Luminescence properties of M2MgSi2O7:Eu2+ (M = Ca, Sr) phosphors and their effects on yellow and blue LEDs for solid-state lighting

The akermanite phosphors of Eu2+ activated M2MgSi2O7 (M = Ca, Sr) were synthesized by solid-state reactions under a weak reductive atmosphere, and systematically characterized by photoluminescence excitation and emission spectra, lifetime, concentration quenching, diffuse reflection spectra and thermal quenching process in the temperature range of 100-400 K. In Ca2MgSi2O7:Eu2+ there are at least two distinguishable sites, resulting in one broad emission situating at about 450 nm and another dominating around 535 nm, and in Sr2MgSi2O7:Eu2+ only a blue emission around 468 nm is observed. Both phosphors can be efficiently excited in the wavelength range of 250-425 nm where the near UV (similar to 395 nm) Ga(In)N LED is well matched. The lifetimes of Eu2+ ions in these samples are around microsecond. The concentration of Eu2+ ions in Ca analog is optimized at about 1.5 mol%. By combining M2MgSi2O7:Eu2+ (M = Ca, Sr) phosphors with near UV Ga(In)N chips, intense yellowish-green (Ca) and blue LEDs (Sr) are obtained, respectively. The blue LED shows better stability on chromaticity and better saturation on luminous intensity as the direct current increases. Such difference is considered to be due to the different thermal effect on the peak position, luminescent intensity and full-width half-maximum (FWHM) of Eu2+ ions in M2MgSi2O7 (M = Ca, Sr). These results show that M2MgSi2O7:Eu2+ (M = Ca, Sr) phosphors exhibit potential applications in the field of white LEDs. (c) 2007 Elsevier B.V. All rights reserved.