Preparation And Luminescent Properties Of Rare Earthions Doped M₂ZnSiO₄（M=Na,K）Based Red Luminescent Materials

The rare earth ion of Eu3+or Sm3+doped M2ZnSiO4(M=Na, K) red luminescent materials were synthesized by a sol-gel method. The crystal structure, morphology and luminescent properties of samples were characterized by infrared spectroscopy, X-ray diffraction, scanning electronic microscopy and fluorescence spectrum. Influences of flux H3BO3 amount and active ion(Eu3+ Sm3+) doped amount on the fluorescence properties of the samples were studied. The concentration quenching mechanisms of activators were investigated.The Na2ZnSiO4:Eu3+ red emitting phosphors were prepared by sol-gel method. The sample obtained belongs to monoclinic crystal system and the morphology is similar to ellipsoid. The excitation spectra of the samples primarily consisted of a group of sharp peaks and the wavelength range from 350 nm to 550 nm. The main excitation peak was located at 465 nm, belonging to 7F0→5D2 typical absorbing transition. The samples transmitted a strong red light under blue light excitation with a wavelength of 465 nm. The emission bands were located at 701,653,613,591 and 578 nm, corresponding to 5 D0→7FJ(J=4,3,2,1,0) transition of Eu3+, respectively. The strongest emission peak was located at 613nm which corresponds to 5 D0→7F2 emitting transition of Eu3+. The luminescent intensity increased at first and then decreased with the increase of Eu3+mole amount. When the dosage of Eu3+ was 5% in mole, the fluorescence powder emits the most intensive luminescent intensity. Adding flux H3BO3 to sample can improve the luminescent intensity effectively and the optimal dosage of H3BO3 was 0.8% in mole.Orange-red emitting phosphors Na2ZnSiO4:Sm3+ were synthesized by sol-gel method using H3BO3 as a flux. The Na2ZnSiO4:Sm3+ phosphor obtained belongs to monoclinic crystal system and the particle size is about 2μm. The excitation spectra of the fluorescence powders consisted of a series of linear excitation peaks and the wavelength range from 330 nm to 550 nm. The emission spectra were composed of there major emission peaks using near ultraviolet with a wavelength of 404 nm as excitation light source. The emission peaks were located at 650 nm,604 nm and 566 nm, corresponding to 4G5/2→6H9/2,4G5/2→6H7/2 and 4G5/2→6H5/2 typical transition of Sm3+. The main emission peak was located at 604 nm(4G5/2→6H7/2) as reddish-orange emission. The luminescent intensity increased at first and then decreased with the increase of Sm3+ mole amount and the optimal dosage of Sm3+was 3% in mole. The concentration quenching mechanism was electric dipole-electric dipole interaction according to the Dexter theory. When H3BO3 amount is 1.5% in mole, the luminescent intensity of Na2ZnSiO4:Sm3+ phosphor reaches to the maximum, and then decreases.The K.2ZnSiO4:Eu3+ red emitting phosphors were obtained by sol-gel method using Eu3+ as an activator, the fluorescence powders synthesized belongs to orthorhombic crystal system. The sample particles are similar to regular polyhedron. The excitation spectra were composed of five excitation peaks, corresponding to f→f typical transition of Eu3+. The strongest and relatively strong excitation bands were located at 465 nm(7F0→5D2) and 393 nm(7F0→5L6), respectively. The phosphors could display red emission under a blue light or near ultraviolet source excitation. The main emission peak with a centered wavelength of 617 nm. There does not appear the concentration quenching phenomenon in the concentration ranges of the experimental measurement. Based on the X-ray diffraction patterns of the samples doped different amount of Eu3+, the impurities phase of ZnSiO3 and Zn2SiO4 can be produced when the concentration of Eu3+ is higher than the dosage of 6%. The diffraction peaks intensity of impurities phase increase with continue increasing the Eu3+ content, while the diffraction peaks intensity of the principal crystalline phase KiZnSiO4 decrease gradually, so ensuring the optimal dosage of Eu3+ was 6%.The K2ZnSiO4:Sm3+ reddish-red emitting phosphors, which can be suitable for white light-emitting diode, were prepared by sol-gel method. Based on the X-ray diffraction data, the principal crystalline phase of the fluorescence powders doped a little amount of Sm3+is K2ZnSiO4, belonging to orthorhombic crystal system. The space group of the sample is Pca21(29). The emission spectra consisted of four remarkable emission peaks under a near ultraviolet source excitation with a wavelength of 403 nm. The most intense peak was located at 605 nm, which is attributed to 4G5/2→6H7/2 transition of Sm3+. The luminescent intensity firstly increased and then decreased with increasing of the Sm3+mole amount and the optimal concentration of Sm3+was 7%. The CIE coordinates of sample locate in the reddish-orange region and do not change as increasing the mass fraction of Sm3+. The luminescent intensity of sample tend to increase in a certain concentration ranges with increasing the proportion of H3BO3. When H3BO3 amount is 4%, the phosphor exhibits the strongest luminescent intensity.