Low-Concentration Eu²⁺-Doped SrAlSi₄N₇: Ce³⁺ Yellow Phosphor for wLEDs with Improved Color-Rendering Index

Luminescence property of low-concentration Eu²⁺-doped SrAlSi₄N₇:Ce³⁺ yellow phosphor is reported in this paper. Three optical centers Ce1, Ce2, and Eu2 are observed in the phosphor. Deconvolution of emission spectrum confirms the three centers to be green (530 nm), yellow (580 nm), and red (630 nm), respectively. This property promises considerable improvement of color-rendering property of a white light-emitting diode (wLED). For example, color-rendering index (CRI) of wLED fabricated by combining a blue LED chip and SrAlSi₄N₇:0.05Ce³⁺,0.01Eu²⁺ phosphor reaches 88. A competitive energy transfer process between Ce1-Ce2 and Ce1-Eu2 is confirmed based on Inokuti-Hirayama formula. Ratio of energy transfer rate between Ce1-Ce2 and Ce1-Eu2 (W_Ce1-Eu2/W_Ce1-Ce2) is calculated to be 2.0. This result reveals the effect of Eu²⁺ concentration on quantity of green and red components in SrAlSi₄N₇:Ce³⁺,Eu²⁺ phosphor.