Solid Solution Phosphors Research Articles

Eu2+-activated hexagonal aluminate solid solution phosphors with high quantum efficiency and anti-thermal quenching for pc-LEDs

The luminescence quantum efficiency and thermal stability are important parameters for phosphors when applied in phosphor-converted white light-emitting diodes (pc-LEDs). A facile solid solution strategy was applied to improve the quantum efficiency and thermal stability based on Na-β-Al2O3:Eu2+. Ba2+, Mg2+, and Ge4+ are introduced to replace Na+ and Al3+ simultaneously, besides the substitution of Na+ by Eu2+. X-ray powder diffraction, scanning electron microscopy combining elemental mapping indicate the formation of solid solution from Na-β-Al2O3:Eu2+ and BaMgAl10O17:Eu2+. The internal and external quantum efficiencies (IQE, EQE) both increase through solid solution with nearly unchanged blue emission at 468 nm. The IQE and EQE values of nominal Na1.6-xBaxAl11-3xMg2xGexO17+δ:0.2Eu2+ (x = 0.3) are as high as 90.4 % and 68.1 %, respectively. Furthermore, the thermoluminescent curves suggest that the defects decrease by introducing Ba2+, Mg2+, and Ge4+ ions. Therefore, the anti-thermal quenching degree decreases, resulting in better thermal stability. The proto-type white pc-LED based on the as-synthesized blue phosphor has a color-rendering index of 87, and nearly unchanged emission profile versus driving currents. The solid-solution phosphors show their potential as blue-emitting component for white pc-LEDs.

Luminescence enhancement of near-infrared Cr3+ doped solid solution phosphor via Al3+ substitution for light-emitting diode applications

The luminescence enhancement of near-infrared (NIR) emissive material is critical in emerging applications. In this work, we have prepared an NIR-emitting K2NaSc1-x-yAlxF6:yCr3+ (denoted as KNS1-x-yAxF:yCr) solid solution phosphor via the introduction of Al3+, enhancing luminescence in a high-temperature solid-state reaction. The resultant solid solution phosphor exhibited a broad NIR emission band with a high internal quantum efficiency (IQE = 81.1 %) and an enhanced photoluminescence thermal stability (93 % at 423 K) under 432 nm excitation. When compared with the Al-free sample, the IQE and thermal stability are increased by 45.9 % and 22.4 %, respectively. The optimal Cr3+ and Al3+ doping content has been determined and a composition-optimized KNS0.70A0.25F6:0.05Cr phosphor is demonstrated by fabricating an NIR pc-LED device as a light source for light-emitting diode applications.

Band-gap engineering enabled emission switch in solid-solution phosphors LiIn1-xScxGeO4:Bi3+ for spectral-temporal anti-counterfeiting

The interaction between matrix lattice and doped activator has long been pivotal topic in the research of the state-of-the-art functional materials, particularly luminescent materials. With the ceaseless development of advanced anti-counterfeiting, there are imperative need for developing luminescent materials with wide emission tunability, excellent visibility, and adjustable persistent luminescence. Herein, we present a paradigm to obtain great emission tunability in a solid-solution phosphors LiIn1-xScxGeO4:Bi3+ (x = 0–1) via band-gap engineering. With the increase in Sc content, the band-gap enlarges, causing the Bi3+ emissions gradually shift from 580 to 456 nm. As Sc substitution continues, the Bi3+ emissions transfer from the metal-to-metal charge transfer band to the inter s-p transition, resulting in a rapid shift in emission from 456 to 356 nm. This emission shift not only achieves a record total tunability of 224 nm among Bi3+-doped solid-solution phosphors but also an informative band-gap dependent emission mechanism of the Bi3+ activator. Furthermore, the samples gradually exhibited a persistent luminescence through the substitution process, attributed to the increasing traps by the thermoluminescence analysis. Leveraging these unique spectral properties, we designed two types of patterns that can be distinguished from color and time within the visible light range, demonstrating that the obtained phosphors can serve as promising candidate materials for spectral-temporal anti-counterfeiting.

