Synthesis And Spectral Properties Of Novel Rare Earth Ions Doped Luminescent Materials For White LEDs

White-light emitting diodes（W-LEDs）have gradually replaced traditional incandescent lamps and fluorescent lamps for ordinary lighting in daily life because of their energy saving and environmental protection requirements.Among the common types of W-LEDs,luminescent material conversion W-LED（pc-WLED）has occupied the mainstream market due to its high luminous efficiency,low cost,simple structure and high spectral design.However,the luminescent materials currently used for manufacturing W-LEDs have many disadvantages,such as low color rendering index,high color temperature,and unstable luminescence.Therefore,it is becoming more and more important to study various new luminescent materials for W-LEDs.In this paper,a series of luminescent materials with different luminescent colors were synthesized by conventional high temperature solid phase method,and their different spectral properties were explored.The specific research contents are as follows:1.A series of NaLaMgWO₆:Dy³⁺、NaLaMgWO₆:Er³⁺、NaLaMgWO₆:Sm³⁺、NaLaMgWO₆:Pr³⁺phosphors were prepared by a conventional solid-state reaction method at high temperature.The phase structure,morphology,particle size distribution and concentration dependent luminescence properties of the phosphors were investigated for the first time.Upon excitation with UV（290 nm）and n-UV（388 nm）,NaLaMgWO₆:Dy³⁺phosphor exhibited typical Dy³⁺emission corresponding to the ⁴F_9/2-⁶H_J（J=15/2,13/2,11/2）transitions of Dy³⁺,in which the hypersensitive electronic dipole transition ⁴F_9/2-⁶H_13/2（575 nm）was with strongest emission intensity leading to the yellow emission with the CIE chromaticity coordinates（0.441,0.475）.The optimal concentration of Dy³⁺was found to be8%.The luminescence decay lifetime for ⁴G_5/2-⁶H_13/23/2 transition of Dy³⁺was of millisecond level and decreased with the increase in Dy³⁺ion concentration.The obtained results indicated that NaLaMgWO₆:Dy³⁺phosphor could be a potential yellow emitting phosphor for possible application in w-LEDs.Upon excitation with near ultraviolet（379 nm）,the as-prepared NaLaMgWO₆:Er³⁺phosphors exhibited the dominated green emissions,in which the ⁴S_3/2-⁴I_15/2 transition（544 nm）was with the highest intensity.The optimal concentration of Er³⁺was confirmed to be 0.03,beyond which the concentration quenching phenomenon of Er³⁺occurred due to the electric dipole–dipole interaction between the neighboring Er³⁺ions.The decay lifetime for ⁴S_3/2→⁴I_15/2 transition of Er³⁺was of microsecond level and decreased monotonously with the increasing Er³⁺ion concentration.The alkali metal ion substitution strategy was also utilized to improve the green emissions of NaLaMgWO₆:Er³⁺phosphor by replacing Na⁺with K⁺/Li⁺.This present work is helpful for the development of novel green-emitting phosphors for the potential application in white light-emitting diodes.The crystal structure,phase purity,morphology,particle size distribution as well as elemental composition of the as-prepared phosphors were investigated carefully with the aid of XRD,SEM,EDS,FT-IR analyses,indicating the high-purity and micron-sized NaLaMgWO₆:Sm³⁺phosphors with monoclinic structure were prepared successfully.The spectroscopic properties of Sm³⁺in NaLaMgWO₆ host including UV–vis diffuse reflection spectrum,photoluminescence excitation and emission spectra,decay curves,chromaticity coordinates and internal quantum efficiency were investigated in detail.Upon excitation with UV（290 nm）and n-UV（406 nm）,NaLaMgWO6:Sm³⁺phosphor presented red emission corresponding to the ⁴G_5/2-⁶H_J（J=5/2,7/2,9/2,and 11/2）transitions of Sm³⁺,in which the hypersensitive electronic dipole transition ⁴G_5/2-⁶H_9/2（645nm）was with the