Tri-doped Phosphors Research Articles

Up-conversion of Nd3+/Yb3+/Tm3+ tri-doped CaTeO3 compound under excitation of 808 nm

Nd3+/Yb3+/Tm3+ tri-doped CaTeO3 compounds were prepared by a solid-state reaction method. Bright blue up-conversion (UC) luminescence at around 476 nm, which corresponds to the Tm3+: 1G4 → 3H6 transition, was observed under 808-nm excitation. The Nd3+ → Yb3+ → Tm3+ energy transfer process was responsible for the strong blue up-conversion emission in the tri-doped phosphor. The Tm3+ blue up-conversion emission intensity was strongly dependent on the concentrations of Yb3+ and Nd3+. The possible up-conversion mechanisms for the Nd3+/Yb3+/Tm3+ tri-doped CaTeO3 phosphor are discussed, based on the Nd3+ and Yb3+ concentration-dependent UC spectra, near-infrared luminescence spectra and luminescence decay curves.

A single-phase white light emitting phosphor Ba3Y(PO4)3:Ce3+/Eu2+/Mn2+: Luminescence, energy transfer and thermal stability

Abstract Series of Ce3+/Eu2+, Ce3+/Mn2+ and Ce3+/Eu2+/Mn2+ doped Ba3Y(PO4)3 samples were synthesized by a high temperature solid state reaction method. Phase formation, energy transfer, luminescence properties and thermal quenching properties were investigated carefully. The energy transfer from Ce3+ to Eu2+ and Ce3+ to Mn2+ in Ba3Y(PO4)3 were verified and discussed detailed. When Ce3+ and Eu2+ are co-doped, the energy transfer process from Ce3+ to Eu2+ is confirmed with electric dipole-dipole interaction. For Ce3+/Mn2+ co-doped phosphors, the energy transfer process from Ce3+ to Mn2+ is proved with electric dipole-dipole interaction. Besides, due to the existence of defects, the phosphors show excellent thermal stability. For Ce3+/Eu2+/Mn2+ tri-doped Ba3Y(PO4)3, the energy transfer Ce3+→Eu2+ (Mn2+) and Eu2+→Mn2+ are confirmed. The energy transfer priority among Ce3+, Eu2+ and Mn2+ is analyzed in detail basing on the change of emission intensity. The obtained tri-doped phosphors contain red, green and blue component, thus they can emit warm white light basing on the energy transfer. The results show that they may be novel white-light-emitting phosphors for ultraviolet white light emitting diodes.

Investigations on energy transfer and tunable luminescence spectra for single, co-doped and tri-doped RE3+(RE3+= Dy3+, Sm3+ and Eu3+) activated Sr1.99Bi0.01CeO4 phosphors

The Sr1.99-xBi0.01CeO4:xRE3+ (RE3+ = Dy3+, Sm3+ and Eu3+, x = 0 and 0.03) single, co-doped and tri-doped phosphors synthesized by solid state reaction technique and their structure analysed by X-ray powder diffraction technique (XRD). The results shows that the Dy3+,Sm3+, Eu3+, Dy3+/Sm3+, Sm3+/Eu3+, Dy3+/Eu3+, and Dy3+/Sm3+/Eu3+ ions are effectively studded into the host lattice site without changing the structure of the host. The luminescence and energy transfer properties of the Sr1.99-xBi0.01CeO4:xRE3+ have been investigated for single, co-doped and tri-doped phosphors under each of the 387 nm (Dy3+: 6H15/2 → 4I13/2), 409 nm (Sm3+: 6H5/2 → 6P3/2) and 466 nm (Eu3+: 7F0→5L6) excitation levels wherein the mean emission values reportedly seem to be 572, 651 and 615 nm respectively. The chromaticity coordinates and decay time of the synthesized materials are also examined.

Promising light converting BaMoO4:Er3+-Tm3+-Yb3+ phosphors for display and optical temperature sensing

Er3+-Tm3+-Yb3+ tri-doped BaMoO4 phosphors were synthesized by co-precipitation technique and characterized by X-ray diffraction analysis, absorption study and field emission scanning electron microscopy analysis. Upconversion as well as downconversion luminescence studies were performed by using near infrared (980 nm) and ultraviolet (380 nm) excitations. Energy level diagram, pump power dependence and colour coordinate study were utilized to describe the multicolor upconversion emission properties. Under single 980 nm diode laser excitation the dual mode sensing behaviour is realized via Stark sublevels and thermally coupled energy levels of the Tm3+ and Er3+ ions in the prepared tri-doped phosphors. A comparative fluorescence intensity ratio analysis for integrated emission intensities arising from the Stark sublevels {1G4(a) and 1G4(b)} and thermally coupled energy levels {2H11/2 and 4S3/2} of the Tm3+ and Er3+ ions, respectively was carried out in the prepared tri-doped BaMoO4 phosphors. The maximum sensitivity for thermally coupled energy levels of the Er3+ and Stark sublevels of the Tm3+ ion was reported. The developed phosphors could be useful in the display devices and optical thermometric applications.