Crystal field optimization, luminescence enhancement and thermal stability of novel K2NaAl0.4Ga0.6F6:Mn4+ solid solution red phosphor for high-performance warm WLED

Mn4+-doped fluoride phosphors have important application value in the background light and WLED lighting fields. Therefore, the synthesis of efficient and stable Mn4+-doped red phosphor is of great application value. In this study, a series of red-emitting K2NaAl1-yGayF6:xMn4+ (y = 0, 0.2, 0.4, 0.6, 0.8 and 1) (x = 0.01, 0.03, 0.05, 0.07 and 0.09) solid solution phosphors are successfully synthesized by simple coprecipitation method. The synthesis strategy of simple crystal structure optimization is proposed to realize simultaneously the crystal field optimization, luminescence enhancement and thermal stability of red phosphor. The calculation and theoretical analysis of crystal field strength are used to prove that solid solution matrix K2NaAl0.4Ga0.6F6 is the most ideal matrix material. X-ray powder diffraction, energy-dispersive X-ray spectrometer and scanning electron microscope are employed to determine the crystal structure, composition and morphology of all samples. Optical properties are characterized using excitation spectra, emission spectra and fluorescence lifetime curves. Moreover, the CIE coordinates of red-light show that the phosphor has low correlated color temperature and excellent color purity. Intriguingly, the as-prepared K2NaAl0.4Ga0.6F6:Mn4+ phosphor possesses admirable thermal quenching behavior and color stability at high temperature. At a temperature of 423 K, the photoluminescence intensity can be maintained at 52 % of the original intensity (298 K). The activation energy, the chromaticity shift and chromaticity coordinate variation are also systematically calculated. More importantly, A high-performance warm WLED with low correlated color temperature (CCT = 3982 K) and high color rendering index (Ra = 93.7) is achieved by using K2NaAl0.4Ga0.6F6:Mn4+ as a red-emitting material. These results demonstrate that K2NaAl0.4Ga0.6F6:Mn4+ red phosphor provides a novel choice for the warm WLED required for indoor lighting.

Simultaneous NIR Emission and Thermal Stability Enhancement in Garnet‐Type NIR Phosphors through the Synergistic Effect of Lattice Distortion and Enhanced Rigidity

AbstractEven though there have been significant advancements in the development of Cr3+‐activated near‐infrared (NIR) phosphors, the challenge still remains to develop highly efficient and thermally stable NIR phosphors. Here, the Ca4‐xZnxHfGe3O12:0.03Cr3+ solid solution phosphors with 834–806 nm NIR emission are constructed by substituting Zn2+ for Ca2+, thereby facilitating the formation of [ZnO6] luminescence site. The coexistence of [HfO6] and [Zn/CaO6] luminescence centers is confirmed through DFT calculation, time‐resolved photoluminescence (TRPL) spectroscopy, and low‐temperature‐photoluminescence (77 K) spectroscopy. The formation of [ZnO6] effectively resolves the issue of lattice mismatch between Cr3+ and Ca2+. Furthermore, the simultaneous enhancement of luminescence intensity and thermal stability is realized through a synergistic combination of lattice distortion and rigidity enhancement. By optimizing the substitution concentration of Cr3+, the internal quantum efficiency (IQE) of 92% and an external quantum efficiency (EQE) of 29% are finally achieved. Meanwhile, the thermal stability is also enhanced from 59%@400 K (x = 0) to 81%@400 K (x = 0.8). The developed NIR phosphor‐converted light‐emitting diodes (pc‐LEDs) exhibit promising prospects in the fields of security, biomedicine, non‐destructive testing and rapid identification.

Tailoring Ultra‐Wide Visible‐NIR Luminescence by Ce3+/Cr3+/Yb3+‐alloying Sc‐Based Oxides for Multifunctional Optical Applications

