Color-tunable Phosphors Research Articles

Tunable Luminescence of Sm3+/Tb3+ Co-Doped CaMoO4 Phosphors Synthesized by Microwave-Assisted Heating

We present a series of Sm3+/Tb3+ co-doped CaMoO4 phosphors synthesized by an efficient method of microwave-assisted heating. The prepared CaMoO4 samples were characterized by X-ray diffraction, photoluminescence, and Commission Internationale de l’Elcairage (CIE) chromaticity diagram. The X-ray diffraction results confirmed that all synthesized CaMoO4 samples are crystallized in a pure tetragonal phase. The photoluminescence spectra significantly show both red- and green emissions in the synthesized Sm3+/Tb3+ co-doped CaMoO4 phosphors. It is obvious that the variations in the intensity ratio of red/green emissions depend on the molar ratio of Sm3+/Tb3+ co-doping and dominate the CIE color coordinates on the chromaticity diagram. The investigations showed the functionality of the material system as advanced color-tunable phosphors for white-LEDs as evidenced by the controllability of the light-emitting region of Sm3+/Tb3+ co-doped CaMoO4 phosphors through the adjustment of the molar ratio of Sm3+/Tb3+ ions.

Energy transfer from Tb3+ to Eu3+ in LiSrY2(BO3)3: Candidates for UV or NUV excited color tunable phosphors

Tb3+ is a typical green-emitting activator and in some cases could sensitize Eu3+ through energy transfer, leading to color tunable emissions by changing their relative contents. In this work, Tb3+ and Tb3+/Eu3+ were singly- and co-doped into the borate host LiSrY2(BO3)3 with the formulas LiSr(Y1-xTbx)2(BO3)3 (0 <x ​≤ ​1) and LiSr(Y0.7-yTb0.3Euy)2(BO3)3 (0.001 ≤ y ​≤ ​0.03). Powder XRD confirms the phase purity by extracting the cell lattice parameters, which exhibit a linear dependence on doping contents. Due to the local symmetry-broken characteristic of the rare earth cation in this host, relatively strong f-f excitations in the NUV range were observed for Tb3+-phosphors, and concentration quenching effect was observed at x ​= ​0.30 and 0.50 when excited by 260 and 365 ​nm, respectively. As expected, the Tb3+ to Eu3+ energy transfer was confirmed, thus was utilized to color tunable emissions from green to red.

Structure and luminescence properties of color-tunable phosphor Sr2La3(SiO4)3F:Tb3+,Sm3+

A series of single-phase and color-tunable phosphors Sr2La3(SiO4)3F:0.15Tb3+,xSm3+ (SLSOF:0.15Tb3+,xSm3+) was prepared using solid-state route. The X-ray diffraction (XRD) was used to characterize the phase of the as-prepared samples. The synthesized phosphors have apatite-type structure without other impurities. Sm3+ and Tb3+ ions substitute La3+ into the lattice and form a single-phase solid solution. The elements are evenly distributed in the sample according to the scanning electron microscopy (SEM) results. The crystal structure of the host phosphor was refined by the Rietveld method. The optical properties were studied in detail by investigation of the luminescence and diffuse spectra, fluorescence decay curves and energy transfer efficiency. The phosphor color can be changed from green (0.29, 0.48) to yellow/orange and red (0.57, 0.42) via adjusting the doping ratio of Sm3+. The SLSOF:0.15Tb3+,xSm3+ phosphors can emit typical multicolor light such as green, yellow, orange and red with gradually increasing Sm3+ doping concentration. All results indicate the occurrence of the energy transfer which results in the color-tunable properties of the phosphors.

Activators lattice migration strategy customized for tunable luminescence of Ce3+ doped β-Ca3(PO4)2

The luminescent properties of phosphors are determined by the electronic configuration of their activators and the crystal environment in which they are embedded. By manipulating the site-selective occupancy of activators, we can coordinately control the local crystal field and electron cloud distribution to master the movement of emission wavelength and obtain a color-tunable phosphor. The system of β-Ca3(PO4)2 is an excellent carrier for crystal-site engineering to modify luminescent performance. It has five distinct crystal sites and a strong photoluminescence response. However, due to low doping concentration and structural complexity, the specific occupation of Ce remains unknown. We discussed the specific position of Ce in this study and proposed a novel activators lattice migration strategy for controlling the relative strength of crystal field splitting (CFS) and the nephelauxetic effect (NE) to control luminescence properties. By combining X-ray Absorption Fine Structure (XAFS) with DFT calculation, we predicted the local environment of each crystal lattice and migrated Ce3+ from M(3) to a strengthened crystal field site with a lower coordination number, shorter bonding bond length, and greater polyhedral distortion, M(5), resulting in phosphors with tunable luminescence emission. Relevant parameters ΔD(Ce3+) were identified for dealing with interference caused by the electronegativity difference during a structural modification. Some potential applications emerged as a supplement and an intriguing QR-code and response program for epidemic prevention were demonstrated. This structure–activity relationship-based strategy provides new inspiration for designing luminescent materials with tunable emission and a broader range of applications.

