| As a new concept of new solid-state light source, white light emitting diodes(LEDs) are opening a new revolution in human lighting field, because of their long life, high energy saving, environmental protection and other significant characteristics. At present, the mainstream white LED in market is phosphor convert LED(abbreviated pc-LED), wherein the luminescent material as an important part, and its performance directly affects the performance of white LED devices, which has received extensive attention. Generally, there are two ways can be employed to get white light: one is using yellow phosphor YAG:Ce3+ to convert blue light ships to obtain white light; the other is using three phosphors colored as blue, green and red, to convert ultraviolet light into white light. Aiming at the existed problems of phosphors for(near) UV LEDs, in this thesis, through designing and exploring the synthesis of materials, crystal structure refinement and spectral characterization, we systematically investigated the synthesis and luminescence properties of several new blue, green and white light emission phosphors. The main research contents are as follows: 1. A double substitution induced blue-emitting phosphor Ca(Mg0.8, Al0.2)(Si1.8, Al0.2)O6:Eu2+(CMAS:Eu2+) was successfully synthesized by solid-state reaction process, the structure and luminescence properties were investigated in detail. The crystal structure and chemical composition of CMAS matrix was analyzed and determined based on Rietveld refinements and Energy Dispersive Spectroscopy(EDS) spectrum. The composition-optimized CMAS:Eu2+ exhibited a strong blue light, centered at 446 nm upon excitation at 365 nm with the Commission Internationale de L’Eclairage(CIE) coordinates of(0.144, 0.113). Under 380 nm excitation, the PL emission intensity area of the optimized phosphor was found to be 46.95% of that of a commercial BaMgAl10O17:Eu2+(BAM:Eu2+) phosphor and the quantum efficiency of the phosphor is 41.32%. The temperature-dependent PL studies have been investigated which shows the thermal stability of CMAS:Eu2+ phosphor compared with that of CaMgSi2O6:Eu2+(CMS: Eu2+) phosphor. 2. Divalent europium-doped alkaline earth metal silicate phosphors Ba9Lu2Si6O24 have been successfully prepared by solid-state reaction. The analysis of X-ray diffraction shows that the compounds are in a single phase and the Rietveld refinements show that the lattice parameters are a = b = 9.98834(16) ?, c = 22.1010(4) ?. Under the excitation of 380 nm, the PL emission was centered at around 505 nm, and exhibits asymmetrical peak. Emission spectra can be fitted by Gaussian fitting to three peaks, it is because Eu2+ can occupy three positions of the matrix. In order to get a better green emission, a series of samples(Ba1-ySry)9Lu2Si6O24:Eu2+ were prepared, and the emission peak red moved from 505 nm to 521 nm successfully. 3. A series of single-phased emission-tunable SrCaAl2SiO7:Dy3+, Tm3+ phosphors were successfully synthesized by solid-state reaction process. By controlling the energy transfer, the emission colors could be tuned from blue to yellow, including the white light region. It was discovered that the energy is transferred from Tm3+ to Dy3+ by luminescence spectra and decay curves. The resonancetype energy transfer from Tm3+ to Dy3+ was demonstrated to be via the dipole–dipole mechanism. By changing the doping concentration of Dy3+ and Tm3+ in SrCaAl2SiO7, the sample with corresponding color coordinates close to the white color chromaticity coordinates(x = 0.33, y = 0.33) could be realized. |
PDF Full Text Request