AbstractVisible‐to‐near‐infrared (VIS‐NIR) luminescent materials are in great demand in the field of non‐destructive testing such as component determination and hyperspectral imaging. Although Cr3+‐activated phosphors are widely reported, controllable tailoring ultra‐wide VIS‐NIR luminescence excited by blue light is still a challenge. The strategies of cationic substitution and energy transfers are effective for adjusting the luminescence of Cr3+‐activated phosphors. In this work, a series of Cr3+‐doped Sc‐based solid solution phosphors (Ba3‐mSrmSc4O9:Cr3+) are reported. Under the excitation of blue light, these phosphors exhibit broadband emission due to the different luminescence centers induced by Cr3+ occupying different cationic sites. Because of the weaker crystal field strength, Cr3+ realizes a broadband emission with a longer peak position (λem = 820 nm) and broader full width at half maximum (FWHM≈182 nm) in Ba2SrSc4O9. Furthermore, Ce3+/Yb3+ ions are introduced into Ba2SrSc4O9:Cr3+, achieving an ultra‐wide VIS‐NIR luminescence (460–1200 nm) by the Ce3+→Cr3+→Yb3+ multiple energy transfers. Designing energy transfers is beneficial to improve the quantum efficiency and weaken the thermal quenching. Finally, the NIR phosphor‐converted light‐emitting diode (pc‐LED) fabricated by Ba2SrSc4O9:Cr3+ demonstrates great potential in night‐vision and water component detection. This work provides an effective design idea for controllable tailoring ultra‐wide VIS‐NIR luminescence by chemical substitution and energy transfer.

Optical transition tuning of Er3+ in continuous tungsto-molybdate solid solution NaY(MoxW1-xO4)2 phosphors

Nowadays, the application scenarios of rare earth doped luminescent materials tend to be refined and complicated. The optical properties of rare earth doped materials are difficult to precisely control via the traditional design and synthesis methods, namely, changing doping concentration or preparative conditions. The aim of this study is to tune the optical transition properties of Er3+ in tungsto-molybdate NaY(MoxW1-xO4)2 (x = 0, 0.01, 0.1, 0.3, 0.5, 0.7, 0.9, 0.99 and 1.0) phosphors by changing the host matrix. The Er3+ doped continuous tungsto-molybdate solid solution NaY(MoxW1-xO4)2 phosphors were prepared via a solid state reaction technique at optimized calcination temperatures. The refractive indexes of the obtained solid solution samples were confirmed according to different models and compared. Subsequently, the optical transition intensity parameters, radiative transition rates and intrinsic radiative lifetimes of Er3+ in these solid solution phosphors were calculated in the framework of Judd-Ofelt theory. It was confirmed that the optical transition properties of Er3+ can be greatly tuned by the solid solution composition, and the tuning effects for different transitions are different. To validate the reliability of the Judd-Ofelt calculations, the temperature-dependent emission spectra of two green emissions of Er3+ for different solid solution samples were studied. It was found that the radiative transition rate ratios between two green emissions derived from theoretical calculations and experimental measurements are in reasonable agreement, thus proving that the optical transition calculations are reliable and the optical transition properties of Er3+ in the tungsto-molybdates can be tuned in a large range. This work reminds us of a new route for developing novel luminescence materials based on practical demands.

Long-wavelength near-infrared light emitting Ni2+-doped double perovskite molybdate-based solid-solution phosphors

We developed Ni2+-doped (Sr/Ba)2MgMoO6 double perovskite molybdate-based solid-solution long wavelength near-infrared luminescence (1000–2000 nm) phosphors, which shiftss in the range of 1400–1610 nm by simple adjustment of the Sr/Ba ratio.

From Ancient Blue Pigment to Unconventional NIR Phosphor: A Thermal-Stable Near-Infrared I/II Broadband Emission from Ca1-xSrxCuSi4O10 Solid Solution.

