Luminescence Properties Of Phosphors Research Articles

The effect of doping Mg2+ on structure and properties of Sr(1.992-x)MgxSiO4: 0.008Eu2+ blue phosphor synthesized by co-precipitation method

In order to improve the luminescence property of silicate phosphors, a series of Sr(1.992-x)MgxSiO4: 0.008Eu2+(x = 0, 0.25, 0.50, 0.75) blue phosphors have been synthesized using one-step calcination of a precursor prepared by chemical co-precipitation. And then the crystal structure and luminescence properties of the phosphors are investigated by means of X-Ray Diffraction and spectrophotometer. The results show that β-phase existed in the mixed phases of Sr2SiO4 (β+α′) would transform to α′-phase with Mg2+ ions doping into the silicate host until it disappeared. On the other hand, the introduction of Mg2+ ions can enhance the intensity of the excitation spectrum and promote the excitation sensitivity of Sr(1.992-x)MgxSiO4: 0.008Eu2+ phosphors in NUV region. Under NUV excitation at 350 nm, all samples exhibit a broadband emission in range of 400–550 nm due to the 4f65d1→4f7(8S7/2) transition of Eu2+ ions. According to Multi-peak fitting to emission spectra by Gauss method, the broad emission band consists of two single bands with peaks Em1 and Em2 locating at 460 and 490 nm, which corresponds to Eu2+ ions occupying the ten-fold oxygen-coordinated Sr1 site and the nine-fold oxygen-coordinated Sr2 site, respectively. The luminescence intensity of Sr(1.992-x)MgxSiO4:0.008Eu2+(x = 0, 0.25, 0.50, 0.75) blue phosphors has been enhanced remarkably after Mg2+ ions are added. Meanwhile, the chromaticity coordinates change from the blue-green region to the blue region as x moves from 0 to 0.75. Moreover, the decay curves are measured and can be well fitted with double exponential decay equation. It shows that the average lifetime is extended with the concentration of Mg2+ ions increasing. These results indicate that Sr(1.992-x)MgxSiO4: 0.008Eu2+(x = 0, 0.25, 0.50, 0.75) can be used as a potential blue phosphor in near UV-excited white LEDs.

Enhancing emission intensity and thermal stability by charge compensation in Sr2Mg3P4O15:Eu3+

AbstractCharge compensation was the effective methods to enhance the luminescence properties of phosphors. In this paper, novel single‐phased orange light emitting Sr2Mg3P4O15:Eu3+ phosphors were prepared by solid state method. The phase purity and luminous characteristics were examined in detail. Meanwhile, three kinds of charge compensation methods (co‐doping the alkali metal R+ (R+ = Li, Na, and K), substituting Si4+ for P5+ and self‐compensation) were employed to solve the charge imbalance problem between Sr2+ and Eu3+. The results showed that emission intensity of Eu3+ was improved by 1.43 (Li+), 1.58 (Na+), 1.53 (K+), 1.61 (Si4+), and 1.30 (self) times than that of Sr1.6Mg3P4O15:0.40Eu3+, respectively, and there was no change in the emitting color simultaneously. Furthermore, as the temperature reached at 423 K, the emission intensity increased from 41.67% of Sr1.6Mg3P4O15:0.40Eu3+ to 55.69% (Li+), 61.62% (Na+), 58.98% (K+), 71.15% (Si4+), and 80.59% (self) of that at room temperature. The reasons of those phenomena were the reduction in ion vacancies caused by charge imbalance through the charge compensation process. The specific mechanisms were elaborated in detail. Overall, this research validated that the charge compensation strategies could be severed as the key method to improve the luminescence properties, especially the thermal stability of phosphor.

The Role of Auxiliary Alkali Metal Ions on Scheelite Structure Double Molybdate and Tungstate Phosphors.

