CIE Color Coordinates Research Articles

Construction of active-inert core–shell structured nanocrystals for broad range multicolor upconversion luminescence

Rare earth doped up-conversion luminescent nano-materials exhibit abundant emission colors under suitable excitation condition. In this work, NaYF4:Er/Ho@NaYF4 and NaYbF4:Tm@NaYF4 nanoparticles were synthesized by co-precipitation method. The pure red emission can be realized by the designed NaYF4:Er/Ho@NaYF4 nanocrystals and the R/Gs reach 23.3 and 25 under excitations of 980 and 1550 nm lasers, respectively. The R/G declines as the power increasing with the emission color changing from red to yellow, which is due to the quick saturation of the energy levels, radiating red emissions. Meanwhile, the emission intensity of NaYbF4:Tm@NaYF4 nanocrystals increases by 58.3 folds after encasing the inert shell NaYF4 and the CIE color coordinate reaches (0.1646, 0.0602) under 980 nm laser excitation. Furthermore, broad range multicolor from blue to red and yellow up-conversion emissions is achieved by mixing NaYF4:Er/Ho@NaYF4 and NaYbF4:Tm@NaYF4 nanocrystals, which could be applied to colorful displaying, security anti-counterfeiting and information coding.

Ce3+-Activated SrLu2Al3ScSiO12 Cyan-Green-Emitting Garnet-Structured Inorganic Phosphor Materials toward Application in Blue-Chip-Based Phosphor-Converted Solid-State White Lighting.

Phosphor-converted white-light-emitting diodes (WLEDs) with superhigh color rendering index (CRI) are the ongoing pursuit of next-generation solid-state lighting. One of the most important challenges is the limited improvement in CRI on account of the absence of a cyan component in the typical commercial combination. Here, a bright broad-band cyan-green-emitting phosphor with cubic garnet structure, SrLu2Al3ScSiO12:Ce3+ (SLASSO:Ce3+), was successfully reported, which can compensate for the absence of cyan cavity in the 480-520 nm blue-green emission region. With 439 nm blue-light irradiation, the as-fabricated SLASSO:Ce3+ phosphor yields a broad-band cyan-green emission with the maximum emission peak positioned at 525 nm and an appropriate full width at half-maximum (fwhm) of 111 nm, capable of providing more cyan emission component without sacrificing green emission. Meanwhile, the optimal SLASSO:2%Ce3+ phosphor features CIE color coordinates of (0.3254, 0.5470) with cyan-green hue, along with a high internal quantum efficiency of up to 93%. Additionally, thermal stability measurements at different temperatures reveal that the luminescence emission intensity of the proposed phosphor retains 44% of its original integral emission intensity at 423 K with respect to room temperature, while also demonstrating an excellent color stability (ΔE = 5.4 × 10-3). This work shows that the highly efficient SLASSO:Ce3+ garnet phosphor can be utilized as a potential cyan-green-emitting phosphor for filling the cyan gap, resulting in the construction of a high-quality warm WLED with high CRI for "human-centric" sunlight-like full-spectrum solid-state illumination.

Perylenedioic Acid‐Derived Carbon Dots with Near 100% Quantum Yield in Aqueous Solution for Lasing and Lighting

AbstractCarbon dots (CDs) are a burgeoning star of luminescent carbon‐based nanomaterials with emerging interest for various applications. Luminescence from the sp2‐conjugated domains in the carbon cores is considered to be the intrinsic bandgap emission of CDs, whereas the relationship between them remains poorly understood. Simultaneously, the solvent relaxation of water molecules will quench the fluorescence of CDs, thus, obtaining strong luminescence from CDs aqueous solutions remains a great challenge. Herein, a facile one‐step spatial‐confined cross‐condensation method that uses a heat‐induced self‐foaming process in ambient pressure has been developed to synthesize highly luminescent CDs with unprecedented photoluminescence quantum yield (PLQY) over 97.2% in water. The unique precursor‐derived cross‐arranged perylene skeleton in the cores hinders π–π stacking, while the hydrophobicity of the conjugated units mitigates solvent relaxation by water molecules, resulting in near‐unity PLQY in aqueous solutions, enabling this to demonstrate the first optically pumped green lasing emission in the CDs aqueous solution. Moreover, a biomaterial‐based white light emitting diode is fabricated using the CDs‐stained silks as a fluorescence conversion cover to realize a high luminous efficiency of 60.7 lm W−1 with CIE color coordinate of (0.33, 0.35).

