Synthesis And Luminescence Properties Of A Single-Phased Na_0.34Ca_0.66Al_1.66Si_2.34O₈Phosphor For UV-Pumped White LEDS

Nowadays, Light-emitting diodes (LEDs) have attracted much interest due to their superior features, such as energy saving, longer lifetime and environmental friendliness, and will be a new solid-state lighting to replace the incandescent lamp and fluorescent lamp in the21st century. The most common method to generate white light-emitting diodes is a combination of a chip with a phosphor. A single-phased full-color emitting phosphor upon UV-LED chip is considered to be potentially useful due to stability, small color aberration, high color-rendering index and low correlated color temperature. In recent years, because of the excellent luminescence properties such as stable crystal structure, high chemical stability and high optical conversion efficiency, aluminosillcate-based phosphors have drawn much attention.Ce3+-doped, Ce3+-Tb3+co-doped and Ce3+-Sm3+co-doped Na0.34Ca0.66Al1.66Si2.34O8(NCASO) phosphors have been synthesized via a high temperature solid-state reaction method. The crystal characteristics, luminescence properties as well as the energy transfer mechanism from different ions of the phosphors are investigated. The main results obtained are listed as follow:(1) Na0.34Ca0.66Al1.66Si2.34O8:Ce3+phosphors were synthesized by the high temperature solid-state reaction method. All of the profiles match well with the Joint Committee for Powder Diffraction Standard file86-1650for NCASO. No additional XRD peaks are found, indicating that pure phase of NCASO can be obtained at1300℃for2h. It can be seen that the PLE spectra monitored at414nm show a broad absorption band ranged from240to380nm. It corresponds to the4f-5d transition of Ce3+ions. Under335nm excitation, the emission spectra shows a broad blue-green emission band extending from375nm to550nm with a maximum at about414nm which corresponds to the5d-4f transition of Ce3+It is observed that the PL intensity is affected by Ce3+concentration. With the increase of Ce3+ions concentration, the emission intensity increases and reaches a maximum at0.0075.(2) Na0.34Ca0.66Al1.66Si2.34O8:Ce3+, Tb3+phosphors were synthesized by the high temperature solid-state reaction method. Under340nm excitation, the emission spectra showed a broad emission at about414nm which corresponds to the5d-4f transition of Ce3+and several emission with a maximum at about544nm of Tb3+corresponding to the5D4-7F5transition. With the Tb3+ions concentrations increases, the emission intensity of Tb3+ions at544nm increases and reaches a maximum at0.01. The emission intensity of Ce3+at414nm was simultaneously found to decrease. It indicates that the energy transfer mechanism between Ce3+and Tb3+ions is dipole-dipole interaction in NCASO:Ce3+, Tb3+phosphor.(3) Na0.34Ca0.66Al1.66Si2.34O8:Ce3+, Sm3+phosphors were synthesized by the high temperature solid-state reaction method. Under340nm excitation, NCASO:Ce3+, Sm3+phosphor showed a broad emission band at414nm of Ce3+and four emission bands from550nm to725nm of Sm3+with a maximum at about600nm corresponding to the4G5/2-6H7/2transition. Moreover, the emitting colors can be adjusting from blue to white by proper tuning of the relative composition of Ce3+/Sm3+. The analysis based on Inokuti-Hirayama model indicates that the ET is governed by electric dipole-dipole interaction.The strong absorption of the Na0.34Ca0.66Al1.66Si2.34O8:Ce3+, Tb3+, Na0.34Ca0.66Al1.66Si2.34O8:Ce3+, Sm3+phosphors in the range of250-380nm suggests that they have great potential for WLED.