Luminescence Properties Tuning Of Self-activated Monoclinic Lu_2-xLn_xWO₆?Ln=Sm,Yb?

Under long wave ultraviolet light excitation,self-activated monoclinic tungstate lutetium?Lu₂WO₆?showed broad band emission spectrum almost covering the whole visible light regions.However,the red light emission intensity was weaker.In this paper,the research status of monoclinic lutetium tungstate was analyzed.The luminescence mechanism and performance regulation of samarium?Sm?and ytterbium?Yb?doping monoclinic Lu₂WO₆was systematically explored by combining the first-principle calculation and experiment synthesis.Through ground state and constrained density function calculations,Sm³⁺ions luminescence in self-activated monoclinic Lu₂WO₆ was originated from intra 4f?4f transitions,not inter 5d?4f transitions.Theoretically the white luminescence was obtained by combining red and blue green emissions of 4f?4f energy levels and W-O charge transfer transitions.Experimentally,pure and Sm³⁺doping Lu₂WO₆ powders were synthesized using solid phase reaction calcined in air atmosphere.By the analysis of X-ray photoelectron spectroscopy and Rietveld refinement,element Sm charge state was trivalent,and Sm³⁺doping was concentration dependent selectively doping in three Lu sites.With the increment of Sm³⁺concentrations,the color coordinates changed gradually from blue through white light toward orange in the visible spectral upon 325 nm excitation.On the basis of the theoretical prediction and experimental preparation,a white emission light emission diode lamp was produced using a 365 nm ultraviolet chip and Lu_1.99Sm_0.01WO₆ phosphor.A series of monoclinic Lu₂WO₆:xYb³⁺samples were synthesized by high temperature chemical reaction.Upon ultraviolet 300 nm excitation,all doping samples showed 900-1200nm near infrared emission,corresponding to the three degenerate ²F_5/2 states to four degenerate ²F_7/2 state transitions.The prepared samples were pure phase and single crystal particles by the analysis of X-ray diffraction and transmission electron microscopy.In any doping concentration,Yb³⁺simultaneously occupied three Lu sites and the host band gaps values was almost unchanged from Rietveld refinement and diffuse reflectance spectra.X ray photoelectron spectroscopy and energy dispersive spectroscopy indicate that Yb³⁺charge state was positive trivalent and Yb content increased gradually,in consistency with reality.From the visible fluorescence decay spectra,energy transmission between tungstate group and Yb³⁺was one-step energy transfer process.Lu₂WO₆:xYb³⁺near infrared emission can be used to improve utilization efficiency of sunlight for crystal silicon solar cell.