As-synthesized 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.

Photoluminescence properties of Mn2+-activated red-emitting phosphors with superior thermal stability for backlighting display applications

The red-emitting phosphors, Na2Mg1-x(PO3)4:xMn2+ with concentrations ranging from 0.01 to 0.11, have been successfully synthesized using a simple solid-state method. The as-synthesized phosphors are crystallized in an orthorhombic structure. The luminescence mechanism of Mn2+ ions in Na2Mg(PO3)4 lattice has been deeply explained using the Tanabe-Sugano (T-S) energy level diagram for the d5 electron configuration. The typical photoluminescent emission (PL) and photoluminescent excitation (PLE) spectra were measured. Several excitation peaks in the spectral range of 250–550 nm on the PLE spectrum and a strong emission peak at 613 nm indicate that the as-synthesized phosphors can be effectively excited using ultraviolet (UV) and near-UV LED chips. Several photometric characteristics were measured, such as the Commission International de'LEclarirage (CIE) chromaticity coordinate (x, y), color purity (CP), and correlated color temperature (CCT), corresponding to the concentration-dependent PL spectra. Furthermore, the thermal stability of the Na2Mg1-x(PO3)4:xMn2+ phosphors was investigated through temperature-dependent PL spectra and decay curves from 10 to 500 K. All results confirm that the as-synthesized red-emitting phosphors exhibit excellent thermal stability, which are attractive characteristics for white light emitting diodes (W-LEDs) applications.

Dy3+ doped KCa(PO3)3 phosphor for white light generation: structural and luminescent studies

Using the traditional solid-state reaction approach, Dy3+ ions doped KCa(PO3)3 phosphors have been synthesized to investigate their luminescent properties to produce high-quality white light for solid-state lighting applications, particularly in white LEDs. x-ray diffraction (XRD) patterns were used to examine the structure and phase of the phosphors. Using scanning electron microscopy (SEM), the morphology of the as-synthesized phosphor has been investigated. Fourier transform infrared spectroscopy (FT-IR) has been used to investigate several vibrational bands seen in the phosphor. Using diffuse reflectance spectra (DRS), the as-synthesized phosphors’ optical band gap values have been estimated. When Dy3+ ions are excited at 350 nm, the photoluminescence (PL) spectra characteristics observed for the activated KCa(PO3)3 phosphor show strong white area emission due to both 575 nm, which is related to the 4F9/2 → 6H13/2 and 482 nm that is ascribed to 4F9/2 → 6H15/2 transition of Dy3+ ions. Additionally, the concentration quenching of Dy3+ ions doped at 4 mol% is seen in the PL spectra. Based on the observed PL spectra, the computed CIE chromaticity coordinates for the optimised KCa(PO3)3 phosphors are located in the deep white area. The lifespan of the as-titled phosphors decreases as the amount of Dy3+ ions increases in the host lattice. Additionally, the PL decay profiles shows a dual exponential behaviour when excited at 350 nm, with an emission wavelength at 575 nm. The lifetime values were used to calculate the quantum efficiency of the as prepared phosphors. On the basis of the results of the aforementioned studies, we wish to project Dy3+ ion doped KCa(PO3)3 phosphors as white light generating materials in w-LEDs and for other photonic applications.

A competitive trivalent-europium-activated phosphor: Achieving highly efficient red light emission in a sodium-rich garnet host

The reaction temperature is key factor for light-emitting phosphors synthesized by solid state method because it directly determines the crystallinity and further affects the luminescence property of the phosphors. While high temperature certainly benefits to the solid diffusion in reaction, it would waste enormous energy during long time heating. Herein, a novel Eu3+-activated and highly efficient red phosphor, NaGd2Ga3Ge2O12:Eu3+, is reported. By the reconstruction of the traditional Y3Al5O12 garnet host into the sodium-rich NaGd2Ga3Ge2O12 one, huge decrease of the synthesis temperature is successfully achieved. More importantly, such decrease of the synthesis temperature does not dissatisfy the luminescence property of the NaGd2Ga3Ge2O12:Eu3+ phosphors. Instead, the Eu3+ in the NaGd2Ga3Ge2O12 exhibits extremely high quantum yield up to 96.78% upon 394 nm excitation, showing great competitiveness among other iso-structral garnet hosts. This work indicates that the introduction of sodium in the eight-coordinated rare earth site of the garnet host can not only reduce the energy consumption during the stage of phosphor synthesis but also avoid the loss of excitation energy during the light converting stage of the Eu3+ to a large extent. By fabricating the as-synthesized red phosphor into a near-UV chip together with commercial green and blue phosphors, quality white light-emitting diodes with satisfactory color rendering index (as high as 90) and correlated color temperature (as low as 3986 K) can be easily obtained.