Harvesting Light from BaHfO3/Eu3+ through Ultraviolet, X-ray, and Heat Stimulation: An Optically Multifunctional Perovskite.

Materials with optical multifunctionality such as photoluminescence (PL), radioluminescence, and thermoluminescence (TL) are a boon for a sustainable society. BaHfO3 (barium hafnium oxide [BHO]) under UV irradiation demonstrated visible PL endowed by oxygen vacancies (OVs). Eu3+ doping in BHO (BHOE) introduces f-state impurity levels just below the conduction band for both Eu@Ba and Eu@Hf sites, causing efficient host-to-dopant energy transfer, generating intense 5D0 → 7F1 magnetic dipole transitions (MDT) with internal quantum yield of ∼70%. X-ray photoelectron spectroscopy and electron paramagnetic resonance showed the formation of OVs in both BHO and BHOE samples with more vacancies in the doped sample. The positron lifetime measurements suggested that Eu3+ ions are distributed at both Ba2+ and Hf4+ sites. The association of OVs with Hf4+ and Eu3+ ions due to high charge/radius ratio is considered to be responsible for lowering the symmetry around Eu3+ ions to C4v in BHOE. Density functional theory studies of defect formation energy justified the same. Time-resolved emission spectroscopy showed distinct spectra for Eu@Ba and Eu@Hf sites corresponding to symmetric and asymmetric environments, respectively. This could be highly relevant in designing color tunable phosphor by forcing dopant ions at one specific site because Eu@Ba displayed orange emission whereas Eu@Hf displayed red emission. We could further harness BHOE for X-ray scintillator application by designing a thin film, which showed efficient conversion of high-energy X-ray into visible light. Under beta irradiation; both BHO and BHOE showed distinct TL glow curves as shallow traps were formed in the former and deep traps in the latter, which could have long-term implications in harnessing this material for persistent luminescence. We believe that BHO/BHOE demonstrated an extraordinary credential as a perovskite for multifunctional applications in the area of defect-induced light emission, UV phosphor, X-ray scintillator, and TL crystals.

Self-calibrated ratiometric thermometers and multi-mode anti-counterfeiting based on Ca2LaNbO6:Pr3+ optical material

Optical materials have been extensively used in thermometers and anti-countering for their non-contact, advantageous rapid, and high precision properties. Herein, a double-perovskite Ca2LaNbO6:Pr3+ color-tunable phosphor was synthesized. The emissions (blue, green, red1, and red2) from Ca2LaNbO6:Pr3+ phosphor have different temperature-dependent properties because of the thermal quenching channel generated by the intervalence charge transfer state between Pr3+ and Nb5+ ions. They can be used to realize four fluorescence intensity ratio models (Green/Blue, Green/Red2, Red1/Blue and Red1/Red2) to measure temperature with high absolute and relative sensitivities. Moreover, using the Ca2LaNbO6:Pr3+ phosphor and the carbon dots with green afterglow to create anti-counterfeiting patterns, the multi-mode anti-counterfeiting under different portable lamps (254 nm and 365 nm) was realized. Therefore, the prepared multifunctional phosphor indicated a potential application in both optical temperature sensing and anti-counterfeiting simultaneously.

Energy Transfer from Tb3+ to Eu3+ in Lisry2(Bo3)3: Candidates for Uv or Nuv Excited Color Tunable Phosphors

Energy Transfer from Tb3+ to Eu3+ in Lisry2(Bo3)3: Candidates for Uv or Nuv Excited Color Tunable Phosphors

Luminescence properties of color-tunable phosphor material CaF2: Eu

Controlled luminescence tuning can modify the luminescence performances of fluorescent materials. A series of color tunable Eu doped CaF2 samples were prepared by the high-temperature solid-state reaction method under different reducing atmospheres. The powder X-ray diffraction, emission spectra, excitation spectra and decay curves were collected to characterize the samples. It is proved by the X-ray diffraction data the samples maintain the cubic fluorite structure without other new phases. PL results show that Eu3+ and Eu2+ ions coexist in the host material when the sintering has been carried out in a partially reducing atmosphere. The samples under such sintering conditions exhibits tunable-color properties by changing the doping concentration. Additionally, the CIE chromaticity coordinates of these CaF2: Eu samples greatly depend on the excitation wavelength. Warm white-light emission has been observed in the sample of CaF2: 0.5% mol Eu when the excitation wavelength is around 319 nm. These results indicate that these CaF2: Eu samples have potential to be used in the field of LEDs.