High-brightness red-emitting Eu3+-activated Ca2LuZr2Al3O12 garnet phosphors with excellent thermal stability for near-UV-pumped white LEDs

In this work, a group of red-emitting Ca2LuZr2Al3O12:xEu3+ (x = 20%, 30%, 40%, 50%, 60%, 70% and 80%) phosphors have been prepared and their luminescence properties are studied. X-ray diffraction, excitation and emission spectra, fluorescence decay curves, CIE color coordinates, and temperature-dependent photoluminescence spectra are used to characterize these samples. All these Ca2LuZr2Al3O12:Eu3+ compounds exhibit intense red luminescence peaking at around 618 nm under 394 nm excitation. The critical concentration of Eu3+ ion is 50 mol%, and the concentration quenching mechanism has been discussed and analyzed. The CIE color coordinates of the optimal Ca2LuZr2Al3O12:50%Eu3+ sample are (0.6506, 0.3487), and it has a high color purity of 90.7%. Importantly, the emission intensity of Ca2LuZr2Al3O12:50%Eu3+ is about 1.67 times higher compared to the commercial Y2O3:Eu3+ red phosphor. What's more, Ca2LuZr2Al3O12:50%Eu3+ phosphor also displays excellent resistance to thermal quenching at elevated temperature; only 14% emission intensity is lost at 150 °C.

Novel Approach to Color‐Neutral Transparent Solar Cells: An Organic‐Si Hybrid Achieved by Laser Microhole Drilling

AbstractTransparent solar cells (TSCs) hold promise for applications in building‐integrated photovoltaics (BIPVs) and vehicles. However, existing TSCs often have compromised color neutrality and efficiency because of the distinctive colors arising from their photoactive materials. The study proposes a novel fabrication method for TSCs based on Si wafers with the average visible transmittance (AVT) controlled by creating a microhole pattern through a combination of nanosecond laser drilling and subsequent wet etching. Through this ambient‐air process, organic–Si hybrid TSCs are successfully realized by integrating an organic PEDOT:PSS layer onto this structure with a neutral color. The power conversion efficiency (PCE) is adjusted by the fraction of the perforated region, and it attained 6.20% at 30% AVT, 5.37% at 40% AVT, and 4.67% at 50% AVT. In this hybrid TSC approach, the CIE color coordinates are closely aligned with the neutral‐color points (0, 0), resulting in color rendering index (CRI) values exceeding 99. The strategy represents a significant step toward the development of efficient color‐neutral TSCs for transparent solar applications.

Bio-waste derived multifunctional carbon dots for white light generation, forensic and antibacterial applications

The synthesis of multi-colour emitting solid-state fluorescent (SSF) carbon dots (CDs) is a challenging task due to the phenomenon of aggregation-induced self-quenching. However, this study presents an efficacious method to synthesize CDs from the sap stain of the cupressus lusitanica tree (cl-CDs) via a simple one-step microwave treatment. The resulting SSF CDs exhibited a particle size of approximately 3 nm, high stability, and remarkable efficacy in light conversion when coated on a UV light emitting diode (UV LED). The ensuing coating generated white light with CIE colour coordinates of (0.33, 0.34) and a high luminescence efficiency of approximately 671 L/W. The fluorescence capabilities exhibited by the cl-CDs in response to 254 nm and 365 nm UV light excitation make them an ideal choice for developing fluorescent inks to prevent counterfeiting. Moreover, the study investigated the notable fluorescence properties of cl-CDs as a luminescent fingerprint powder for the recognition of latent fingerprints on various surfaces. Additionally, the antibacterial potential of cl-CDs was evaluated against gram-positive and gram-negative bacteria, where the cl-CDs were utilized as an antibacterial dusting powder for fluorescent imaging of latent fingerprints on different substrates. Therefore, we believe that our present work offers a plethora of exciting possibilities for the multifunctional application of SSF green CDs with significant implications in white light generation, counterfeiting prevention, forensic applications, and healthcare.