Eu3+-doped alkali metal double molybdate and tungstate phosphors, (MEu) (Mo,WO4)2 (MEM and MEW, M = Li+, Na+, and K+), have been identified as potential candidate materials for white light-emitting diodes. However, there are no systematic considerations of the role of auxiliary alkali-metal ions (AMIs) on the structural, chemical, and luminescent properties of these phosphors. Here, a systematic investigation to elucidate the role of AMIs on MEM and MEW phosphors was performed using ab initio calculations based on experimental evidence. The results from experimental assessments with intensive structural and chemical bond analyses reveal a clear dependence of AMIs on the structural and luminescent properties of phosphors. The structural changes due to AMIs originate from a bond length change between AMIs-O2- bonds, and AMIs had minor effects on the other bonds. A phase transition induced by K+ ions originates from not only structural factors but also local chemical bonding characteristics. Overall, the results indicate that the major role of AMIs is to induce phosphor structural changes, and the effects on the chemical properties are minor. The results of this study shed light on developing not only MEM and MEW phosphors but also new phosphor materials using auxiliary metal ions.

The effect of Y3+ and Eu3+ on properties of Zn3V2O8 phosphor

In this paper, the (Zn1-xYx)3V2O8 and (Zn1-xEux)3V2O8 phosphors were successfully prepared by high temperature solid state method. The effect of the doping amount of Y3+ and Eu3+ on the luminescent properties of phosphors was discussed. The phase, surface morphology and luminescent properties of the phosphors were characterized by X ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence (PL). The results show that the phosphor is the target product, the sample of the composite particles is bulky, the excitation spectral range of (Zn1-xYx)3V2O8 phosphors is 300-400nm, the excitation peak is at 361nm, and (Zn1-xYx)3V2O8 phosphor emission spectra in the range of 420-690nm, the emission peak in 559nm. The results show that the crystal structure of Zn3V2O8 and (Zn1-xEux)3V2O8 were the same, and the particle uniformity of (Zn1-xEux)3V2O8 was better than Zn3V2O8. The emission band Zn3V2O8 and (Zn1-xEux)3V2O8 were present at the wave length of 420-690 nm, the luminescence property of (Zn1-xEux)3V2O8 was enhance by Eu-doped.

Dopant Concentration induced optical changes in Ba1−xEuxMoO4: A green and facile approach towards tunable photoluminescent material

Ba1−xEuxMoO4 phosphors were synthesized by complex polymerization method. The prepared phosphor material was extensively characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermogravimetry (TG) and differential thermal analysis (DTA). The introduction of europium upto 2mol% doesn’t change the crystal structure. The influence of Eu concentration on the luminescent properties of phosphors was analyzed. It was seen that, under UV irradiation, the pure BaMoO4 sample shows multicolor emission. The blue and green emission was attributed to 1T2 → 1A1 transition within MoO42− moeity (shallow defects), whereas the red- orange emission to the defect MoO3 group (deep defects). The intensity of magnetic dipole transition (MDT) was found to be lower than that of electric dipole transition (EDT) which indicates the low -⁠ symmetry acentric environment of Eu3+ ions. Based on Stark splitting, the actual site symmetry of Eu3+ in BaMoO4 was clarified as C6v; reduced from actual S4 for Ba2+ ion in BaMoO4. The decay curve shows two different lifetime value 11.2 µs (τ1) (host contribution) and 693 µs (τ2) (europium sitting at Ba2+ site) with magnitudes 14% and 86% respectively. The value of host dopant energy transfer efficiency calculated under forbidden f-f transition excitation was found to be lower at 12.6% as compared to 76% in case of excitation by allowed charge transfer band. To find out the concentration quenching mechanism, the critical energy-transfer distance for the Eu3+ ions was evaluated to be 33.81Å, which was found to be greater than 10Å and signify electric multipolar interactions as the only mode of energy transfer The intensity of peaks corresponds to EDT was found to be high in comparison to the peak due to MDT in all the Eu- doped samples: indicating the asymmetric local site symmetry around Eu3+. This is also reflected in the JO (Judo Ofelt) parameter trend; at all concentrations, Ω2 value is greater than Ω4 indicating the high covalency of the Eu3+ ligand bonding and asymmetric environment around europium ion in BaMoO4, which is highly probable because it occupies the asymmetric Ba2+ position.

