White luminescence of Ho^(3+)/Tm^(3+)/Yb^(3+)-codoped CaWO_4 synthesized via citrate complex route assisted by microwave irradiation

The nanocrystalline Ho3+/Tm3+/Yb3+ co-doped CaWO4 upconversion(UC) phosphors were successfully synthesized by a modified citrate complex method using microwave irradiation. The citrate complex precursors were heat-treated at temperature ranging from 300 to 700 °C for 3 h. Crystallization of the Ho3+/Tm3+/Yb3+ co-doped CaWO4 was detected at 400 °C, and entirely completed at 600 °C. The Ho3+/Tm3+/Yb3+ co-doped CaWO4 heat-treated at 600 °C showed primarily spherical and homogeneous morphology. Under the laser excitation of 980 nm, Ho3+/Tm3+/Yb3+ co-doped CaWO4 shows the bright white upconversion(UC) emission visible to the naked eye, which is composed of a blue emission at 475 nm from Tm3+, and green and red emissions at 543 and 651 nm respectively from Ho3+. The coordinates of Ho3+/Tm3+/Yb3+ co-doped CaWO4 in the Commission International De'eclairage(CIE) chromaticity diagram could be controlled from a cool to a warm white color depending on the Tm3+ and Ho3+ concentrations. The UC luminescent properties on Tm3+ and Ho3+ concentrations and related mechanism based on laser pump power were discussed in detail.

White up-conversion luminescence and highly-sensitive optical temperature sensing in Na_(3)La(VO_(4))_(2):Yb,Er,Tm,Ho phosphors

In this work,tunable white up-conversion luminescence was achieved in the Yb^(3+),Er^(3+),Tm^(3+),Ho^(3+) codoped Na_(3)La(VO_(4))_(2) phosphors under 980 nm excitation.The emissions of three primary colors are mainly attributed to the ~2H_(11/2)/~4S_(3/2)→~4I_(15/2) transitions of Er^(3+),~1G_(4)→~3H_6 transition of Tm^(3+),and_5F_5→~5I_8 transition of Ho^(3+).White luminescence characteristics and mechanisms of up-conversion system were investigated in detail.In addition,the temperature sensing behaviors of multiple levels emission combinations for Na_(3)La(VO_(4))_(2):Yb^(3+),Er^(3+),Tm^(3+),Ho^(3+) were analyzed by employing thermally coupled and non-thermally coupled energy levels.Based on the emissions of ~3F_(2,3)/~1G_(4) energy levels,the maximum relative and absolute sensitivities were obtained to be 2.20%/K and 0.279 K^(-1).The design of up-conversion luminescence materials with high-quality white luminescence and excellent sensitivity performance is critical in the field of optical applications.

White-light upconversion emission of lanthanide double-doped oxide nanoparticles via defect state luminescence of ZnO

The white upconversion luminescence （UCL） of upconversion nanoparticles （UCNPs） is mainly made up of the color red, green and blue. Interestingly, the white-light-emitting UCNPs can be obtained via a complex method of tridoping lanthanide ions such as Yb^3＋, Er^3＋, and Tm^3＋. We herein report that an excellent white UCL can be obtained from Yb/Tm double-doped ZnO. In this system, the blue and red UCL-emissions around 475 and 652 nm originate from ^1G4→^3H6 and ^1G4→^3F4 transition of Tm^3＋, respectively, and the green one can be attributed to the defect states （oxygen va- cancies） luminescence （DSL） of the ZnO host. Meanwhile, the fine nanostructure of ZnO：Yb/Tm is prepared by adjusting the concentration of OH-. Particularly, the one dimentional pencil-shaped nanorods with high aspect ratio achieve a strong green DSL emission due to the high concentration of oxygen vacancy. The oxygen vacancy defects play an irreplaceable role in affecting the intensities of blue and red UCL by acting as the intermediate state in the energy transfer process. More importantly, we demonstrate that the DSL and UCL can be combined into systems, paving a new road for obtaining the white UCL emission.

Tunable white-light emission of lanthanide(Ⅲ) hybrid material based on hectorite

In this work, we present novel trivalent lanthanide ions（Ln^3＋）-based luminescent hybrid materials, in which the organic ligands are covalently grafted on the hectorite templates and the Ln^3＋ ions can be well immobilized by the ligands through coordination bond. The hybrid materials exhibit tunable emission colors by varying the molar ratio of Eu^3＋ to Tb^3＋, and the one with Eu^3＋：Tb^3＋=1：1 exhibits excellent coordinate of（0.327, 0.328） located in the ＂white region＂ of the CIE 1931 chromaticity diagram（under300 nm UV illumination）. These properties make the hybrid composites suitable for fabricating optoelectronic devices such as full-color displays and white LED.

White light-emitting Ba0.05Sr0.95WO4:Tm3+Dy3+phosphors

Tm3＋ and Dy3＋） co-doped Ba（0.05）Sr0.95WO4 phosphors were synthesized by a low temperature combustion method. The structures of the samples were SrWO_4 phase and were identified by X-ray diffraction. The surface topographies of Ba_（0.05）Sr_（0.91）WO_4：0.01 Tm^（3＋） 0.03 Dy^（3＋） were tested by scanning electron microscopy. The particles are ellipsoid, and their average diameter is approximately 0.5 μm. The emission spectra of Ba_（0.05）Sr_（0.95）WO_4：Tm^（3＋） show a peak at 454 nm which belongs to the ~3 H_6→~1 D_2 transition of Tm^（3＋）, and the optimum doping concentration of Tm^（3＋） ions was 0.01. The emission spectra of Ba_（0.05）Sr_（0.95）WO_4：Dy^（3＋） consist of the ~4 F_（9/2）→~6 H_（13/2） dominant transition located at 573 nm, the weaker ~4 F_（9/_2→~6 H_（15/2） transition located at 478 and 485 nm. And the weakest ~4 F_（9/2）→~6 H_（11/2） transition located at660 nm, and the optimum doping concentration of Dy^（3＋） ions was 0.05. A white light is achieved from Tm^（3＋） and Dy^（3＋） co-doped Ba_（0.05）Sr_（0.95）MoO_4 crystals excited at 352-366 nm. With the doping concentration of Tm^（3＋） fixed at 0.01, the luminescence of Ba_（0.05）Sr_（0.95）MoO_4：Tm^（3＋）Dy^（3＋） is closest to standard white-light emissions when the concentration of Dy^（3＋） is 0.03; the chromaticity coordinates are（0.321,0.347）, and the color temperature is 6000 K.