Luminescence and energy transfer of color-tunable Tb3+/Sm3+co-doped BaZn2(PO4)2 glass-ceramic phosphors

The color-tunable phosphors can be obtained by co-doping strategy and energy transfer regulation. In this work, Tb3+ and Sm3+ co-doped BaZn2(PO4)2 glass-ceramic (GC) phosphors are prepared and their structural, optical and luminescent properties are characterized. By adjusting the doping concentration of Sm3+, The luminescent color of BaZn2(PO4)2 GC: Tb3+/Sm3+ Phosphors ranges from green to light green to yellow-green and finally to yellow. The photoluminescence (PL) spectra and fluorescence decay curves confirmed the energy transfer from Tb3+ to Sm3+, and the energy transfer efficiency (η) increased monotonically with the increase of Sm3+ concentration. Moreover, the energy transfer mechanism from Tb3+ to Sm3+ in BaZn2(PO4)2 GC is a dipole-dipole interaction. The typical BaZn2(PO4)2 GC: 0.75 Tb3+/0.75Sm3+ phosphor has a high thermal stability with an activation energy determined to be 0.29525 eV. Coupling BaZn2(PO4)2 GC: 0.75 Tb3+/0.75Sm3+ Phosphors with commercially available ultraviolet light-emitting diodes (UV-LEDs) chips yields luminescent color coordinates of (0.3965, 0.4253) and a color correlation temperature of 3927 K, close to warm white light emission. These results indicated that the Tb3+ and Sm3+ co-doped BaZn2(PO4)2 GC achieved luminescence color modulation, which has potential applications in UV-converted LEDs and other optical devices.

Controllable Synthesis and Luminescence Properties of Zn2GeO4 : Mn2+ Nanorod Phosphors

AbstractIn this study, color tunable phosphors (Mn2+‐doped Zn2GeO4) were successfully synthesized by a facile microwave hydrothermal process with H2O as solvent. Crystal field modulation and band gap doping by Mn2+ substitution for Zn2+ realizes color tunable Mn2+ emission from 424 to 535 nm. Mn2+‐doping on the phase and size transition of Zn2GeO4 nanocrystals was discussed, and a possible Zn2GeO4 : xMn crystal growth mechanism is discussed. Photoluminescence (PL) spectra indicate that the d‐d transition of manganese ions (4T1→6A1) corresponds to a strong green emission of Zn2GeO4 : xMn phosphors.

High pressure induced disappearing 5D0 → 7F2 and broadening 5D0 → 7F1 transitions from Y2Hf2O7:Eu3+ nanoparticles

Design of color tunable phosphors as pressure sensors has drawn immense attention. In this work, luminescent Y2Hf2O7:Eu3+ nanoparticles upon high pressure demonstrate lowered phonon frequency, enhanced crystal field, and increased local site swapping effect as manifested with appearing emission of 5D1/5D2 levels, increasing width of magnetic dipole transition (up to ~11.43 GPa), and increased symmetry around Eu3+ ion with disappeared 5D0 → 7F2 transition beyond 5.7 GPa. Our results indicate the potential of the Y2Hf2O7:Eu3+ nanoparticles as medium range pressure sensors with tunable luminescence from red to orange to yellow in the pressure range of 0–49.4 GPa.

Li2O–Al2O3–ZnO–P2O5:Dy3+/Sm3+/Eu3+ glasses for solid-state yellow laser and color tunable phosphor applications

Li2O–Al2O3–ZnO–P2O5:Dy3+/Sm3+/Eu3+ glasses for solid-state yellow laser and color tunable phosphor applications

Tunable light emission from single phased Ba2CaZn2Si6O17:Pb2+, Eu3+ silicate phosphors via energy transfer efficiency for white light emitting diode applications