Intense blue upconversion emission and intrinsic optical bistability in Tm3+/Yb3+/Zn2+ tridoped YVO4 phosphors

Tm3+/Yb3+/Zn2+:yttrium metavanadate (YVO4) phosphors prepared through chemical coprecipitation and the solid state reaction method have been structurally characterized by an x-ray diffraction (XRD) study. Photoluminescence study of the developed phosphors under ultraviolet (UV) and near infrared (NIR) excitation has been performed. The excitation spectrum of the tetragonal zircon type YVO4 phosphors corresponding to the emission at ∼476 nm exhibits a broad excitation peak in the 250–350 nm region, which is due to charge distribution in the group. Under 980 nm CW diode laser excitation, enhancements of about ∼3000 times and ∼40 times have been observed for the blue band in the tridoped Tm3+Yb3+Zn2+:YVO4 phosphors compared to those of the Tm3+:YVO4 singly and Tm3+/Yb3+:YVO4 codoped phosphors, respectively. A downconversion (DC) emission study shows an enhancement of about ∼50 times for the blue band in the tridoped phosphors compared to that of the singly doped phosphors. Optical bistability (OB) behavior of the developed phosphors has been also investigated upon 980 nm excitation. The calculated Commission Internationale de l’Éclairage (CIE) color coordinates lie in the blue region with 96.5% color purity under 980 nm excitation, having a color temperature of ∼3400 K. Our observations show that the developed phosphors may be suitably used in dual mode luminescence spectroscopy, display devices, and UV LED chips.

Frequency upconversion and fluorescence intensity ratio method in Yb3+-ion-sensitized Gd2O3:Er3+-Eu3+ phosphors for display and temperature sensing

Near infrared (NIR) to visible frequency upconversion emission studies in Er3+-Eu3+/Er3+-Eu3+-Yb3+ co-doped/tri-doped Gd2O3 phosphors prepared by the co-precipitation technique have been explored under 980 nm laser diode radiation. The developed phosphors were characterized with the help of XRD, FE-SEM and FTIR analysis. No upconversion (UC) emission was found in the Eu3+-doped Gd2O3 phosphor. UC emission from Eu3+ ions along with Er3+ ions was observed in Er3+-Eu3+ and Er3+-Eu3+-Yb3+ co-doped/tri-doped phosphors. The UC emission arising from the Er3+ and Eu3+ ions was enhanced several times due to the incorporation of Yb3+ ions. The processes involved in the UC emission were obtained on the basis of the effect of energy transfer/sensitization through the Yb3+ → Er3+ → Eu3+ process. The red/green intensity ratio was improved from 0.16 to 1.50 and 1.01 to 1.50 for Er3+-Eu3+-Yb3+ tri-doped phosphors as compared to the Er3+-doped and Er3+-Yb3+ co-doped phosphors, respectively, at a fixed pump power density. A UC fluorescence intensity ratio (FIR)-based temperature sensing study was performed in the prepared Er3+-Eu3+-Yb3+ tri-doped Gd2O3 phosphors for green upconversion emission bands in the 300 K–443 K temperature range. A maximum sensor sensitivity of about ∼0.0043 K−1 at 300 K was achieved for the synthesized tri-doped phosphors upon excitation with a 980 nm laser diode. The colour coordinates lying in the green–yellow region are invariant, with variation in pump power density and temperature. The observed results support the utility of the prepared tri-doped phosphors in optical temperature sensing, display devices and NIR to visible upconverters.

Luminescent properties of single-phase Ba2-x-1.5y-1.5z P2 O7 :xEu2+ ,yCe3+ , zTb3+ phosphors for white light-emitting diode.

