Research On New High-brightness Phosphors Applied To WLED

Phosphors doped with rare earth have excellent luminescence characteristics and wide wavelength coverage,and its have significant applications in many fields,such as display,LED lighting,temperature sensor,biological probe,and so on.Especially in recent years,the investigations on the design and synthesis of red and green phosphors doped with rare earth for WLEDs,as well as the analysis of photoluminescence characteristics and mechanism,have becoming one of the new hot topics.In this thesis,the preparation technology and photoluminescence characteristics of two series of novel nanophosphors,that is,Li_ySr_4-1.5xEu_x(Mo O₄)_2y-7and LiLa(WO₄)₂:Tb³⁺,are mainly discussed.The concrete works are as follows:(1)Two series of nanophosphors,including Li_ySr_4-1.5xEu_x(Mo O₄)_2y-7and LiLa(WO₄)₂:Tb³⁺,have been synthesized by high-temperature solid-phase reaction method,and the preparation process and parameters are optimized.At the same time,the influence of Li⁺,Eu³⁺and Tb³⁺ions on the crystal structure of the phosphor is analyzed with X-ray diffractometer.The results indicate that the unit cell volume of phosphor becomes smaller slightly and the growth orientation of the particle crystal gets changed slightly when the rare earth ions are doped;The scanning electron microscope images show that the phosphor particles still remain ellipsoidal or spherical after incorporating Eu³⁺and Tb³⁺,however,the average size becomes smaller with the increasing of activated ion concentration.(2)The photoluminescence characteristics of Li_ySr_4-1.5xEu_x(Mo O₄)_2y-7nanophosphor are focused to research.When 617 nm is selected as the monitoring wavelength,the excitation spectrum shows that there exist six peaks,among which the two excitation peaks of 396 nm near ultraviolet and 466 nm blue light are very strong.Therefore,396 and 466 nm are chose as the excitation wavelengths,respectively,and intense red light at 617 nm emitting from the phosphors and it originates from the transition between the⁵D₀and⁷F₂energy levels of the trivalent europium ion have been obtained.The CIE coordinates are(0.663,0.320)and(0.672,0.327)respectively,which are close to standard red light.Then,the variation of the luminous intensity of Sr_4-1.5xEu_x(Mo O₄)₄phosphor with the concentration ratio of europium and strontium is also studied,and the optimized concentration ratio is Eu:Sr=1.8:1.3;The influence of Li⁺concentration on the emission spectrum of Sr_4-1.5xEu_x(Mo O₄)₄phosphor is further analyzed and the optimized lithium doping concentration is 2 mol%.(3)The excitation spectra and emission spectra of LiLa(WO₄)₂:Tb³⁺green phosphor are systematically discussed.When the monitoring wavelength is set to 546 nm,there are two absorption bands in the ultraviolet and blue regions,of which the near-ultraviolet excitation peak at 379 nm is the strongest,followed by the blue excitation peak at 489 nm.LiLa(WO₄)₂:Tb³⁺nanophosphor can emit strong 546 nm green light,which belongs to the transition between the ⁵D₄and ⁷F₆energy levels of the trivalent terbium ion.Under the excitations of379 and 489 nm,the optimized doping terbium concentration is 0.3 mol%.In addition,the impact of alkali metal ions Li⁺and K⁺on the luminescence performance of terbium-doped phosphors is also analyzed.It is found that the photoluminescence intensity of the former is significantly better than that of the latter.The internal mechanism is attributed to the difference in the radius of alkali metal ions,which affects the the polarization between chemical bonds and results in large difference of luminous intensity.