In this work, the non-rare earth element Pb2+ ions doped, and co-doped with the rare earth element Eu3+ ions in the silicate based Ba2CaZn2Si6O17 phosphors were prepared by using the simple solid state reaction process. To know about the phase formation, and the surface morphology of the as prepared powder samples, the powder X-ray diffraction (PXRD), and the scanning electron microscope (SEM) techniques were employed respectively. To measure the luminescence properties of the phosphors, the photoluminescence excitation (PLE), and the photoluminescence (PL) emission were recorded. Under the 293 nm excitation, the co-doped phosphors (hereafter referred to as phosphors/samples) exhibit ‘a broad blue emission band at 438 nm’, and ‘five sharp bands at 579, 593, 611, 653, and 704 nm’, corresponding to the characteristic transitions of the Pb2+ and the Eu3+ ions in the same order. The energy transfer efficiency in the phosphors, between the sensitizer Pb2+, and the activator Eu3+ ions, was investigated. The effect of the concentration quenching is used to calculate the critical distance Rc in the sample was obtained to be 16.74 Å. The PL decay time showed a decreasing trend when the concentration of the Eu3+ activator ions was increasing. The PL emission spectra of the samples were used to measure the CIE chromaticity color coordinates, and the correlated color temperature (CCT). The quantum efficiency values of the samples were also measured. Finally, to know about the PL thermal stability of the phosphor, the temperature dependent photoluminescence (TDPL) was performed, and the activation energy was calculated as 0.167 eV. From the above results, the Ba2CaZn2Si6O17:Pb2+, Eu3+ phosphors can be the promising color tunable phosphors in the white light emitting diode (WLED) applications.

Luminescence properties and energy transfer of color-tunable LaAl2.03B4O10.54:Tm3+,Dy3+ phosphors

LaAl2.03B4O10.54:Tm3+,Dy3+ phosphors were prepared by the sol–gel method. The phase, luminescence properties, energy transfer mechanism and CIE color coordinates of the samples were analyzed by XRD, SEM and fluorescence spectrometry. The results show that the LaAl2.03B4O10.54:Tm3+ phosphor emits blue light at a monitored wavelength of 357 nm and the concentration quenching point of Tm3+ ion is 0.06 mol. In the La0.94-yAl2.03B4O10.54:0.06Tm3+,yDy3+ phosphors, the luminescence intensity of Tm3+ decreases with an increase in the Dy3+ doping concentration, while the luminescence intensity of Dy3+ increases. The color of the emitted light can be adjusted by changing the doping concentration of Dy3+ or changing the wavelength of the excited light. There is energy transfer between the Tm3+ and Dy3+ ions. When the doping concentration of Dy3+ ions is 0.1 mol, the energy transfer efficiency reaches 63.65% and the energy transfer mechanism is an electric dipole-electric dipole interaction. These results clearly indicate that La0.94-yAl2.03B4O10.54:0.06Tm3+,yDy3+ phosphors can be used as color tunable phosphors in the field of WLEDs.

Luminescence and Energy Transfer of Li2Y4(MoO4)7: Ln3+ (Ln = Dy, Eu) Phosphors

A series of novel Li2Y4(MoO4)7: Ln3+ (Ln = Dy, Eu) phosphors with color-tunable were prepared through solid-state reaction. The crystal structures, photoluminescence properties, energy transfer process, decay, and chromaticity coordinates were also investigated. The emission color of Li2Y4(MoO4)7: Ln3+ (Ln = Dy, Eu) phosphors were tunable from pale yellow to the nearly white position by adjusting the concentrations of Dy3+ and Eu3+ ions or converting the excitation wavelength from 353 nm to 391 nm, and η τ could reach 49.33% when y = 0.60. These results indicated that Li2Y4(MoO4)7: Ln3+ (Ln = Dy, Eu) may be served as color tunable phosphors.

Critical review on lanthanide activated LED phosphors

Broad range of phosphors has been utilized for LEDs in past few years, subsequently, encourages the phosphor-converted LEDs (pc-LEDs). Proposed article gives an idea about the different color tunable phosphors used in solid state lighting. Different properties of different color emitting phosphors have been done with the mixing of rare earths in the host lattice of luminescent centered materials which shows color emission in the visible range. There is a concise approach toward the different characteristics and records related with the color quality and execution of pc-LEDs. So this article mainly deals with role lanthanides in LED phosphors and their characteristics in the field of luminescence.