A series of Ba2 P2 O7 :xEu2+ ,yCe3+ ,zTb3+ phosphors was synthesized via a co-precipitation method, then their crystal structure, quantum efficiency and luminescent properties were analyzed by XRD and FL, respectively. The results showed that these phosphors not only presented the excitation characteristics of Ba2 P2 O7 :xEu2+ ,zTb3+ , but also exhibited that of the Ba2 P2 O7 :yCe3+ ,zTb3+ phosphor. Meanwhile, the tri-doped phosphor showed a stronger absorption around 320 nm in contrast with the Eu2+ /Ce3+ :Tb3+ co-doped phosphor. Not only can energy transfer from Ce3+ →Eu2+ be observed; the energy transfer mechanism from Eu2+ to Tb3+ is discussed in the tri-doped system. Ce3+ affects the luminescence properties of Ba2 P2 O7 :xEu2+ ,yCe3+ ,zTb3+ phosphors just as the sensitizer whereas Eu2+ is considered both as the sensitizer and the activator. The chromaticity coordinates of tri-doped phosphors excited at 320 nm stayed steadily in the bluish-white light region,and the emitted color and color temperature (CCT) of these phosphors could be tuned by adjusting the relative contents of Eu2+ , Ce3+ and Tb3+ . Hence, the single phase Ba2 P2 O7 :xEu2+ ,yCe3+ ,zTb3+ phosphors may be considered as potential candidates for white light-emitting diodes.

980 nm excited Er3+/Yb3+/Li+/Ba2+: NaZnPO4 upconverting phosphors in optical thermometry

The crystalline phase and optical properties of the NaZnPO4: Er3+/Yb3+/M (Li+/Ba2+) phosphors synthesized by conventional solid state reaction method, have been characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), Raman spectra, Diffuse reflectance spectra and Photoluminescence spectra. The effect of co-doping with Yb3+ and non-lanthanide ions (Li+ and Ba2+) on the upconversion (UC) emission intensity has been investigated. The enhancement of about ~ 52 and ~ 132 times respectively in green and red emission bands has been found in the NaZnPO4: Er3+/Yb3+/Li+ phosphors compared to that of the NaZnPO4: Er3+ phosphors. The green colour emitted from the tri-doped phosphors show colour purity ~ 97%. No colour tuning with variation of pump power density in the developed phosphors has been reported. The overall UC emission intensity of the green band of tri-doped phosphors performed in water at ~ 4.0cm of penetration depth reduces to ~ 66% of its original value in the powder phosphors. The maximum sensor sensitivity of the Er3+- Yb3+- Li+ and Er3+- Yb3+- Ba2+ tri-doped phosphors have been obtained as ~ 6.46×10−3K−1 at 603K and ~ 4.32×10−3K−1 at 523K respectively.

Near infrared to blue upconverting Tm3+/Yb3+/Li+:Gd2(MoO4)3 phosphors for light emitting display devices

Tm3+-Yb3+/Tm3+-Yb3+_Li+ codoped/tridoped Gd2(MoO4)3 phosphors using chemical co-precipitation method have been synthesized and characterised by XRD, FTIR, diffuse reflectance spectra and FE-SEM analysis. The downconversion emission spectra recorded by using 390nm radiation shows blue colour emission band due to the 1G4→3H6 transition of Tm3+ ion. Frequency upconversion emission study show overall intense blue, red and NIR upconversion emission bands due to the 1G4→3H6, 1G4→3F4 and 3H4→3H6 transitions of Tm3+ ion under 980nm laser diode excitation. The effect of incorporation of Li+ ions in the codoped phosphors produces small shifting in the XRD peaks towards the higher diffraction angle side and also intensity of the blue upconversion emission bands is enhanced around ∼510 times in the Tm3+-Yb3+_Li+:Gd2(MoO4)3 phosphors as compared to the Tm3+ doped phosphors. The confirmation of overall blue colour emission has been identified by colour co-ordinate analysis. The result shows that the developed tri-doped phosphors show improved blue colour emission and hence could be a proper material for near infrared to blue upconverter and blue colour emitting device fabrications.

Er3+-Tm3+-Yb3+ tri-doped CaMoO4 upconverting phosphors in optical devices applications

The structural and optical properties of the Er3+-Tm3+-Yb3+codoped CaMoO4 phosphors prepared by chemical route have been explored. The crystalline structures of the prepared phosphors have been investigated with the help of X-ray diffraction analysis. The presence of different vibrational modes and absorption bands arising due to the transitions from the ground state to different excited states of rare earth ions have been identified using the Raman and UV-VIS-NIR absorption spectra of the developed phosphor, respectively. The concentration quenching effect on the luminescence property of the prepared materials has been explained in detail. The upconversion luminescence property of the Er3+-Tm3+-Yb3+codoped CaMoO4 phosphor annealed at different temperatures under 980 nm and 808 nm excitations have been reported. The energy transfer Er3+ → Tm3+, Yb3+ → Er3+ and Tm3+ has been found to be responsible for efficient UC emission. The dipole-dipole interaction is observed to be responsible for the concentration quenching of the luminescence intensity. The effect of annealing temperature on the upconversion luminescence property has been explained in detail. The results suggest that the developed tri-doped phosphor may be suitable in making the efficient NIR to visible upconverter and lighting based optical devices.