Environmental tests and reliability characterization of pixel-sized colloidal QDs for next-generation display technologies

This study investigates integrating pixelated colloidal quantum dot (QD) layers into LCDs to enhance color conversion and pixel-level enrichment for future display technologies. We developed miniature prototypes with pixel-sized QD color-converter layers seamlessly integrated into the backlight unit (BLU). The prototypes, featuring red- and green-emitting QD pixels with a single blue LED on glass substrates, underwent rigorous environmental tests such as Thermal Shock Test (TST), Thermal Cycle Test (TCT), High Temperature High Humidity Test (HHT), and Low Temperature Test (LTT). The assessment covered the uniformity of light, spectral radiance, and CIE color coordinates, revealing insights into the performance of the QD layers through the analysis of pre- and post-environmental tests. Despite a decrease in luminance, the QD layers exhibited resilience against rapid temperature variations, enduring thermal shock, and thermal cycle tests without cracking. However, high-temperature and high-humidity conditions revealed susceptibility. Low-temperature stress tests demonstrated stable color gamut coordinates with no discernible shifts. This research fills a notable gap in the existing literature by conducting comprehensive environmental tests on pixel-sized QD utilization in display technologies, providing valuable insights to enhance the stability, durability, and reliability of QD displays.

Characterization of Sm3+-activated carbonated calcium chlorapatite phosphors for theranostic applications: a comparative study of co-precipitation and hydrothermal methods.

Continuous efforts are ongoing to discover new luminescent materials with appropriate properties for applications in medicine, serving as theranostic agents for healing and bioimaging. In this paper, novel single-phase carbonated calcium chlorapatite (Ca10(PO4)5(CO3)Cl2, abbreviated as CaClAp-CO3) phosphors activated with varying concentrations of Sm3+ ions were successfully fabricated using both co-precipitation and hydrothermal methods to investigate the influence of the synthesis techniques on the physicochemical properties of these materials. The effects of doping concentration of Sm3+ ions and synthesis techniques on the structure, photoluminescence (PL), energy transfer, substitute sites, fluorescence lifetime and luminescence colour of phosphors were investigated. The synthesized phosphors were characterized by X-ray diffraction (XRD) to confirm their crystal phase structure and purity. Vibrational features and the incorporation of carbonate ions were verified using Fourier-transform infrared (FTIR) spectroscopy. The obtained materials emit reddish-orange light, primarily from the most intense 4G5/2 → 6H7/2 transition. The electric dipole to magnetic dipole transition ratio (ED/MD), CIE colour coordinates and colour purity were determined to provide additional insights into the spectroscopic attributes of the obtained phosphors. In addition, the concentration quenching was also observed, and its mechanism was proposed based on theoretical calculations showing the multipolar interactions.

Optimizing white light emission in Dy(iii) complexes: impact of energy transfer from mono and bidentate ligands on luminescence.

Complexes of dysprosium(iii) ions with 1,1,1,5,5,5-hexafluoro-2,4-pentanedione featuring various mono and bi-dentate neutral ligands have been prepared and thoroughly investigated. The synthesized complexes exhibit an octa-coordinated environment, achieved by stoichiometrically combining organic ligands and Dy(iii) ions. This octa-coordination environment of Dy(iii) ion was confirmed by FT-IR spectroscopy, thermogravimetry and elemental analysis. Near-white light (NWL) is emitted when complexes were exposed to UV radiation, indicating a significant flow of energy from the sensitizing moieties towards the Dy(iii) ion. This NWL emission might have resulted due to a balance between the intensities corresponding to emission peaks at 480 nm (blue) and 575 nm (yellow) in Dy1-Dy3. Emission spectra recorded at different excitation wavelength were utilized to study the tunability of CIE color coordinates. In addition to their high thermal stability, the complexes display bipolar paramagnetic shifts in their NMR spectra. The 4F9/2 → 6H13/2 transition, contributing ∼62% of the total emission, stands out as a promising candidate for laser amplification due to its dominance in the emission spectra. Additionally, NWL emission observed in a solid Dy(iii) complex opens intriguing possibilities for its application in next-generation white-light emitting devices.