Luminescence properties and energy transfer of Tb3+–Eu3+ co-doped Sr3B2O6 phosphors

A series of single-composition phosphors Sr3B2O6: Tb[Formula: see text], Eu[Formula: see text]have been prepared via a combustion method. The structural and luminescent properties of phosphor are investigated in detail. Under ultraviolet radiation excitation, Sr3B2O6: Tb[Formula: see text], Eu[Formula: see text] phosphors show the characteristic [Formula: see text]–[Formula: see text] transitions of both Eu[Formula: see text] and Tb[Formula: see text] and give a bright yellow emission. The investigations on photoluminescence and lifetime of Eu[Formula: see text] show that there are two sites of luminescence center of Eu[Formula: see text] in host matrix. The energy transfer from Tb[Formula: see text] ion to Eu[Formula: see text] ion are observed and the mechanism of energy transfer is dipole–quadrupole interaction.

Tunable luminescence and energy transfer properties in Ca2−xNaMg2V3O12:xEu3+ phosphors

Novel broadband luminescence phosphors Ca2−xNaMg2V3O12:xEu3+ have been successfully prepared via the conventional high-temperature solid-state reaction. The effects of concentrations of doped Eu3+ and introducing Li+, K+ on the luminescent properties of phosphor were studied. X-ray diffraction, GSAS structural refinement and photoluminescence spectra were used to characterize the samples. The refinement data ensured where the doped Eu3+ ions occupied the lattice site in the host. Under 355 nm excitation, the emission peak of Ca2NaMg2V3O12:Eu3+ phosphors are located at 610 nm (red) ascribed to the electric dipole transition of Eu3+ from 5D0 → 7F2. In the range of 400–575 nm, Ca2NaMg2V3O12:Eu3+ phosphors have broad emission bands attributed to charge transfer of $${\text{VO}}_4^{3 - }$$ group. Energy transfer mechanism, energy transfer efficiency and critical distance (Rc) of $${\text{VO}}_4^{3 - }$$ → Eu3+ would be analyzed. The emitting color of Ca2NaMg2V3O12:Eu3+ could be tunable from blue-green to near white light.

Single-phased trichromatic white light-emitting Ca6BaP4O17:Sm3+, Ce3+, Eu2+ phosphor for UV-light-emitting diodes

Eu2+, Sm3+, Ce3+ co-doped single-phased tunable color conversion phosphor for W-LED was prepared by high-temperature melting under reducing atmosphere. X-ray diffraction and photoluminescence spectra were utilized to characterize the structural and luminescence properties of the as-synthesized phosphors. A strategy of Sm3+ doping was used with the aim of providing red color luminescence, with several sharp emission peaks appearing at 567, 603, 651, and 715 nm ascribed to the 4f–4f transitions of Sm3+. as well as a broad band from 420 to 580 nm due to the spectra overlap between the emission band of Ce3+ and Eu2+, corresponding to the 5d–4f transition of Eu2+ and 5d–4f transition of Ce3+. The luminescence properties of the phosphor with different molar ratios of Eu2+/Ce3+/Sm3+ were studied, and the corresponding chromaticity coordinates were calculated. The ultraviolet light-emitting diode (UV-LED)-excitable phosphors emitting white light were obtained by tuning the relative emission intensities of Eu2+, Ce3+, and Sm3+. The results indicate that the Eu2+/Ce3+/Sm3+ co-doped Ca6BaP4O17 phosphor can be used as a potential matrix material for white LED under UV-LED.

Conversion of Biowaste Asian Hard Clam (Meretrix lusoria) Shells into White-Emitting Phosphors for Use in Neutral White LEDs.

The increasing volume and complexity of waste associated with the modern economy poses a serious risk to ecosystems and human health. However, the remanufacturing and recycling of waste into usable products can lead to substantial resource savings. In the present study, clam shell waste was first transformed into pure and well-crystallized single-phase white light-emitting phosphor Ca9Gd(PO4)7:Eu2+,Mn2+ materials. The phosphor Ca9Gd(PO4)7:Eu2+,Mn2+ materials were synthesized by the solid-state reaction method and the carbothermic reduction process, and then characterized and analyzed by means of X-ray diffraction (XRD) and photoluminescence (PL) measurements. The structural and luminescent properties of the phosphors were investigated as well. The PL and quantum efficiency measurements showed that the luminescence properties of clam shell-based phosphors were comparable to that of the chemically derived phosphors. Moreover, white light-emitting diodes were fabricated through the integration of 380 nm chips and single-phase white light-emitting phosphors (Ca0.979Eu0.006Mn0.015)9Gd(PO4)7 into a single package of a white light emitting diode (WLED) emitting a neutral white light of 5298 K with color coordinates of (0.337, 0.344).