Phosphors used in NIR spectroscopy require broadband emission, high external quantum yield, good ability, as well as a tunable spectral range to meet the detection criteria. Two-dimensional copper silicates MCuSi4O10 (M = Ca, Sr, Ba) play an important part in ancient art and technology as synthetic blue pigments. In the recent years, these compounds were reported to show a broad near-infrared emission when excited in the visible region. Inspired by the tunable structure of MCuSi4O10, a series of broadband phosphors Ca1-xSrxCuSi4O10 were designed for realizing continuously tunable NIR emission by a modulated Cu2+ crystal field environment. The emission maximum exhibits a red shift from 915 to 950 nm and the integral intensity enhances as the Sr2+ content varies in the range of 0-0.50, which is led by the lattice expansion and the following weakened crystal field splitting on tetrahedral-coordinated Cu2+. Compared to CaCuSi4O10, the optimized sample Ca0.5Sr0.5CuSi4O10 shows enhanced NIR emission by about 2.0-fold. It exhibits quite a high external quantum efficiency covering the NIR-I and -II regions (λmax = 950 nm, fwhm = 135 nm, EQE = 26.3%) with a strong absorption efficiency (74.7%) and a long excited-state lifetime (134 μs). These solid-solution phosphors (x = 0.0-0.5) show excellent thermal stability and maintain over 50% of the RT intensity at 200 °C. The optimized phosphor was encapsulated with red-light chips to fabricate NIR pc-LED and put into night-vision application. These good properties make these Cu2+-activated NIR phosphors appealing for multiple applications such as nondestructive testing, night version, lasers, and luminescent solar concentrators.

Crystal Field Engineering Yields New 3D Layered Solid Solution Phosphors (Ca/Sr)4MgAl2Si3O14:Eu2+ for White-Light-Emitting Diode Full-Spectrum Lighting.

The cation-equivalent substitution strategy has the ability to manipulate the luminescence color of phosphors and enhance their overall luminescence performance. A series of novel yellow feldspar-type 3D layered phosphors (Ca1-ySry)4MgAl2Si3O14:xEu2+ were synthesized using a high-temperature solid-state reaction. The solid solution phosphors belong to a tetragonal crystal system with a space group of P4̅21m and cell parameters of a = b = 7.75407-7.91794 Å, c = 5.04299-5.22543 Å, and V = 303.166-327.602 Å3. Under near-ultraviolet (n-UV) excitation, the luminescence color of the phosphor undergoes modulation from yellow-green (530 nm) to blue (467 nm) as the Sr2+ ion substitution ratio increases. This modulation is attributed to the gradual decrease in crystal field splitting energy. Additionally, both the Stokes shift and the full width of the luminescence spectra decrease. Furthermore, there is an increase in the quantum yield (QY) from 45.50 to 60.73%. Finally, the fabricated white-light-emitting diode devices emitted warm white light and achieved high Ra (Ra = 94, 96.6, 92.7) and low correlated color temperature (CCT = 3486, 3430, 3788 K), indicating that the prepared solid solution phosphors can be used as candidate materials for WLED lighting.

High‐Performance NIR Emission in Chromium‐Doped Garnet Phosphors Enabled by Structure and Excitation Regulation

AbstractThe burgeoning phosphor‐converted near‐infrared light‐emitting diodes (pc‐NIR LEDs) have important applications in special illumination and spectroscopy analysis. However, the development of efficient NIR‐emitting phosphors with high performance is still a challenge. In this work, a chemical unit co‐substitution strategy is proposed to realize the excitation transition regulation and successfully achieve high‐performance NIR luminescence in Ca3‐yNayMg1‐ySb2‐xAl2+yO12: xCr3+ (0 ≤ x ≤ 0.05, 0 ≤ y ≤ 1) garnet‐type solid solution phosphors. Through the excitation transition modulation from the 4A2 ground state to the 4T1(4P) and 4T1(4F) excitation state, the excitation intensity at the blue light region is largely enhanced by 25.6 times. Moreover, the NIR‐emitting efficiency and thermal stability are improved, with the optimal luminescence internal quantum efficiency of 90.6% and thermal stability of 97%@423 K, without any flux‐assisted sintering or reduction atmosphere protection. The structure regulation induced small Stokes shift, weak electron‐phonon coupling effect, and decreased non‐radiative transition are responsible for the excellent NIR‐emitting performance. Finally, the NIR pc‐LED is fabricated with photoelectric efficiencies of 18.7%@100 mA and NIR output powers of 63 mW@100 mA, presenting potential applications in nondestructive internal defect detection, veins imaging, and night vision surveillance.

Enhancing External Quantum Efficiency of Blue-Emitting Phosphor Ba(K)-β-Al2O3:Eu2+ by Lattice Site Engineering for Full-Spectrum Lighting.