Eu3+ singly-doped and Eu3+/Sm3+ co-doped ZnS quantum dots: structure, optical properties and energy transfer.

In this study, Eu3+ ion singly doped and Eu3+/Sm3+ ions co-doped ZnS semiconductor quantum dots (QDs) were successfully synthesized using a wet chemical method in 1-octadecene (ODE) solvent. The successful doping of Sm3+ and Eu3+ ions into the ZnS host lattice and the composition and valence of the elements present in the sample were confirmed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Structural and morphological studies revealed the presence of Eu3+-doped ZnS and Eu3+/Sm3+ co-doped ZnS QDs of about 3-4 nm size with a zinc blende structure. The Judd-Ofelt (J-O) intensity parameters of Eu3+-doped ZnS QDs were determined from their fluorescence spectra. The optical properties of Eu3+/Sm3+ co-doped ZnS QDs were studied by changing the Eu3+ ion concentration and fixing the Sm3+ ion concentration. The photoluminescence (PL) spectra of Eu3+/Sm3+ co-doped ZnS QDs were obtained at an excitation wavelength of 403 nm (6H5/2 → 6P3/2 transition of Sm3+ ions) in the 525-725 nm range. The effective energy transfer (ET) process from Sm3+ to Eu3+ ions was confirmed and explained in detail using the Reisfeld approximation and the Inokuti-Hirayama model. The CIE color coordinates of the Eu3+/Sm3+ co-doped ZnS QDs were obtained using PL spectral data. Eu3+/Sm3+ co-doped ZnS QDs exhibited a long lifetime and emitted warm red light. These interesting properties give Eu3+/Sm3+ co-doped ZnS QDs great potential for applications in photovoltaics, photocatalysis, and biomarkers.

Sustainable next-generation color converters from P. harmala seed extracts for solid-state lighting.

Traditional solid-state lighting heavily relies on color converters, which often have a significant environmental footprint. As an alternative, natural materials such as plant extracts could be employed if their low quantum yields (QYs) in liquid and solid states were higher. With this motivation, here, we investigate the optical properties of aqueous P. harmala extract, develop efficient color-converting solids through a cost-effective and environmentally friendly method, and integrate them with light-emitting diodes (LEDs). To achieve high-efficiency solid hosts for P. harmala-based fluorophores, we optically and structurally compare two crystalline and two cellulose-based platforms. Structural analyses reveal that sucrose crystals, cellulose-based cotton, and paper platforms enable a relatively homogeneous distribution of fluorophores compared to KCl crystals. Optical characterization demonstrates that the extracted solution and the extract-embedded paper possess QYs of 75.6% and 44.7%, respectively, whereas the QYs of the cotton, sucrose, and KCl crystals remain below 10%. We demonstrated that the paper host with the highest efficiency causes a blueshift in the P. harmala fluorescence, whereas the cotton host induces a redshift. We attribute this to the passivation of nonradiative transitions related to the structure of the hosts. Subsequently, as a proof-of-concept demonstration, we integrate the as-prepared efficient solids of P. harmala for the first time with a light-emitting diode (LED) chip to produce a color-converting LED. The resulting blue-emitting LED achieves a luminous efficiency of 21.9 lm Welect -1 with CIE color coordinates of (0.139, 0.070). These findings mark a significant step toward the utilization of plant-based fluorescent biomolecules in solid-state lighting, offering promising environmentally friendly organic color conversion solutions for future lighting applications.

