this work, the influence of Nb5+ on the waterproof stability of Mn4+-activated fluorides was explored. A set of synthesized K2Ta1-xNbxF7:Mn4+ phosphors exhibit tunable and superior water resistance. The photoluminescence (PL) intensity of the representative sample K2Ta0.6Nb0.4F7:5%Mn4+ remains nearly 100% of its initial value even after being immersed in water for 60 min, which is significantly higher than the commercial K2SiF6:Mn4+ red phosphor (8.7%). Our findings open up new possibilities for the development of waterproof fluoride red phosphors.