Synthesis, Structural and Fluorescence Investigations of Novel Li2Ba5W3O15:Sm3+ Phosphors for Photonic Device Applications.

In the current study, Sm3+ ions doped Lithium Barium Tungstate (Li2Ba5W3O15) (LBW) phosphors with the ability to emit orange-red light were made using the traditional high-temperature solid-state reaction technique. The structure and phase of the as-synthesized phosphor samples were examined via X-ray diffraction (XRD) patterns. The diffraction peaks of the undoped LBW and Sm3+ ions doped LBW phosphors closely resemble those of the Joint Committee on Powder Diffraction Standards (JCPDS) pattern with card number 01-072-1717. Scanning electron microscopy (SEM) was employed for the analysis of the morphological characteristics of the synthesized phosphor material. Fourier Transform Infrared (FT-IR) spectroscopy was used to study several vibrational and molecular bands present in the host matrix. Using diffuse reflectance spectra (DRS), the optical band gap values (Eg) were evaluated by applying Tauc's method. The photoluminescence (PL) spectra characteristics at λex = 336nm indicate the emission of dopant ions (Sm3+) in the deep orange-red region corresponding to 4G5/2 → 6H5/2 transition (at 581nm) with concentration quenching after 2mol % of Sm3+ ions. Using the PL spectra, the CIE chromaticity coordinates of LBWS2.0 phosphor were estimated and found in the deep visible orange-redarea, indicating the potential use of the prepared phosphor material for phosphor-converted white light emitting diodes (w-LEDs) applications. Double exponential behaviour can be seen in the PL decay spectralprofiles obtained under λem = 581nm and λex = 336nm. The experimental lifetimes (τexp) decrease as the concentration of Sm3+ ions rise. The temperature-dependent PL (TDPL) and activation energy results show that the as-synthesized phosphor has considerably superior thermal stability. The results of the current research contemplate us the applicability of Sm3+ ions doped LBW phosphor for photonic devices such as w-LEDs.

Enhancement of upconversion luminescence in Yb3+/Er3+-doped BiVO4 through calcination

Dopant concentration is generally increased in order to enhance the emission efficiency of the upconversion phosphor materials. However, a higher doping concentration generally results in concentration quenching of the upconversion emission resulting in low upconversion efficiency. In such instances, the calcination technique can offer an alternate way of enhancing the emission efficiency of the upconversion phosphors. Here, Yb3+/Er3+-doped BiVO4 has been synthesized by microwave hydrothermal process and the as-synthesized phosphor was calcined at 900 °C in air. Yb3+/Er3+-doped BiVO4 phosphor has been systematically characterized. The elemental distribution is homogeneous. Phase change has occurred from the tetragonal BiVO4 of the as-synthesized sample to the mixture of tetragonal and monoclinic BiVO4 in the calcined sample. The bandgap of the calcined sample has been reduced by 0.52 eV as compared to the as-synthesized one. Under 980 nm excitation, the calcined sample shows ∼ 7 and 15-fold enhancement in the upconversion and downshifting emission intensity, respectively, as compared to the as-synthesized sample. The calcination is found to have increased the lifetime of all the emitting excited states resulting in enhanced emission efficiency which has been confirmed by the time-resolved photoluminescence measurements.