Luminescent properties and energy transfer studies of color-tunable LuBO3: Ce3+/Tb3+/Eu3+ phosphors

A series of LuBO3: Ce3+/Tb3+/Eu3+ phosphors were synthesized via solid state reaction. The Ce3+/Tb3+ co-doped and Ce3+/Tb3+/Eu3+ tri-doped phosphors absorb near UV light through 4f-5d transitions of Ce3+, followed by sensitized Tb3+ green and Eu3+ red emission. Decay curves investigations for samples with various Tb3+ and Eu3+ contents reveal the occurrence of Ce3+→Tb3+→Eu3+ energy transfer. It is found that due to relative low Tb3+→Eu3+ energy transfer rate, a high Tb3+ content (>40%) is required for efficient Ce3+→Tb3+→Eu3+ energy transfer. Emission color of LuBO3: Ce3+, Tb3+, Eu3+ varies from blue through green to red with Ce3+/Tb3+/Eu3+ ratio. The quantum efficiency of LuBO3: Ce3+, Tb3+ green phosphor and LuBO3: Ce3+, Tb3+, Eu3+ red phosphor is 50% and 30%, respectively. Green and red LED prototypes were fabricated. The results show that the obtained phosphors are potential candidates as down-converted phosphors for NUV LEDs.

Long-wave UVA radiation excited warm white-light emitting NaGdTiO4: Tm3+/Dy3+/Eu3+ ions tri-doped phosphors: Synthesis, energy transfer and color tunable properties

NaGdTiO4 (NGT) phosphors doped with different activator ions (Tm3+, Dy3+, and Eu3+) were synthesized by a conventional solid-state reaction method in an ambient atmosphere. These phosphors were characterized by scanning electron microscope images, transmission electron microscope images, X-ray diffraction patterns, Fourier transform infrared spectra, and photoluminescence spectra. All the samples were crystallized in an orthorhombic phase with a space group of Pbcm (57). In Tm3+/Dy3+ ions co-doped samples, white-light emission was observed under near-ultraviolet (NUV) excitation. In addition, the energy transfer between Tm3+ and Dy3+ ions was proved to be a resonant type via an electric dipole–dipole mechanism and the critical distance of energy transfer was calculated to be 19.91 Å. Furthermore, Tm3+/Dy3+/Eu3+ ions tri-doped NGT phosphors demonstrated warm white-light emission by appropriately tuning the activator content, based on the principle of energy transfer. These NUV wavelength excitable phosphors exhibit great potential as a single-phase full-color emitting phosphor for white light-emitting diode applications.

Pump power induced tunable upconversion emissions from Er3+/Tm3+/Yb3+ions tri-doped SrY2O4nanocrystalline phosphors

RE3+ (Er3+/Tm3+/Yb3+) ions tri-doped SrY2O4 nanocrystalline phosphors were synthesized by a citrate sol–gel method. After annealing at 1300 °C, the structure was identified to be pure orthorhombic and the particles were found to be nearly spherical in shape. The up-conversion emission spectra of the SrY2O4:1Er3+ phosphor revealed a bright green emission (4S3/2 → 4I15/2) around 551 nm. To enhance the red emission of the Er3+ ions, Yb3+ ions were co-doped with Er3+ ions, leading to a greenish yellow emission under 980 nm excitation. In the case of the 1Er3+/1Tm3+/3Yb3+ ions tri-doped phosphor, white-light emission was observed corresponding to the 1G4 → 3H6 (Tm3+), 4S3/2 → 4I15/2 (Er3+) and 4F9/2 → 4I15/2 (Er3+) transitions at 487, 551 and 664 nm, respectively. It was interestingly noticed that, when the exciting pump power was changed from 100 to 900 mW, the blue emission band of the Tm3+ ions was enhanced by the suppression of the red and green emission bands of the Er3+ ions so that the chromaticity coordinates were also moved to the cyan emission region. This feature suggests that the Er3+ ion may also act as a sensitizer for the Tm3+ and Yb3+ ions and a possible energy transfer mechanism was also discussed.