Rare Earth (RE) doped color tunable phosphors for white light emitting diodes

Currently, white light-emitting diodes (WLEDs) are emerging lighting techniques and are highly desirable. These are one of the world’s highest lighting technologies. LEDs have attracted special attention of research society, scholars and society through their benefits and applications. Phosphor-converting light-emitting diodes (PC-LEDs) show immense potential for the future and, in the coming years, it is expected that LEDs will be easily available at a cheaper price with lower energy consumption. Rare earth activated phosphors are an integral and important part of white light generation. In this review, we have studied numerous research papers about phosphor-converted light-emitting diodes (pc-LED). The main objective of this review paper is to analyze inorganic materials that have been synthesized by various methods and are suitable for eco-friendly lighting applications. In this review, we propose the plan and discovery of new LED phosphors from two alternate points of view, i.e., basic crystal structure in various host systems and co-doped activators through energy transfer. The color-tunable properties of rare-earth activated phosphors explain in detail. Numerous color-tunable phosphor materials have been studied and discussed in this review. In addition, utilizations, difficulties and development or improvement of pc-WLEDs will be discussed.

Current progress and comparative study of performance of the energy saving lighting devices: a review

In the present scenario, rare earth activated phosphor materials are important families in luminescent materials, which is useful in various applications. Over the past few years, rare earth activated phosphor has gained a lot of attention from the society and research community due to its exceptional properties such as low cost, eco-friendly behavior, solution process ability, better PL properties, wider range of color tunability, color purity and defects tolerance etc. In this review, we first discuss energy saving lighting devices, after that, we have discussed those methods which are used to synthesize rare earth activated phosphors. We have been focusing on the modification and tailoring of the photoluminescence of phosphors, which may lead to the acquisition of new phosphors with tunable emission colors. In this review, we are discussed recently reported color tunable phosphors. At the end of the review, scope in lighting field, energy saving devices, and future scope also discussed.

Luminescence and Energy Transfer of Color-Tunable Y2Mg2Al2Si2O12:Eu2+,Ce3+ Phosphors.

Color-tunable phosphors can be obtained through codoping strategies and energy transfer regulation. Ce3+ and Eu2+ are the most common and effective activator ions used in phosphor materials. However, the energy transfer from Eu2+ to Ce3+ is rarely reported. In this work, Y2Mg2Al2Si2O12(YMAS):Eu2+,Ce3+ phosphors were successfully synthesized, which was confirmed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Rietveld refinement, scanning electron microscopy (SEM) and element mapping images, and spectral information. The luminescent color of YMAS:Eu2+,Ce3+ phosphors could be tuned from blue to cyan to light green to yellow-green and finally to green-yellow, which was achieved by adjusting the energy transfer between different dopants. The energy transfer from Eu2+ to Ce3+ was confirmed by photoluminescence spectra and fluorescence decay curves. Within the experimental gradient, the energy transfer efficiency could reach up to 48%. At 373 K, the Y1.99Mg1.99Al2Si2O12:0.01Eu2+,0.01Ce3+ (YMAS:0.01Eu2+,0.01Ce3+) phosphor exhibited a total integral emission loss of only 8%, and the emission peak intensity decreased to 95%, indicating the excellent thermal stability. The white light-emitting diode (WLED) fabricated by the YMAS:0.01Eu2+,0.01Ce3+ phosphor has the same level correlated color temperature (CCT = 5841 K), greatly improved color rendering index (Ra = 87.8), and higher quality white light color (CIE = (0.3258, 0.3214)) than the WLED made by the YMAS:0.01Eu2+ phosphor, indicating that the performance of the phosphor was significantly improved by introducing Ce3+. This work provides an effective guide for the design and development of highly efficient color-tunable phosphors involving energy transfer from Eu2+ to Ce3+ in some specific materials, such as garnet structures.

Energy transfer and the anti-thermal quenching behavior of Sr8MgCe(PO4)7:Tb3+ for temperature sensing

Novel color-adjustable phosphors Sr8MgCe(PO4)7:Tb3+ were synthesized by the solid-state reaction method. The X-ray diffraction was used to characterize the phase formation. The host shows blue emission under 310 nm excitation, ascribed to the 5d-4f transitions of Ce3+, while Sr8MgCe(PO4)7:xTb3+ phosphors exhibit the emission band of Ce3+ as well as the characteristic lines of Tb3+ under 310 nm excitation. The color variation was observed as the concentration of Tb3+ changes. Moreover, the host sensitizes the emission of Tb3+ through the energy transfer process, and the mechanism is the dipole–dipole interaction. In addition, the emission of the host declines with the increase of the temperature while that of Tb3+ increases. This anti-thermal quenching behavior was interpreted by the configurational coordinate diagram. In addition, the temperature sensing behavior based on the emission peaks of the host and Tb was studied in the range 298–523 K, and the largest sensitivity is 0.379% K−1. The results indicate that Sr8MgCe(PO4)7:Tb3+ is an attractive color-tunable phosphor for solid state lighting and temperature sensing.