The discovery of violet-excitable blue-emitting phosphor is a significant breakthrough for the development of phosphor-converted full-spectrum white light-emitting diodes (WLEDs). However, the application of most known violet-excitable blue-emitting phosphors is limited by their low external quantum efficiency (EQE). In this work, we reported on how the EQE values of Eu2+-doped Ba(K)-β-Al2O3 blue-emitting phosphor can be significantly improved through lattice site engineering. By partially substituting K+ for Ba2+, the Eu2+-occupied crystallographic site changes and the coordination polyhedron of Eu2+ shrinks, leading to the increase of crystal field splitting. Consequently, the excitation spectrum exhibits a continuous red shift to match the violet excitation, which enhances the PL intensity of solid solution phosphor (Ba0.4K1.6)0.84Al22O35-α:0.32Eu2+ ((B0.4K1.6)0.84AO:Eu) by 1.42 times compared to that of the end-member Ba1.68Al22O35-α:0.32Eu2+ (B1.68AO:Eu) phosphor. Correspondingly, under the 400 nm violet light excitation, the EQE of optimal blue-emitting (B0.4K1.6)0.84AO:Eu phosphor is up to 53%. Additionally, the phosphor also shows excellent resistance to luminescence thermal quenching (95% at 150 °C). Finally, the WLED fabricated based on (B0.4K1.6)0.84AO:Eu and commercial green and red phosphors exhibited an ultra-high color rending index with Ra = 95.5 and R1-R15 >90. This work offers guidance for tuning the spectral properties of phosphors through lattice site engineering.

Cation substitution induced highly symmetric crystal structure in cyan-green-emitting Ca2La1-xLuxHf2Al3O12:Ce3+ solid-solution phosphors with enhanced photoluminescence emission and thermal stability: Toward full-visible-spectrum white LEDs

Highly efficient cyan-green-emitting phosphors are urgently needed for high-color-quality full-visible-spectrum white light-emitting diodes (LEDs). Herein, we report on efficient near-ultraviolet-excited cyan-green-emitting Ca2La1-xLuxHf2Al3O12:Ce3+ (CLa1-xLuxHA:Ce3+) garnet phosphors, which are developed based on the solid-solution design of chemical cation substitution. All phosphor samples present a garnet crystal structure with the Ia3‾d space group; with increasing Lu3+ ions content, the lattice could be gradually contracted, along with a high symmetry as well as rigidity. Furthermore, under the 408 nm excitation, the cyan-green emissions of CLa1-xLuxHA:Ce3+ phosphors are progressively enhanced with a slight blue-shift, due to crystal field splitting and Stokes shift. Importantly, quantum efficiency and thermal stability performances are greatly improved by introducing smaller Lu3+ ions to replace the bigger La3+ ions, owing to the high rigidity structure with high symmetry. The optimized CLa0.5Lu0.5HA:Ce3+ phosphor exhibits an intense cyan-green emission band with high internal quantum efficiency of 76.4% and external quantum efficiency of 54.4%. Through employing the as-prepared CLa0.5Lu0.5HA:Ce3+ cyan-green phosphor, we have successfully fabricated a full-visible-spectrum LED device, demonstrating a bright warm-white light emission with an extremely high color rendering index (Ra = 98.0, R9 = 95.9, and R12 = 94.3) and low correlated color temperature (3497 K) under 100 mA driving current. This study not only reveals the correlation between the crystal structure evolution and luminescent properties of phosphor materials, but also provides new strategies for the design and development of novel efficient luminescent materials for high-quality full-visible-spectrum LED lighting.

Highly efficient near-infrared solid solution phosphors with excellent thermal stability and tunable spectra for pc-LED light sources toward NIR spectroscopy applications.