Luminescence study of Eu3+-doped garnet phosphors: Relating structure to emission

A series of Eu3+-doped garnets of the general formula A3B2X3O12 (A = Sr,Ca; B=Sc,Y; X = Si,Ge) was obtained using a high temperature solid state reaction. These compounds were characterized by X-ray diffraction and photoluminescence spectroscopy. The relation between the luminescence properties of phosphors and their host lattice composition was studied. It was found that Eu3+ ions occupied the A site in compounds with smaller cell volume (Ca3Sc2Si3O12, Ca3Sc2Ge3O12 and Sr3Sc2Ge3O12) and both A and B sites in compounds with bigger cell volume (Ca3Y2Ge3O12 and Sr3Y2Ge3O12). This study showed the relationship between the host lattice composition and the energy of the charge transfer (CT) transition, 4f→4f/CT, 5D0→7F2/5D0→7F1 and 5D0→7F4/5D0→7F1 intensity ratios and splitting of the 7F1 level by the crystal field. Decay times of the Eu3+ luminescence were measured and correlated with the compositionally-dependent structural changes.

Synthesis and luminescence properties of Sr3MgSi2O8:Ce3+,Tb3+ for application in near ultraviolet excitable white light-emitting-diodes

The alkaline-earth silicate Sr3MgSi2O8:Ce3+,Tb3+ phosphors have been synthesized via conventional high temperature solid-state method. The crystal structure, luminescence properties, morphology of phosphors are investigated systematically. The thermal quenching and concentration quenching mechanisms of phosphors are also discussed. The phosphors can be excited under near ultraviolet light ranging from 200 nm to 450 nm. The calcination temperature and calcination time are significant factors for luminescence property of phosphors. Increasing co-doping Tb3+ makes the emission intensity of Ce3+ decreases proportionally while the emission of Tb3+ increases. It indicates that it exists energy transfer between Ce3+ and Tb3+. The emission wavelength can be tuned from bluish violet region to blue region. The results imply Sr3MgSi2O8:Ce3+,Tb3+ phosphors can be a potential candidate for solid-state lighting.

Crystal structure and luminescent property of flaky-shaped Sr4Al14O25:Eu2+, Dy3+ phosphor doped with Er3+ ions

In this study, the afterglow properties of Sr4Al14O25:Eu2+, Dy3+ was successfully improved and the absorption in the visible region (>400 nm) was increased using co-doped Er3+ ions, thus facilitating the application of Sr4Al14O25:Eu2+, Dy3+ in daylight environment. A series of Sr3.88−xAl14O25:0.04Eu2+, 0.08Dy3+, xEr3+ (x = 0, 0.04, 0.08, 0.12, 0.16, and 0.20) phosphors were prepared using a conventional high-temperature solid-phase method; their structures were characterized by XRD, TEM, HRTEM, FT-IR, and XPS. The luminescence properties, with excitation at 275 nm and 360 nm, were systematically compared and analyzed by fluorescence spectra, afterglow spectra, and afterglow decay spectra. Interestingly, although the Er3+ doping slightly affected the crystal structure of Sr4Al14O25:Eu2+, Dy3+ phosphor, the luminescent properties of phosphors were affected to a large extent. After the Er3+ doping, the emission peak of Eu2+ at 485 nm split into three peaks at 481 nm, 492 nm, and 529 nm. An appropriate Er3+ doping significantly enhanced the afterglow performance of the phosphors, whereas excessive Er3+ doping caused concentration quenching. The absorption in the visible region (>400 nm) increased with Er3+ doping, which was more suitable for the application of Sr4Al14O25:Eu2+, Dy3+ in daylight environment. The initial afterglow intensities with 360 nm excitation were higher than those with 275 nm excitation, whereas the afterglow time of the former was slightly shorter than that of the later. The one-dimensional and two-dimensional lattice fringe phase of the local particles can be observed clearly from HRTEM of flaky-shaped Sr3.76Al14O25:0.04Eu2+, 0.08Dy3+, 0.12Er3+ particle, which was rare in the previous reports. Moreover, the preliminarily enhancing mechanism of Er3+ on the luminescent properties of Sr3.88Al14O25:0.04Eu2+, 0.08Dy3+ phosphor was analyzed.