Photoluminescence characteristics of a novel orange red-emitting Eu3+ doped K3Ca2(SO4)3F phosphor for W-LED

The present work reported the synthesis of Eu3+-activated K3Ca2(SO4)3F sulfate-based phosphors via a solid-state reaction method (SSR). The crystal structure of as-synthesized phosphor was studied by XRD analysis. The PL and PLE spectrum were investigated using photoluminescence spectroscopy. The PL excitation spectrum monitored at 616 nm shows sharp line excitation peaks at 395 nm,466 nm and 535 nm, attributes to 7F0→ 5L6,7F0→ 5D2, and 7F0→ 5D1 transitions respectively. The PL spectrum under UV excitation of 395 nm exhibits emission in the red region centered at 592 nm and 616 nm, corresponding to 5D0→ 7F1, and 5D0→ 7F2 transitions of Eu3+ ions in the host. The CIE coordinates confirm the emission in the orange-red region positioned at (0.6824, 0.3175) with color purity of 97.37% and CCT 3872.2 K. The obtained outcome reveals that the reported K3Ca2(SO4)3F: Eu3+ phosphor is the best candidate as UV excitable orange-red emitting phosphor for w-LEDs.

Tetracoordinate Fe3+ Activated Li2ZnAO4 (A = Si, Ge) Near-Infrared Luminescent Phosphors.

Fe3+-doped near-infrared (NIR) phosphors have received a lot of interest because they are nontoxic, inexpensive, and ecologically benign. In this work, Fe3+-activated Li2ZnAO4 (A = Si, Ge) phosphors were synthesized by solid-phase reactions, in which Fe3+ entered the Zn2+ tetrahedral site. When excited by 300 nm UV light, broad NIR emission bands at 750 nm (Li2ZnSiO4: Fe3+) and 777 nm (Li2ZnGeO4: Fe3+) were observed, with internal quantum efficiencies (IQE) of 62.70% (Li2ZnSiO4: Fe3+) and 30.57% (Li2ZnGeO4: Fe3+). The thermal stability was increased from 35.43 to 49.79% at 373 K via cationic regulation. The combination of activation energy, electron-phonon coupling, and Debye temperature explained the improved thermal stability of Li2ZnGeO4: Fe3+ phosphor. Besides, the as-synthesized phosphor demonstrated sensitive and selective Cu2+ ion detection.

Structural, optical, and luminescence properties of Dy3+ -activated potassium calcium silicate phosphor for white light-emitting diodes.

A dysprosium (Dy3+ )-activated potassium calcium silicate (K4 CaSi3 O9 ) phosphor was prepared using a solid-state synthesis route. The phosphor had a cubic structure with the space group Pa as confirmed using X-ray diffraction (XRD) measurements. Details of surface morphology and elemental composition of the as-synthesized undoped KCS phosphor was obtained using scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) spectroscopy. The chemical structure as well as the vibrational modes present in the as-prepared KCS phosphor was analyzed using Fourier transform infrared (FT-IR)spectroscopy. Diffuse reflectance spectra (DRS) were used to determine the optical bandgap of the phosphors and were found to be in the optical range 3.52-3.71 eV. Photoluminescence (PL) spectra showed intense yellow emission corresponding to the 4 F9/2 →6 H13/2 transition under 350 nm excitation. Commission International de l'Eclairage colour chromaticity coordinates were evaluated using the PL spectral data lie within the white region. Dexter theory and the Inokuti-Hirayama (I-H) model were applied to study the nature of the energy transfer mechanism in the as-prepared phosphors. The relatively high activation energy of the phosphors was evaluated using temperature-dependent PL (TDPL) data and confirmed the high thermal stability of the titled phosphor. The abovementioned results indicated that the as-prepared KCS:Dy3+ phosphor was a promising candidate for n-UV-based white light-emitting diodes.