Ultrasound-assisted nucleation and growth of hydroxyl-protected and ligand-free Cs3Cu2X5 nanocrystals with bright luminescence.

The commercial applications of lead halide perovskites are hindered by their negative environmental impact and inherent instability. Consequently, developing environmentally friendly copper-based perovskite materials is crucial for future solid-state lighting and display applications. In this study, an ultrafast high-power ultrasonic synthesis strategy was utilized to achieve uniform nucleation and growth of Cs3Cu2X5 (X = Cl, Br, I) nanocrystals (NCs) that possess remarkable luminescence properties, hydroxyl protection, and ligand-free characteristics. These Cs3Cu2X5 NCs exhibited a tunable spectral range spanning from 446 to 525 nm, accompanied by photoluminescence quantum yields (PLQYs) varying from 0.2% to 79.2%. The spectral attributes of the NCs were effectively controlled by modulating the halide type and composition. It is worth noting that density functional theory (DFT) calculations offer valuable insights into the synthesis of NCs and the selection of suitable alcohol solvents. Moreover, we successfully fabricated an efficient and stable white light-emitting diode (WLED) with a high luminous efficiency of 23 lm W-1 and CIE color coordinates of (0.3266, 0.3487). Our work provides a new strategy to synthesize Cs3Cu2X5 NCs and holds promise for their potential application in display and lighting devices.

B-embedded disulfide-bridged π-conjugated compounds: structures and optical tuning.

Two novel B-embedded disulfide-bridged π-conjugated compounds (BS-CZ and BS-N) bearing different electron donor groups (phenyl carbazole and triphenylamine) have been prepared and show different optical mechanisms. The compound BS-CZ exhibits significant multiple resonance thermal activation delayed fluorescence (MR-TADF) properties with a small singlet-triplet energy gap (ΔEST = 0.16 eV) and a narrow half-peak full width (FWHM = 33 nm), while the compound BS-N shows traditional fluorescence luminescence (FL) characteristics with a larger ΔEST (0.28 eV) and FWHM (57 nm). Time-dependent density functional theory (TD-DFT) calculations show that the lowest excited singlet state (S1) of the compound BS-CZ exhibits local excited (LE) state characteristics, while the charge transfer (CT) state characteristics can be found in S1 of the compound BS-N. Considering good optical performance, the compound BS-CZ is used as an emitting layer of the organic light-emitting diode device and achieved saturated blue emission (473 nm) with a narrow FWHM (39 nm), and CIE color coordinates of (0.12, 0.21). This work provides an important strategy for the optical mechanism regulation and photoelectric applications of B-embedded disulfide-bridged π-conjugated molecules.

Shedding Light on Eu(III) β‐Diketonate Compounds with 1,2‐Bis(diphenylphosphino)ethane Oxide Ligand: an Optical Study

AbstractA series of novel lanthanide β‐diketonate coordination compounds containing the ancillary ligand bis(diphenylphosphino) oxide (dppeO2) have been synthesized, characterized, and studied spectroscopically. The compounds of formulas Ln(β‐dik)3(dppeO2), where Ln: Eu and Gd and β‐dik ligands as tta (Ln‐1), btf (Ln‐2), bzac (Ln‐5) and tfac (Ln‐4), and Ln2(β‐dik)6(dppeO2) with ligand dbm (Ln‐3) and fod (Ln‐6). Their photophysical properties were investigated from the Judd‐Ofelt intensity parameters ( ), radiative ( ) and non‐radiative ( ) rates, intrinsic ( ) and overall ( ) quantum yields, and CIE (x,y) color coordinates. The Eu‐5 and Eu‐6 compounds have the first excited triplet states T1 (around 18802 and 18976 cm−1, respectively) almost resonant with the Eu3+ 5D0 emission level, whereas the complexes Eu‐1, Eu‐2, Eu‐3, and Eu‐4 exhibited higher T1 energies. The values were predominantly driven by the intensity parameter , suggesting more pronounced angular changes in the first coordination sphere of the Eu3+ ion. The values also exhibited significant changes with the β‐diketonate ligands. Eu‐1 showed the highest value of (60 %), indicating a more efficient intramolecular energy transfer process. On the other hand, Eu‐5 and Eu‐6 compounds showed values equal to 18.7 % and 16.5 %, respectively, which indicates the presence of luminescence quencher channels.

