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The effect of the phosphor curvature in the range 0.1766-0.2589 mm−1 on the luminous efficacy of Y2.95Al5O12:0.05Ce3+ ( YAG)-based white-light-emitting diodes ( WLEDs) was investigated at the similar correlated color temperature ( CCT) of ~6300 K by tuning the concentration of YAG phosphors in the phosphor layer ranging from 7.5 to 15 wt%. It was found that both the luminous efficacy and luminous power increased monotonically with the increasing curvature. The luminous efficacy (=82.4 lm/W) and luminous power (=297.85 mW) of the YAG-based WLED at the preferable phosphor curvature of 0.2589 mm−1 were 19.44% and 17.36%, respectively, higher than those at the curvature of 0.1766 mm−1 under 350 mA. This finding reveals that the surface curvature of phosphor layers is a critical factor which cannot be ignored for the investigation of the light output of phosphor-converted WLEDs. Moreover, the color rendering index ( CRI) enhancement of YAG-based WLED with substitution of Y2.94Al5O12:0.05Ce3+, 0.01Pr3+ (YPrAG), Y2.45Gd0.5Al5O12:0.05Ce3+ (YGdAG), and Y2.95Al4.8Si0.2O11.8N0.2:0.05Ce3+ (YAlSiON) for YAG were assessed under the same phosphor curvature of 0.2589 mm−1 and the similar CCT ~6350 K. Taking the luminous efficacy, preparation cost of phosphors, and CRI into consideration, we suggest that the YGd AG is a preferable candidate for replacing the YAG for use in WLEDs among the four kinds of phosphors. Compared with the YAG (7.5 wt%)-based WLED, the YGd AG (7 wt%)-based WLED exhibited an improved CRI, less preparation cost of phosphors, and the acceptable reduction in luminous efficacy under 350 mA. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, high-quality wurtzite indium nitride was epi-grown on sapphire substrates by plasma-assisted metal-organic molecule beam epitaxy system (PA-MOMBE). Structural and electrical properties of the InN films were significantly improved by employing a GaN buffer layer. In addition, high-resolution X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy (TEM), Hall Effect, Raman and photoluminescence spectroscopy were carried out to characterize the effect of the growth temperature on structural and optoelectronic properties. It was found that highly c-axis oriented InN epilayer can be obtained by optimizing growth conditions. TEM images reveal that the epitaxially grown InN/GaN interface is sharp, and the spacing of the InN(0002) lattice plane is about 0.57nm. Raman spectra also show a sharp peak at 491cm−1 attributed to the E2(high) mode of wurtzite InN. These results indicate that the improvement of InN material quality can be achieved using heteroepitaxy on GaN/sapphire templates. [Copyright &y& Elsevier]