Structural and photoluminescence properties of Sm3+ ions doped strontium yttrium tungstate phosphors for reddish-orange photonic device applications

In the present research work, Sm3+ ions doped Strontium Yttrium Tungstate (Sr9Y2W4O24) phosphors entitled to emit reddish-orange light have been synthesized using the conventional solid-state reaction method and analyzed their structure and phase using X-ray diffraction (XRD) patterns. The diffraction peaks of the Sr9Y2W4O24 phosphor matches very well with the standard JCPDS pattern with card no. 49-0568. The morphological behaviour of the as-synthesized phosphor has been studied using scanning electron microscopy (SEM). Different vibrational bands present in the titled phosphor have been examined using Fourier Transform Infrared (FT-IR) spectroscopy. The optical band gap values of the as-synthesized phosphors have been measured using diffuse reflectance spectra (DRS). The photoluminescence (PL) spectral features recorded for Sm3+ ions activated Sr9Y2W4O24 phosphor under 405 nm excitation reveal strong visible reddish-orange emission at 604 nm pertaining to the 4G5/2 → 6H7/2 transition of Sm3+ ions. Also the PL spectra show concentration quenching at 2 mol% of Sm3+ ions doped in to them. From the recorded PL spectra, the CIE chromaticity coordinates estimated for Sr9Y2W4O24:2.0mol% of Sm3+ phosphor are falling in deep visible reddish orange region. The PL decay spectral profiles recorded at 604 nm emission under 405 nm excitation are showing double exponential behavior and the experimental lifetimes are found to be decreasing with increase in Sm3+ ions concentration in the assynthesized phosphors. The temperature-dependent PL (TD-PL) measurements demonstrate relatively better thermal stability for the as-synthesized phosphor. All the investigations carried out finally allows us to contemplate the suitability of Sm3+ ions doped Sr9Y2W4O24 phosphor for reddish-orange photonic device applications.

Cyan-to-yellow color tunable NaAlSiO4:Eu2+ with high quantum efficiency and thermal stability for white light-emitting diodes

Phosphor-converted white light-emitting diodes (white pc-LEDs) require efficient and thermal stable phosphors with broad-band emission to fulfill the requirement of high-quality illumination. In this work, Eu2+-activated nepheline, NaAlSiO4:Eu2+ with tunable emission was synthesized successfully. The emission band can be tuned from cyan to yellow region through changing flux, synthetic temperature, and/or Eu2+ doping content without changing crystal structure. The tunable emission is due to the variation of occupancy of Eu2+ on two different Na crystallographic sites. Results indicate that using H3BO3 as flux, increasing synthetic temperature and Eu2+ content are beneficial to efficient yellow emission of NaAlSiO4:Eu2+. Na0.92AlSiO4:0.04Eu2+ synthesized at 1300 °C with H3BO3 has high internal (95.14%) and external (78.14%) quantum efficiencies. It also exhibits excellent thermal stability that the emission intensity keeps nearly unchanged within 100 °C. The fabricated proto type white pc-LED by using the phosphor as a yellow component has a color rendering index of 92.0. These results indicate that the as-synthesized phosphors have great potential for application in white pc-LED devices.

Rare earth ions doped Bi2MoO6 luminescent materials: Pechini sol-gel synthesis, down-conversion and up-conversion multicolor emissions, and potential applications

A series of rare earth ions (Eu3+, Sm3+, Yb3+/Er3+, Yb3+/Ho3+, Yb3+/Tm3+) doped bismuth molybdate (Bi2MoO6) phosphors with excellent multicolor luminescence have been synthesized by a facile Pechini sol-gel method. XRD, EDX, and XPS results confirm the highly crystalline orthorhombic phase of Bi2MoO6 and verify that the rare earth ions (RE3+) are effectively integrated into the Bi2MoO6 matrix. During the synthesis process, the calcination conditions play an important role in obtaining the luminescent host matrix, and the optimal calcination condition for the Bi2MoO6 products is determined of 800 °C for 2 h. The Eu3+ and Sm3+ doped Bi2MoO6 samples display intense red and orange-red light under UV/visible excitation whereas the Yb3+/Ln3+ (Ln = Er, Ho, and Tm) doped Bi2MoO6 materials emit green, green, and blue colors when excited by NIR light. Both down-conversion (DC) and up-conversion (UC) multicolor luminescence are obtained by doping the proper Ln3+ activators into the Bi2MoO6 host. The doping concentrations of various RE3+ ions are optimized to generate advantageous phosphors and the luminescence mechanisms of RE3+ ions are systematically studied. The LED devices fabricated by Bi2MoO6:Yb3+/Ln3+ UC phosphors exhibit dazzling multicolor emissions under an injection current, which directly discloses that the as-prepared materials may be of great potential in LEDs and optoelectronic devices. Interestingly, the Bi2MoO6:Yb3+/Er3+/Eu3+ phosphors can simultaneously exhibit red and yellow-green DC emissions and green UC light under excitation of 464, 488, and 980 nm. The multi-mode emission features illustrate that the as-synthesized phosphors may have application prospects in anti-counterfeiting applications.

