Font Size: a A A

Preparation And Luminescence Of (Fluoro-) Phosphates And Alkaline Earth Aluminates Doped With Rare-Earth/Mn(â…£)

Posted on:2017-04-17Degree:DoctorType:Dissertation
Country:ChinaCandidate:L L MengFull Text:PDF
GTID:1221330485498306Subject:Chemical processes
Abstract/Summary:PDF Full Text Request
For the next-generation of solid-state lighting products, white light-emitting diodes (W-LEDs) have attracted substantial attentions owing to their superior characteristics such as lower voltage, extraordinary luminous efficiency, energy-saving capacity, durability and environmental friendliness. Phosphor-converted LED (PC-LED) is the mainstream technology to achieve white-emitting LEDs. For the purpose, desirable phosphors are needed to be efficient excited by blue or near UV(n-UV)LED chip and show high converting efficiency. A conventional W-LED using Y3A15O12:Ce3+(YAG:Ce3+) phosphors excited by an InGaN blue LED chip has a low color rendering index due to the lack of a red component in phosphors, which gives "cool"-white light. In order to generate white light with the warm perception similar to incandescent light, one of the best strategies is to mix a high efficient red phosphor into YAG:Ce3+ Therefore, it is of academic interesting and potential application to improve the excitation efficiency of traditional phosphors and search for new red emitting phosphors. The aim of this thesis is to improve the luminescence efficiency of (fluoro-) phosphates phosphors and search for red emitting alkaline earth aluminates phosphors. At the same time, the effects of the crystallization, particle morphology and charge compensation on the photoluminescence of phosphors were studied.Firstly, the definition and application of luminescent materials, especially WLED, were introduced. And then, the development status quo of Mn(â…£) doped phosphors and alkaline earth aluminates activated by rare-earth were presented. To overcome the defects and shortages of (oxy)fluoride phosphors activated by Mn(â…£), it is urgent to search for high efficient red emitting alkaline earth aluminates phosphors.The (fluoro-) phosphates and alkaline earth aluminates phosphors were synthesized by various methods, including combustion method, hydrothermal method, solid state method and hydrothermal homogenous precipitation method. The crystal structure and particle morphology of the resulting powder samples were characterized by X-ray diffraction and scanning electron microscopy. The diffuse reflectance spectra, photoluminescence (PL) emission and excitation spectra of the phosphors were also studied. Besides, the thermal decomposition of the hydrothermal homogenous precipitation precursor was studied by non-isothermal kinetics. The results of the investigation of all the phosphors were shown in the following:1. Ca10-xLi(PO4)7:xRE(RE=Eu3+,Dy3+) and Ca5.x(PO4)3F:xEu3+ phosphors were synthesized by combustion method. The quenching concentration of rare-earth ions in Ca10-xLi(PO4)7:xRE(RE=Eu3+, Dy3+) and the quenching concentration of Eu3+ in Ca5-x(PO4)3F:xEu3+ series were 10 mol% and 1 mol%, respectively. Ca5(PO4)3F and Sr5(PO4)3F were prepared by hydrothermal method. The morphology of Sr5(PO4)3F in ethanol was a regular rod-like shape, and it was spherical shape aggregated by nanorods in ethylene glycol or polyethylene glycol 400. The morphology of Sr5(PO4)3F:xRE(RE=Eu3+, Dy3+,Tb3+) was a regular rod-like shape, when they were prepared with sodium hydroxide to adjust pH, and it was hexagonal prism with potassium hydroxide. Sr5(PO4)3F:xRE(RE= Eu3+, Dy3+, Tb3+) prepared with