Full-visible-spectrum LED lighting by using a near-UV-excitable broadband blue-emitting Ca2LuHf2GaAl2O12:Ce3+ garnet phosphor

Highly efficient broadband blue-emitting phosphors are urgently needed for full-visible-spectrum white light-emitting diodes (WLEDs). Herein, we report a new highly luminescent garnet-type Ca2LuHf2GaAl2O12:Ce3+ (abbreviated as: CLHGAO:Ce3+) blue phosphor enabling full-visible-spectrum LED lighting. These CLHGAO:Ce3+ phosphors doped with different Ce3+ concentrations have been prepared by using a high-temperature solid-state reaction approach, and their phase purity, crystal structure, luminescent properties, CIE color coordinates, and quantum efficiency have been systematically studied. Importantly, CLHGAO:Ce3+ blue phosphors show a broadband excitation spectrum in the 300–450 nm spectral range peaking around 398 nm, matching well with the emission wavelengths of commercial near-ultraviolet LED chips (380–420 nm). Upon 398 nm excitation, the optimal CLHGAO:2%Ce3+ phosphor sample generates a bright broad blue emission band (emission peak: 472 nm; bandwidth: 84 nm) with high internal quantum efficiency of 79.2% and external quantum efficiency of 55.3%. Notably, the emission intensity of CLHGAO:2%Ce3+ phosphor is about 1.87 times higher compared to the commercial BaMgAl10O17:Eu2+ blue phosphor (emission peak: 451 nm; bandwidth: 53 nm). Finally, a white LED device is fabricated with a 395 nm near-UV LED chip with CLHGAO:2%Ce3+ blue phosphor and commercial (Ba,Sr)2SiO4:Eu2+ green phosphor as well as commercial CaAlSiN3:Eu2+ red phosphor, and the device demonstrates bright warm-white emission with an ultrahigh color rendering index (Ra = 95.1, R9 = 97.8, R12 = 88.4) and low correlated color temperature of 3540 K. These results show that as-developed blue-emitting CLHGAO:Ce3+ garnet phosphors with superior photoluminescence properties can potentially be used in phosphor-converted full-visible-spectrum WLEDs.

Effects of background color and restoration depth on color adjustment potential of a new single-shade resin composite versus multi-shade resin composites.

The objectives of this study was to evaluate the effects of background color and restoration depth on color adjustment potential of a new single-shade resin composite versus multi-shade resin composites. Two multi-shade resin composites (Spectrum TPH3 and Clearfil AP-X) marked A2 shade and a new single-shade resin composite (Charisma Diamond One) were tested. Four base shades (A1, A2, A3, and A3.5) of the same resin composite (Filtek Z250) were selected as different background colors. Dual specimens with 1-, 2-, and 3-mm restoration depth and single specimens of all materials were fabricated. CIE color coordinates were measured using a spectrophotometer, then color differences (∆E00) and translucency parameter (TP00) were calculated using the CIEDE2000 formula. Independent observers performed visual scoring. CAP-I and CAP-V values were calculated according to ΔE00 and visual scoring. The results revealed that CAP-I and CAP-V were significantly affected by resin composite type, background color, and restoration depth. CAP-I and CAP-V decreased as restoration depth increased at the same background color for all materials. Charisma Diamond One had the highest CAP-I and CAP-V values at all background colors and restoration depths, with the highest TP00 value. These findings demonstrated that color adjustment potential was dependent on resin composite type, background color, and restoration depth, so shade selection is indispensable for multi-shade resin composites. Charisma Diamond One exhibited the highest color adjustment potential and the most pronounced color shifting, contributing to simplifying the process of shade selection and improving the efficiency of clinical work.

