Preparation And Spectral Properties Of Narrow-band Red Phosphors For W-LED

With the rapid development of science and technology,lighting equipment is also improving.Photoelectric conversion efficiency is gradually improving from incandescent lamp to light emitting diode?LED?.White light-emitting diodes?w-LEDs?have received much more attention since w-LEDs provide extraodinary surperiorities,such as environmental friendiness,high brightness,high luminous efficiency and long life.So far,there are two ways putting into commercial production:?1?Combining blue-emitting InGaN/GaN-based LED chips and yellow-emitting YAG:Ce³⁺(Y₃Al₅O₁₂:Ce³⁺)to make white light emission;?2?Employing near ultraviolet emitting LED chips coated with trichromatic phosphors to prepare white LEDs.In these two method,phosphors are the core components of LED devices.Using phosphors conbine with LED chips is a relatively simple and cheap way to synthetise white light.In order to fabricate white LEDs with high brightness,environmental-friendly,energy saving and high luminous efficiency,we need to develop high quality phosphors.The disadvantage of the first method is absence effective red light components,which leads to poor color rendering and color temperature of phosphors?Ra<80,CCT>4000K?.Eu³⁺,Eu²⁺usually are the most commonly used activators of red phosphors at present.The price of Eu₂O₃ is relatively cheap in rare earth ion,however,they need use high temperature solid-phase method with high cost.To solve the problem,we need to prepare a kind of red phosphor which can be synthetized in low temperature environment and non-rare earth compounds as materials.There are some shortcomings in the second way,including fluorescence reabsorption between different components and non-uniformity of the luminescence properties,which reduces the overall luminescence efficiency.Therefore,a single-phased phosphors for NUV pumped w-LED is the best way to replace the three basic phosphors.Based on the above two schemes,we try to synthesize kinds of red phosphor with low-cost and high-efficiency.Another more,preparing single-phased phosphors which can be stimulated by NUV LED and the experimental results are as follows:?1?The red phosphors Ba₂ZrF₈:Mn⁴⁺was synthesized by two-step methord.The effects of concentration of doping concentration and the ratio of reactants on the luminescent properties,crystal structure and morphology of the phosphors have been investigated in detail.The experimental results show that as-prepared phosphors are composed of a number of irregular particles with smooth surfaces,clear edges,and the shape is rodlike.Different Mn⁴⁺doping concentration has light effect on the morphology and size of the product.The change of reactant proportion will not seriously affect the lattice,but will change the luminescence intensity.The chromaticity coordinates?CIE?of the Ba₂ZrF₈:Mn⁴⁺are calculated to be x=0.68,y=0.32,which are concentrated in the red-light region,exhibiting high color purity.?2?The red emitting phosphors CsNaGeF₆:Mn⁴⁺were fabricated by two-step methord.The crystal structure of CsNaGeF₆:Mn⁴⁺is similar to CsNa(Ge_0.5Sn_0.5)F₆ by comparing with standard card,which may also belong to space group pbcm.The obtained products exhibit rod-shaped with regular morphology,smooth surfaces and clear edge.The average size of the crystal is about 2?m which is in the range of commercial applications?1⁵?m?.The substrate has a wide band gap of 0.52 eV,which can be used for rare earth luminescent materials.The concentration quenching of CsNaGeF₆:Mn⁴⁺red phosphors energy transfer mechanism was occurred via dipole-dipole interaction.The thermal stability of the sample is was investigated via a temperature-dependent luminescence experiment.The luminous intensity of CsNaGeF₆:Mn⁴⁺drops by 50%at 150?after comparing with the intensity at room temperature.What's more,the emission intensity has little change with temperature.According to Arrhenius formula,the activation energy is calculated to be?E=0.69eV,which is suitble used for rare earth doped phosphors.?3?The phosphors of NaY₉?SiO₄?₆O₂:Bi³⁺,Eu³⁺was prepared by high temperature solid-state method.The effects of Bi³⁺,Eu³⁺doping concentration,excitation wavelength and temperature on the luminescence properties,crystal structure,morphology,PL and PLE spectrum of phosphors were studied.The results show that the characteristic peaks also be changed under the different excitation wavelenths from 335-370 nm.With the increase of excitation wavelength,the intensity of emission phonon-assisted with peak at⁵06 nm gradually weakened,meanwhile,the peak at⁴10 nm gradually increased,which indicates that there are at least two kinds of Bi³⁺luminescent centers in NYSO host.It is possible to control the emission color by energy transfer between Bi³⁺,Eu³⁺and the changing of excitation wavelength.According to the temperature-dependent emissions,there have some differences in Bi???and Bi???centers,from which we infer that the energy tansfer efficiency between two centers may be for phonon-assisted process.The luminous intensity of NYSO:Bi³⁺,Eu³⁺at T₁₅₀?still about 78%while comparing with that at T₂₅?,which can meet the needs of application.