Near-infrared (NIR) luminescent materials have attracted wide research interest due to their unique photophysical properties for designing NIR light-emitting diodes (NIR LEDs). Here, a series of Cr3+-activated NIR-emitting solid solution phosphors, Gd1-xLux(Al1-xScx)3(BO3)4:0.01Cr3+ (GLASB:Cr3+) (x = 0 to 0.5), are successfully synthesized via a cosubstitution approach. The GLASB:Cr3+ phosphors reveal extraordinary optical performance with a desirable high IQE of 93.6%, considerable broadened FWHM (from 128 nm to 196 nm) and redshift of 119 nm (747 → 866 nm) as the amount of [Lu3+-Sc3+] ion doping increases. Moreover, their photoluminescent thermal stability is substantially improved, maintaining 105.7% of the initial integral intensity up to 150 °C, namely zero-thermal-quenching. The NIR pc-LED fabricated using the GLASB:Cr3+ phosphor generates an NIR output power of 46 mW and an electro-optical efficiency of 37% at a 120 mA input current. Finally, the characteristic NIR emission of this phosphor can not only be utilized in the fields of night-vision technology and biometric identification, but also exhibits a perfect match with the absorption of the bacteriochlorophyll (BChl) and light-harvesting protein (LHP) of photosynthetic bacteria (PSB), presenting a high application prospect for improving PSB photosynthesis.

Extending the optical temperature sensing range of Cr3+ by synchronously tuning 2E and 4T2 emission.

Due to the different sensitivities of the 2E and 4T2 energy levels of Cr3+ to the local environment, Cr3+-doped fluorescent materials appear as excellent candidates for highly sensitive temperature sensing based on luminescence intensity ratio technology. However, a way to broaden the strict Boltzmann temperature measuring range is rarely reported. In this work, through Al3+ alloying strategy, a series of SrGa12-xAlxO19:0.5%Cr3+(x = 0, 2, 4, and 6) solid-solution phosphors were synthesized. Remarkably, the introduction of Al3+ can play a role in regulating the crystal field around Cr3+ and the symmetry of [Ga/AlO6] octahedron, realizing the synchronous tuning of 2E and 4T2 energy levels when the temperature changes in a wide range, achieving the purpose of increasing the intensity difference of 2E → 4A2 and 4T2 → 4A2 transitions, so as to extend the temperature sensing range. Among all samples, SrGa6Al6O19:0.5%Cr3+ showed the widest temperature measuring range from 130 K to 423 K with Sa of 0.0066 K-1 and Sr of 1% K-1@130 K. This work proposed a feasible way to extend the temperature sensing range for transition metal-doped LIR-mode thermometers.

Super Broadband Near‐Infrared Solid Solution Phosphors with Adjustable Peak Wavelengths from 1165 to 875 nm for NIR Spectroscopy Applications

AbstractCr3+‐activated near‐infrared (NIR) phosphors have attracted wide attention owing to applications in phosphor‐converted light‐emitting diodes (pc‐LED) for spectroscopy. Because a broader spectrum covers more information to detect, the width of the spectrum is an important parameter to consider. Here, the blue LED excitable ultra‐broadband Cr3+‐activated LiInGeO4 phosphors, which exhibit unprecedented long‐wavelength NIR emission with a wide full‐width at half maximum (FWHM) of 305 nm, are developed. The overall emission tuning from 1165 to 875 nm with broadened FWHM from 305 to 508 nm is realized through designing continuous solid solution hosts of LiIn1−zSczGeO4/(LiIn)1−yMg2yGeO4 and finite solid solution hosts of (LiIn)1−yZn2yGeO4:Cr3+. The observation of such long‐wavelength NIR from Cr3+ not Cr4+ is studied and confirmed by electron paramagnetic resonance, X‐ray absorption near‐edge structure, and steady‐/transient‐state photoluminescence. The formation of finite solid solutions induces the change in the local structure of Cr3+ that ultimately leads to the observation of super broadband (FWHM = 508 nm) luminescence. The luminescence mechanism is discussed in this study. Finally, this study demonstrates that the as‐synthesized phosphors with tunable NIR luminescence can be well used in NIR pc‐LEDs for spectroscopy detection.

Luminescent thermal behavior of Eu3+ in K5Bi(MoxW1-xO4)4 phosphors

From the practical point of view, the luminescent thermal behavior of phosphors is an important factor. In this work, two factors are found to influence the thermal quenching behavior of Eu3+ in a series of Eu3+ doped K5Bi(MoxW1-xO4)4 solid solution phosphors. These factors are the energy of the charge transfer state (CTS) and the thermal ionization process. With the introduction of Mo in the host matrix, the energy of CTS decreases, and the thermal ionization process is enhanced, which leads to a deterioration of thermal stability in solid solution phosphors. The thermal stability is improved by increasing the doping content of Eu3+, which may correlate to the weakening of the thermal ionization process. The K5Bi0.7(Mo0.5W0.5O4)4:0.3Eu phosphor possesses favorable color stability and color purity at high temperatures. Meanwhile, such phosphor matches well with a 365 nm LED chip and exhibits intense and pure red emission at a drive current of 200 mA.