Photoluminescence investigation of Tb3+-activated barium lutetium oxide microphosphor for latent fingerprint visualization

The feasibility of utilizing the microphosphor Ba3Lu4O9:Tb3+ in latent fingerprint visualization was explored in this work. The micromorphology and elemental composition of the phosphor particles were examined by X-ray photoelectron spectroscopy and transmission electron microscopy. The photoluminescence performance of Ba3Lu4O9:Tb3+ was characterized by the photoluminescence emission and excitation spectra together with the fluorescence decay curves. All the as-synthesized phosphors could be pumped by the ultraviolet, and the photoluminescence spectra consisted of line peaks from the typical 4 f→4 f transitions of Tb3+. The Ba3Lu3.98O9:0.02Tb3+ gave off intense green emission with CIE coordinate of (0.2904, 0.5430). The emission of this phosphor was well matched with the photopic luminosity curve. The photoluminescence intensity of the phosphor recorded at 425 K retained 77.8% of that at room temperature. Furthermore, in the fingerprint visualization experiment, based on this phosphor, the multilevel characteristics of LFP attached with the as-studied phosphor could be clearly identified. All the results signified that Ba3Lu4O9:Tb3+ microphosphor was a promising candidate for latent fingerprint visualization.

Structure and luminescence of a high-efficient blue-red-emitting Na2BaMg(PO4)2: Eu2+, Mn2+ phosphor for plant growth LEDs

New dual-emitting phosphor Na2BaMg(PO4)2: Eu2+, Mn2+ is prepared via conventional sintering method. The structural and luminescent properties of as-synthesized phosphor were systematically studied by experimental characterization and theoretical calculation. Utilizing the Eu2+→Mn2+ energy transfer, this phosphor exhibits efficient double-band emissions at 415 and 620 nm, which has a good match with the absorption spectra of chlorophyll A/B and phytochrome in plants. The energy transfer mechanism had been investigated through emission intensity and decay lifetime variation using Reisfeld's approximation method. Na2BaMg(PO4)2: Eu2+, Mn2+ shows promising properties like good thermal stability (75% emission intensity maintenance at 200 °C) and high quantum efficiency (QE > 80%). A prototype LED was fabricated using optimized phosphor and NUV chip, which exhibits two distinct emission peaks modulating an optimum action spectrum for plant absorption. All results indicate that Na2BaMg(PO4)2: Eu2+, Mn2+ is of great potential as converted component for plant growth LEDs.

Deep blue, cyan, orange-red, and white multicolor emissions generated by Bi3+/Eu3+ activated KBaYSi2O7 luminescent materials for white light-emitting diodes

A variety of Bi3+ and/or Eu3+ doped KBaYSi2O7 phosphors with deep blue, cyan, orange-red, and white light multicolor emissions have been fabricated by a Pechini sol-gel (PSG) method. The KBaYSi2O7:Bi3+ phosphors exhibit an intense cyan emission or a unique narrow deep blue emission when excited by different wavelengths, which may bridge the cyan gap or act as a promising deep blue phosphor for white light-emitting diodes (WLEDs). The tunable multicolor emissions can be achieved by changing the Bi3+ doping concentrations. The Bi3+/Eu3+ co-doped KBaYSi2O7 phosphors display intrinsic emissions of Bi3+ and Eu3+ and an energy transfer process between Bi3+ and Eu3+ can be detected. The luminescence colors of KBaYSi2O7:Bi3+,Eu3+ regularly shift from blue, through cold and warm white, finally toward orange-red by adjusting the relative doping concentrations of Bi3+ and Eu3+. The single-phase white light-emitting material can be generated in both cold and warm white regions by simply varying the Eu3+ doping concentrations. Furthermore, three kinds of WLEDs devices are fabricated by KBaYSi2O7:Bi3+ or KBaYSi2O7:Bi3+,Eu3+ phosphors, which can exhibit dazzling white light emissions with eminent CIE coordinates, correlated color temperature, and color rendering index. The result offers direct evidence that the as-synthesized phosphors may be potentially applied in WLEDs and solid-state lighting.