Naptha-phenanthroimidazole-based blue fluorophores (y

Organic light-emitting diodes are a promising new technology for next-generation displays and lighting applications, particularly in the quest for efficient deep blue fluorophores (y= < 0.05). Despite the receipt of several reports, it remains imperative to advance the development of a deep blue emitter that can address solubility, stability, color purity, and efficiency. Eye on these challenges, herein, four new blue phenanthroimidazole and naphthalene-based derivatives, 2-(naphthalen-1-yl)-1H-phenanthro[9,10-d]imidazole(Pq-NH-NA), 2-(naphthalen-1-yl)-1-phenyl-1H phenanthro [9,10-d]imidazole (Pq-An-NA), 2-(naphthalen-1-yl)-1-(3-(trifluoromethyl)phenyl)-1H-phenanthro[9,10-d]imidazole (Pq-mF-NA), and 2-(naphthalen-1-yl)-1-(4-(trifluoromethyl)phenyl)-1H-phenanthro[9,10-d]imidazole (Pq-pF-NA) were designed and synthesized. Further, the PI molecules were structurally characterized by spectroscopic analysis, and their thermal decomposition (Td) is found to be 203–309 °C. Substitution at the N1 position of imidazole provides a facile alternative role for photophysical and electronic properties. The PI fluorophores were further characterized in solution, thin-film, and solid where the solid results are enhanced in terms of intense color emission (x = 0.158, y = 0.037). It showed a good quantum yield of 14.28 % in solution and 19.33 % in solid, indicating that fluorinated molecules lead to better performance than the rest of them. Additionally, the InGaN LED fabricated with the fluorinated molecule Pq-pF-NA emitted 425 nm with a deep blue emission and yielding CIE color coordinates (x = 0.154, y = 0.048). The film study also revealed the deep blue emission with increasing concentration of emitter (2.5 %). The observed results apprise that the synthesized fluorophores are efficient to deep blue emitters and capable candidates for organic light-emitting diodes.

Multicolor tunable emission through energy transfer in Dy3+/Ho3+ co-doped CaTiO3 phosphors with high thermal stability for solid state lighting applications

The exploration of multicolor emitting phosphors with single phase is extremely important for n-UV chip excited LED/WLED’s and multicolor display devices. In this paper, Dy3+, Ho3+ singly doped and Dy3+/Ho3+ co-doped CaTiO3 phosphor materials have been synthesized by solid state reaction method at 1473 K. The synthesized materials were characterized by XRD, FE-SEM, EDX, FTIR, PL and lifetime measurements. The PL emission spectra of Dy3+ doped CaTiO3 phosphors give intense blue and yellow emissions under UV excitation, while the PL emission spectra of Ho3+ doped CaTiO3 phosphor show intense green emission under UV/blue excitations. Further, to get the multicolor emission including white light, Dy3+ and Ho3+ were co-doped simultaneously in CaTiO3 host. It is found that alongwith colored and white light emissions, it also shows energy transfer from Dy3+ to Ho3+ with 367 nm and from Ho3+ to Dy3+ under 362 nm excitations. The energy transfer efficiency is found to be 67.76% and 69.39% for CaTiO3:4Dy3+/3Ho3+ and CaTiO3:3Ho3+/5Dy3+ phosphors, respectively. The CIE color coordinates, CCT and color purity of the phosphors have been calculated, which show color tunability from whitish to deep green via greenish yellow color. The lifetime of 4F9/2 level of Dy3+ ion and 5S2 level of Ho3+ ion is decreased in presence of Ho3+ and Dy3+ ions, respectively. This is due to energy transfer from Dy3+ to Ho3+ ions and vice versa. A temperature dependent photoluminescence studied of CaTiO3:4Dy3+/2Ho3+ phosphor show a high thermal stability (82% at 423 K of initial temperature 303 K) in the temperature range 303–483 K with activation energy 0.17 eV. The PLQY are 30%, 33% and 35% for CaTiO3:4Dy3+, CaTiO3:4Dy3+/2Ho3+ and CaTiO3:3Ho3+ phosphors, respectively. Hence, Dy3+, Ho3+ singly doped and Dy3+/Ho3+ co-doped CaTiO3 phosphor materials can be used in the field of single matrix perovskite color tunable phosphors which may be used in multicolor display devices, n-UV chip excited LED/WLED’s and photodynamic therapy for the cancer treatment.