Preparation, characterization and luminescence properties of a new hydrous red phosphor CaB3 O5 (OH):Eu3+ with different morphologies.

A new borate phosphor CaB3 O5 (OH):Eu3+ with different morphologies was synthesized using a hydrothermal method and its luminescence properties were studied. The effects of surfactants on the crystal structures, morphologies and luminescence properties of the samples were studied. The results showed that the surfactants play an important role in controlling the morphology and improving the luminescence properties of phosphors. The luminescence intensity and R/O(I615/I592) value were enhanced for the prepared sample by adding PEG4000. The prepared sample exhibited a higher R/O than some anhydrous calcium borate phosphors, indicating that this product could serve as a new potential red phosphor.

Photoluminescence properties of Eu3+ ions in yttrium oxide nanoparticles: defect vs. normal sites

The position of activator ions in the lattice has a fundamental effect on the luminescent properties of phosphors.

Single phase tunable warm white-light-emitting Sr_3La(PO_4)_3:Eu^2+, Sm^3+ phosphor for white LEDs

A novel single phased white emitting phosphor Sr3La(PO4)3:Eu2+, Sm3+ was synthesized by the solid-state method, and the crystal structure and luminescence properties of phosphors were investigated in detail by the X-ray diffraction, photoluminescence spectra and decay curves. Through the energy transfer, the warm white light can be realized with superior chromaticity coordinates of (0.3824, 0.3381), low correlated color temperature (CCT = 3598 K), and Ra of 78.4 by varying the molar ratios of Eu2+ and Sm3+ in the Sr3La(PO4)3:Eu2+, Sm3+ phosphor. The results indicate that the developed phosphor can be used as a potential warm white emitting phosphor for white light emitting diodes.

Synthesis and luminescence properties of a new green emitting Ca2MgSi2O7−xNx:Eu2+ phosphor

A nitrogen-contained solid solution Ca2MgSi2O7−xNx:Eu2+ green-emitting phosphor was successfully synthesized by adding Si3N4 powders to Ca–Si–O xerogel in non-reducing atmosphere (pure nitrogen). The microstructure, surface morphology and luminescence properties of phosphors were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence (PL) spectra, respectively. The results show that the crystalline structure of Ca2MgSi2O7−xNx:Eu2+ is exactly consistent with Ca2MgSi2O7, which indicates that N existed as solid solution state in the Ca2MgSi2O7:Eu2+ matrix. The phosphors can be efficiently excited at a wavelength of 350–490 nm and a strong green emission peak is centered at 529 nm which is attributed to 4f65 d1−4f7 transition of Eu2+. It is proved that Eu3+ ions have been reduced into Eu2+ ions when the mixture of Si3N4 and precursor is calcined at 1250 °C in non-reducing atmosphere. In addition, the intensities of PL excitation and emission can be improved significantly and the emission spectra shows red-shift with the increase of N concentration. With the increase of Eu2+ concentration, luminescent intensity of the phosphors increases continuously and reaches a maximum value at the concentration of 1.5 mol% Eu2+. With the further increase of Eu2+ concentration, we can observe the significant decreases in luminescent intensity and the concentration quenching effect.