Influence of inorganic salt on morphology, particle size, and luminescence properties of lanthanide ions doped Na0.5Gd0.5MoO4 microcrystals

A variety of tetragonal Na0.5Gd0.5MoO4 microcrystals with different morphologies, dimensions, side lengths, and heights (microplates, tetragonal, and quasi-cubic structures) have been synthesized by a novel inorganic salt assisted hydrothermal approach. The influence of the addition of inorganic salt NaNO3 on the phase structure, morphology, particle size, and luminescence performance of the samples has been systematically studied for the first time. A series of Na0.5Gd0.5MoO4:Ln3+ (Ln = Eu, Tb, Dy, Sm, Yb/Er, Yb/Tm, Yb/Ho) phosphors with excellent down-conversion or up-conversion luminescence properties have been synthesized by doping proper rare earth activator ions into the host matrix. The addition of inorganic salt NaNO3 and the calcination process can greatly improve the luminescence performances of the phosphors, which can be ascribed to the decrease of surface area and enhanced crystallinity of the Na0.5Gd0.5MoO4 crystals. The as-obtained down-conversion and up-conversion multicolor luminescent materials show the intense characteristic emissions of Ln3+ and eminent thermal stability. Moreover, the corresponding LED devices fabricated by the phosphors display dazzling multicolor emissions, which directly verifies that the as-synthesized phosphors may have the prospect to be utilized in the field of optoelectronic devices and LEDs.

Novel near-ultraviolet-excited and thermally-stable blue-emitting phosphor for healthy WLED lighting

The widespread popularity of white light-emitting diodes (WLED) lighting results in a chronic exposure to blue light, which has negative impacts on human biological functions, emotions and health. As an alternative strategy, integrating near-ultraviolet (n-UV) LED chips with high-efficiency (high quantum efficiency, chemical and thermal stability) tricolor phosphors, can easily achieve high-quality white light and diminish the so-called “blue-light hazard”. However, few blue-emitting phosphors can meet the aforementioned requirements. Herein, we report a novel n-UV excited bright blue-emitting CsBaB9O15:2%Eu2+ phosphor with high internal quantum efficiency (IQE = 68.8%) and outstanding thermal stability (94.2%@ 150 °C, 84%@ 250 °C). Impressively, this phosphor exhibits excellent chromaticity stability (Δx = 0.002, Δy = 0.012; 3.6 × 10−3 ≤ ΔE ≤ 8.1 × 10−3) from 25 to 150 °C. These remarkable thermal stability are mainly ascribed to the large band gap of host (Eg = 5.85 eV), which effectively suppresses the thermal ionization pathway of the dominant 440 nm emission in the CsBaB9O15:2%Eu2+ phosphor. A WLED device was fabricated by combining commercial phosphor Sr2Si5N8:Eu2+, green phosphor (Sr, Ba)2SiO4:Eu2+ and as-synthesized blue phosphor with a 380 nm n-UV LED chip, which exhibits high color-rendering index (CRI = 90) and low correlated color temperature (CCT = 3301 K). These results demonstrate that the outstanding CsBaB9O15:Eu2+ blue phosphor could be a candidate for next-generation healthy WLED lighting.

UV-excited blue- to green-emitting Tb3+ -activated sodium calcium metasilicate colour tunable phosphor for luminescence devices.