strongest emission intensity because Sm3+ions were located at a lattice site with anti-inversion symmetry.The optimal concentration of Sm3+was different for the given excitation wavelength such as 290 nm and 406 nm,which was interpreted by the extra effect of the energy transfer from W⁶⁺-O^2-group to Sm³⁺.The decay lifetime for ⁴G_5/2-⁶H_9/2transition of Sm³⁺was very short（<1 ms）and decreased with the increasing Sm³⁺concentration.The present investigation indicates that NaLaMgWO₆:Sm³⁺phosphor could be a potential red component for application in w-LEDs.The excitation spectrum consists of a host-related excitation band（250–350 nm）and some f-f transition bands of Pr³⁺（440–500 nm）,in which the latter ones can match well with the commercially available blue-emitting LED chip.Upon excitation with UV（²68 nm）and blue light（⁴51 nm）,the as-prepared phosphors exhibit red emission originating in the transitions from ³P₀ state of Pr³⁺,in which the transition of ³P₀→³F₂（⁶54 nm）is dominant.The optimal concentration of Pr³⁺is confirmed to be 7%,beyond which the d-d interaction plays an important role in the concentration quenching phenomenon of Pr³⁺.Furthermore,the luminescence decay lifetime for ³P₀→³F₂ transition of Pr³⁺is of microsecond level and decreases with the increase in Pr³⁺ion concentration.Finally,a white LED device is fabricated with the combination of phosphors(YAG:Ce³⁺+NaLaMgWO₆:Pr³⁺)and commercial blue-emitting LED chip to explore preliminarily the potential application of NaLaMgWO₆:Pr³⁺red phosphor in solid state lighting field.2.A series of novel Ce³⁺singly doped and Ce³⁺,Tb³⁺co-doped Ba₃P₄O₁₃ phosphors[Ba₃P₄O₁₃:Ce³⁺,Ba₃P₄O₁₃:Ce³⁺,Tb³⁺]were synthesized via the high-temperature solid-state reaction method.The photoluminescence properties and energy transfer behavior of the as-prepared phosphors were investigated in detail.The Ba₃P₄O₁₃:Ce³⁺phosphors produced broadband emission ranging from 300 to 400 nm upon UV excitation.The optimal concentration of Ce³⁺and critical distance for Ce³⁺-Ce³⁺energy transfer was ascertained by investigating the concentration dependent luminescence properties of Ce³⁺in Ba₃P₄O₁₃host.The Ce³⁺-Tb³⁺energy transfer phenomenon was proved to exist in the Ba₃P₄O₁₃:Ce³⁺,Tb³⁺phosphors,which led to the broadband sensitized yellowish-green emission of Ba₃P₄O₁₃:Ce³⁺,Tb³⁺phosphors upon UV excitation.The efficiency and mechanism of Ce³⁺-Tb³⁺energy transfer was also investigated by theoretical calculation.3.Thedevelopmentofnear-ultraviolet（n-UV）-excitablesingle-phase white-light-emitting phosphor is highly meaningful for phosphor-converted white light-emitting-diodes（pc-WLEDs）based on n-UV chips.In this work,a series of Dy³⁺singly doped and Ce³⁺,Dy³⁺co-doped KBaY（BO₃）₂ phosphors with different doping concentration of Ce³⁺/Dy³⁺were designed and synthesized via a solid state reaction at high temperature,and their phase structure,photoluminescence properties and potential application in WLEDs were investigated in detail.The prominent sensitization effect of Ce³⁺on Dy³⁺-luminescence based on Ce³⁺-Dy³⁺energy transfer is authenticated by comparatively investigating the photoluminescence excitation and emission spectra of the asprepared phosphors.The critical distance,efficiency,and mechanism of Ce³⁺-Dy³⁺energy transfer are calculated and determined in term of the theoretical formulas.The n-UV-excitable white light emission is realized in the KBaY（BO₃）₂:Ce³⁺,Dy³⁺phosphors with the appropriate doping concentration of Ce³⁺and Dy³⁺ions.A pc-WLEDs device is successfully fabricated by the combination of the single-phase KBaY（BO₃）₂:Ce³⁺,Dy³⁺phosphor and an n-UV（³65 nm）LED chip.All these properties indicate that the developed single-phase KBaY（BO₃）₂:Ce³⁺,Dy³⁺phosphor may have potential application prospect for pc-WLEDs.