sodium hydroxide had higher luminescence efficiency than that of Sr5(PO4)3F:xRE(RE=Eu3+, Dy3+, Tb3+) with potassium hydroxide.2. Sr4Al14O25 activated by Mn4+ and Sm3+ were synthesized by high-temperature solid state reaction technique. The effects of Mg2+, Ge4+, Li+, Na+ ions co-doping on the photoluminescence of phosphors were studied. Sr4Al13.99-xO25:0.01Mn4+,xMg2+(Ge4+) and Sr4-x/2Li(Na)xAl14-0.01×4/3Mn0.01O25 had broad absorption band in the range of 250~500 nm, which matches well with the blue or n-UV LED chip. The emission spectra of the phosphors presented a double-peak structure between 600 nm and 700 nm with the strongest band at about 654 nm. Compared with Sr4Al13.99O25:0.01Mn4+, the strongest emission intensity of Sr4Al13.98O25:0.01Mn4+,0.01Mg2+ and Sr4Al13.97O25:0.01Mn4+,0.02Ge4+ increased by 175% and 60%, respectively. The photoluminescence of Sr4-x/2NaxAl14-0.01×4/3Mn0.01O25 was superior to that of Sr4-x/2LixAl14-0.01×4/3Mn0.01O25, and the optimum concentrations of Na+ and Li+ were 5 mol%. Compared with Sr4Al14.0.01×4/3Mn0.01O25, the maximum emission intensities of Sr4-0.05/2Na0.05Al14-0.01×4/3Mn0.01O25 and 025 increased to 260% and 190%, respectively. The excitation spectra of Sr4-xAl14O25:xSm3+ and Sr4-2XAl14O25:xSm3+,xNa+ in the range of 330~500 nm were due to f-f transition of Sm3+ion. The highest intensity peak located at 400 nm, which was attributed to6H5/2â†'5P3/2 transition. Meanwhile, the phosphors presented orange-light emission of Sm3+ under 400nm light excitation, and highest intensity peak was located at 598 nm (4G5/2â†'6H7/2). The photoluminescence of Sr4-2XAl14O25:xSm3+, xNa+ was superior to that of Sr4-xAl14O25:xSm3+, which was explained by charge compensation theory, and the optimum concentrations of Sm3+ and Na+ were 3 mol%.3. Sr2MgAl22O36:Sm3+, Sr2MgAl22O36:Mn4+ and SrMgAl10O17:Mn4+ were obtained by high-temperature solid state reaction. The phosphors presented orange-light emission of Sm3+ and red-light emission of Mn4+, respectively. The quenching concentration of Sm3+ in Sr2-2xSmxMx(M=Li, Na)MgAl22O3 was 5 mol%. Co-doping of Li+ and Na+ ions enhanced the photoluminescence of Sr2MgAl22-0.01×4/3Mn0.01O36, and the optimum concentrations of Na+ and Li+ were 4 mol%. The quenching concentration of Mn4+ in SrMgAl10-xO17:xMn4+ was 1.5 mol%, and the effects of co-doping ions (Li+, Na+, K+, Cl-, Ge4+) on photoluminescence of SrMgAl10O17:Mn4+ were different.4. Mn4+ and Eu3+ doped CaAl12O19 were synthesized by hydrothermal homogenous precipitation method. The preparation procession, particle morphology and photoluminescence were investigated. At the same time, the thermal decomposition of the precursor of CaAl12O19:Mn4+ was studied by non-isothermal kinetics. CaAl12O19:Mn4+ and CaAl12O19:Eu3+ presented red-light emission of Mn4+ and orange-light emission of Sm3+, respectively. They had a flake-like morphology. The average value of activation energy Ea associated with the thermal decomposition of the precursor of CaAl12O19:Mn4+ was 140.46 KJ·mol-1, obtained using OFW and KAS methods. The most probable mechanism function g(a) with integral form (g(α)=(1-a-4.59)-1) was deduced by Masterplots method, which belonged to the mechanism of chemical reaction. Besides, the pre-exponential factor A (3.47×1012s-1) and the thermodynamic parameters (â–³S#=-19.21 J·mol-1,â–³H=135.33 KJ·mol-1, and â–³G#=147.17 KJ·mol-1) of the thermal decomposition of the precursor were determined.
Keywords/Search Tags:Phosphor, Luminescence properties, (Fluoro-)Phosphates, Alkaline earth aluminates, Non-isothermal kinetics
PDF Full Text Request
Related items