Tb3+ -doped Na4 Ca4 Si6 O18 (NCMS:Tb3+ ) phosphors were synthesized using a solid-state reaction route with increasing dopant concentration. The phase identification studies for NCMS:Tb3+ phosphors were carried out using an X-ray diffraction (XRD) technique. The XRD patterns for the as-synthesized phosphors showed satisfactory agreement with the standard pattern (JCPDS card no. 75-1687) for the pure phase of the Na4 Ca4 Si6 O18 compound. The morphology and size of particles were illustrated from scanning electron microscope (SEM) micrographs. The photoluminescence excitation (PLE) spectrum of Tb3+ -doped Na4 Ca4 Si6 O18 phosphor depicts the strong excitation peak obtained in the UV spectral region. The trivalent terbium-activated NCMS phosphors excited in the UV region (232 nm wavelength) exhibited intense emission in the blue (350-470) and green (470-650) spectral regions. When increasing the concentration of Tb3+ ions in the host matrix, the emission colour shifted from the blue to the green region due to cross-relaxation energy transfer (CRET) mechanisms and showed the tunable behaviour of the Tb3+ -activated as-synthesized NCMS phosphor. These results demonstrated that the Tb3+ -activated sodium calcium metasilicate phosphor has immense potential to contribute as a green- and blue-green-emitting component in lighting and display device applications.

Improvement of self-activated luminescence properties of Ca2KZn2(VO4)3 down-conversion materials by SSR method based on co-doped Eu3+,Dy3+ rare earth ions concentrations

In this study, a self-activated and co-doped Eu, Dy with Ca2KZn2(VO4)3 (CKZVO) phosphors were synthesized by conventional solid state reaction method. The powder X-Ray diffraction study confirm the formation of single phase cubic crystal structure with space group Ia3̅d. The surface morphology of as-synthesized phosphor was verified by SEM analysis. The FTIR spectrum shows characteristic bonds, for bending vibration and asymmetric stretching vibration. In photoluminescence under the UV excitations the CKZVO phosphor display greenish blue emission due to the VO4 transitions ions in host matrix. The PL characteristic of CKZVO: Dy3+ phosphors exhibits intense emission centred at 480 nm (blue) and 573 nm (yellow color). Moreover, CKZVO: Eu3+ phosphor exhibits strong emission at 500 nm (green) and 615 nm (Red) under UV excitation. Further co-doping of Dy3+, Eu3+ in the host matrix reveals a strong emission in blue, green, yellow and red region. The chromaticity coordinates of the samples were in near white region. All the results exhibit that CKZVO: Dy3+, Eu3+ phosphor might be a potential material for NUV-based white light-emitting diodes.

A garnet-structured (Y, Ca)3(Al, Mg)2(Al, Si)3O12:Ce3+ phosphor-in-glass engineering for use in high color rendering white LEDs

White light emitting diodes (LEDs) suffer from two most common drawbacks: the deficiency of the red component and the poor thermal stability of silicone. Ce3+-doped garnet phosphors with tailor-made luminescence properties can be achieved by variations in {A}, {B}, and {C} cation sites. Herein, a simultaneous ion co-substitution design strategy has been adopted to synthesize a series of (Y, Ca)3(Al, Mg)2(Al, Si)3O12 garnet phosphors and corresponding phosphor-in-glass (PiG) films. The co-substitution is finely restricted to the assigned sites. The emission peak is shifted from 529 to 565 nm, which is beneficial to obtain low color temperatures and high color rendering using a single phosphor for white LEDs. By employing the as-synthesized phosphor, the corresponding PiG films were fabricated by the low temperature co-sintering technology using the SiO2–B2O3–ZnO–Na2O glass system characterized with excellent thermal stability and moisture resistance. The morphological and elemental analyses demonstrated that the as-made phosphor powders were uniformly distributed in the glass host without any interfacial reactions. Finally, modular white LEDs with a high color rendering (Ra = 82.7) is achieved through the as-synthesized PiG film on an InGaN blue chip. This study may open up a facile approach to obtain high quality luminescence based on the mono-luminescence center, avoiding excitation energy wastage and low quantum efficiency aroused by multi-luminescence centers or color compensation phosphors in glass.