Color-tunable and luminescence properties of phosphors of Ce3+ and Tb3+ co-doped La5Si3O12N for UV w-LEDs

A series of Ce3+, Tb3+ and Ce3+/Tb3+ co-doped in La5Si3O12N phosphors were synthesized by conventional high temperature solid state reaction method. With the increase of Tb3+, the green emission was realized in (La0.94−yCe0.06Tby)5Si3O12N phosphors on the basis of the efficient energy transfer from Ce3+ to Tb3+ with an efficiency (ηT) over 58.72%. The room temperature PL decay curves of the Ce3+ ions in (La0.94−yCe0.06Tby)5Si3O12N phosphors monitored at 460nm with an excitation at 365nm indicated that the energy transfer process between Ce3+ and Tb3+ indeed took place. The CIE chromaticity diagrams for (La0.94−yCe0.06Tby)5Si3O12N phosphors were also observed, which shows the color tuned from blue to blue-greenish to green with the increase of Tb3+ concentration from 0.01 to 0.08. These results demonstrated that Tb3+ ion with low 4f–4f absorption efficiency in near UV region can play the role of an activator in narrow green-emitting phosphor through efficient energy feeding by allowing 4f–5d absorption of Ce3+ with high oscillator strength. All the results indicated that the Ce3+ and Tb3+ activated La5Si3O12N phosphor may be good candidates for blue-green components in n-UV white LEDs.

Orange-red emitting Eu2+-activated (Sr0.883Ba0.1Lu0.0.17)3(Si0.95Al0.05)O5 phosphor: structure, photoluminescence, and application in white LEDs

Orange-red emitting (Sr0.883-xBa0.1Lu0.0.17Eux)3(Si0.95Al0.05)O5 phosphors were synthesized by conventional solid-state reaction. The effect of NH4F flux on structural and luminescent properties of phosphors was investigated. Results suggested that the optimal content of NH4F flux was 3 wt.% and the optimal doping concentration of Eu2+ was x=0.023 mol. The phosphors showed intense absorption in near-ultraviolet to blue region and exhibited orange-red emissions. The thermal stability of synthesized (Sr0.86Ba0.1Lu0.017Eu0.023)3(Si0.95Al0.05)O5 phosphor were examined and compared with commercial YAG:Ce3+ yellow phosphors. Combining an InGaN blue 460 nm chip and a white-emitting (Sr0.86Ba0.1Lu0.017Eu0.023)3(Si0.95Al0.05)O5 phosphor produced a white- light LED, demonstrating CIE chromaticity coordinates of (0.314, 0.329) and a color temperature of 5595 K. All results showed that this phosphor is a promising candidate as orange-red emitting phosphor for white light emitting diode (w-LED) application.

Preparation and luminescence properties of phosphors of rare earth complexes based on polyoxotungstates

Three new phosphors of rare earth complexes based on polyoxotungstates, K3Cs8[Eu(PW11O39)2]·11H2O (1), K3Cs8[Sm(PW11O39)2]·10H2O (2), and K5Cs6[Dy(PW11O39)2]·15H2O (3) have been prepared and characterized. The crystallographic analyses reveal that these compounds consist of two monovacant keggin anions [PW11O39]7− connected by a rare earth ion in a sandwich structure. The investigations of photoluminescence properties show that phosphor 1 emits strong red light at 614 and 702nm, 2 emits strong orange-red light at 598.7nm, and 3 exists two strong emissions at 479nm (blue) and 574nm (orange). The luminescence properties suggest that the 1 can be applied as the potential red-emitting crystal phosphor, and the 3 may be regarded as a potential white light material for LEDs.

Relationship between structure and luminescence properties in Ce3+ or Ce3+, Mn2+-doped garnet phosphors for use in white LEDs

A series of Ce3+ or Ce3+ and Mn2+ doped garnets of the general formula A3B2X3O12 (A=Sr,Ca; B=Sc,Y; X=Si,Ge) was obtained using a high temperature solid state reaction. These compounds were characterized by X-ray diffraction and photoluminescence spectroscopy. The relation between luminescence properties of phosphors and their host lattice composition was studied. It was found that Ce3+ ions occupied the A site and emitted in the green spectral region. Mn2+ ions can exchange cations in both A and B sites showing green and red emissions, respectively and getting excited due to an energy transfer from Ce3+. This study showed the relationship between Ce3+ and Mn2+ emission/excitation wavelengths and the symmetry around the activator ions expressed by means of the distortion factor of the dodecahedral A site (d88/d81). Decay times of the Ce3+ and Mn2+ luminescence were measured and correlated with the compositional dependent structural changes.