Enhanced cyan emission via competitive site occupancy engineering in Sr2SiO4:Eu2+ phosphor for achieving full-spectrum LED lighting

Highly efficient containing cyan-emitting phosphors are used to bridge the cyan cavity for near ultraviolet (NUV) light-emitting diodes (LEDs) to obtain high-quality full-spectrum white lighting. In this work, a series of Sr2-xNaxSi1-xNbxO4:Eu2+ (x = 0–0.25) (SNSNO:Eu2+) solid solution phosphors were prepared by a solid-state reaction method. The bright SNSNO:Eu2+ phosphors were proceeded to fill the cyan gap. Such a cosubstitution of Na + -Nb5+ ion pair improves the cyan sub-band emission peaking at around 500 nm owing to the competitive site occupancy of Eu2+ on the Sr2+ site. Notably, codoping Na+-Nb5+ ion pairs into the host can realize a tuning of spectrum of SNSNO:Eu2+ from yellow-green to cyan-green region by crystallographic site engineering. Finally, employing mixture of SNSNO:Eu2+ and commercial BAM:Eu2+ and CaAlSiN3:Eu2+ coated on a 365 nm NUV chip, a full spectrum wLED package with remarkable color rendering index (Ra = 95.1) and low CCT = 3167 K was generated. The results indicate that the SNSNO:Eu2+ phosphor is very significative on closing the cyan gap for full-spectrum white lighting.

Energy transfer, colour tuneable emissions and LED application of solid solution phosphors K2Y1-x-yTbxEuyZr(PO4)3

Development of multi-colour emitting phosphors for applications in LED is always a hot topic in rencent years. Herein, we prepared solid solutions K2Y1-x-yTbxEuyZr(PO4)3 and studied their luminescent properties. Both Tb3+ and Eu3+ emission peaks can be generated by using characteristic exciting wavelength of Tb3+ (378 nm) due to the Tb3+→Eu3+ energy transfer. By simply changing the relative proportions of Tb3+/Eu3+, the emitting color of phosphors K2Tb1-yEuyZr(PO4)3 changes from green (y = 0), through yellow (y = 0.005) to red (y = 0.08). Thermostability study showed that at 150 °C, the integral intensity is 57% of that at 25 °C, suggesting a good thermostability. Finally, we fabricated three LED lamps by using a 365 nm chip with y = 0, 0.005, 0.08 phosphors, and green, yellow and red light can be observed.

Achieving opto-responsive multimode luminescence in Zn1+xGa2−2xGexO4:Mn persistent phosphors for advanced anti-counterfeiting and information encryption

Optical characteristics of phosphors, e.g. color output, decay process and external field stimulation mode (including opto-, thermo- and mechano-stimulation), play an important role in the areas of information storage, anti-counterfeiting and bio-imaging applications. Persistent luminescence (PersL) phosphors are particularly suitable for such applications owing to their multimodal luminescence features such as photoluminescence (PL), PersL, photostimulated luminescence and mechanoluminescence. However, conventional PersL phosphors are suffering from a huge challenge to develop a single material for multicolor anti-counterfeiting. Herein, the Zn1+xGa2−2xGexO4:Mn (0 ≤ x ≤ 1) solid solution phosphors are synthesized, which can emit from green to yellow, golden, pink, and red PL. In addition, the phosphors also show the thermo-mechano-opto-stimulated green PersL after irradiation of a UV 254/365 nm lamp. Based on the multimode and multicolor luminescence features, the advanced anti-counterfeiting and optical data storage are designed. Results show that the multimodal luminescence feature with high information capacity can be conveniently identified by using a luggable ultraviolet lamp or NIR laser diode. This extraordinary material will make anti-counterfeiting more sophisticated and show advanced security in the applications of data encryption.