Facilitated luminescence via pH regulation of GdF3:5%Eu3+ and NaGdF4:5%Eu3+ morphologies

Gadolinium fluoride micromaterials with eight morphologies of embroidered sphere, copper coin, rotor, irregular rhombus, cocoon pupa, rod, and hollow tubes (small and large) were synthesized in the absence of any surfactant and templating agent using gadolinium nitrate and sodium fluoroborate as raw materials and green water as a solvent. The physical and chemical properties of the products were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TG), infrared spectroscopy (FT-IR) and fluorescence spectroscopy (PL). The composition and morphology of the products were mainly regulated by pH value, with pH = 1.7, 3.7, 5.7, 7.7 and 8.7 resulting in the formation of embroidered spherical, copper coin, rotor, irregular diamond and cocoon pupae shaped GdF3:5%Eu3+ microparticles, and with pH = 9.7, 10.7 and 11.7 leading to the shaping of rod, small hollow tube and large hollow tube NaGdF4:5%Eu3+ microparticles. Their luminescent properties were also significantly distinguishable. As a whole, the luminescence of GdF3:5%Eu3+ is stronger than that of the NaGdF4:5%Eu3+ microparticles, both emitting orange‒red light. Among them, the embroidered spherical GdF3:5%Eu3+ microparticles prepared at pH = 1.7 showed the strongest luminescence with a fluorescence lifetime of 10.11 ms and CIE color coordinates of 0.6061 and 0.3934. Possible mechanisms for the preparation of gadolinium fluorides with various morphologies at different pH values were analyzed, and the reasons for their effect on fluorescence properties were further investigated. GdF3 micromaterials not only provide the basis for a wide range of applications in upconversion luminescence but also have potential applications in downconversion luminescence, providing good research support for the synthesis and application screening of micronanomaterials containing gadolinium for morphology modulation.

Efficient broadband yellow-emitting Mg2.5Lu1.5Al1.5Si2.5O12:Ce3+ garnet phosphors for blue-light-pumped white light-emitting diodes

The discovery of yellow-emitting phosphors with higher luminescence intensity and wider bandwidth than the commercial Y3Al5O12:Ce3+ (YAG:Ce3+) phosphor upon blue light excitation remains one of the significant challenges for establishing human-centered warm white light-emitting diode towards high-performance illumination. Herein, we innovatively synthesized a novel Ce3+-activated broadband yellow-emitting garnet phosphor of Mg2.5Lu1.5Al1.5Si2.5O12:Ce3+ (MLASO:Ce3+) via conventional high-temperature solid-state reaction method. The as-prepared MLASO:10%Ce3+ garnet sample possesses a cubic structure with Ia3‾d space group and lattice parameters of a = b = c = 11.85098 Å and V = 1664.421(0.044) Å3. Luminescence spectroscopy tests indicates that the optimal MLASO:10%Ce3+ yellow-emitting phosphor features 1.2 times higher relative integral luminescence intensity and an impressive full width at half maximum (FWHM) of up to 145 nm with respect to the most extensively available commercial YAG:Ce3+ phosphor (FWHM = 122 nm) under the identical blue light irradiation, which can provide more red-components for improving color rendering index. Additionally, the CIE color coordinates and a satisfactory internal quantum efficiency are determined to be (0.4751,0.5028) and 74%, respectively. More importantly, the representative optimal sample can preserve 77% luminescence emission intensity at a 423 K high temperature thermal treatment environment compared to the ambient temperature. As a result, this study sheds light on newly discovered broadband yellow-emitting MLASO:10%Ce3+ garnet phosphor containing more of the red chromatic spectrum can sever as one of the promising color-conversion-materials in high-performance white LEDs with high color rendering index for healthy solid-state lighting.