New full-color-emitting phosphor, Eu2+-doped Na2−xAl2−xSixO4 (0 ≤ x ≤ 1), obtained using phase transitions for solid-state white lighting

Abstract

A new color-tunable Eu²⁺-doped sodium aluminium silicate, Na_2−x−yAl_2−xSi_xO₄:yEu²⁺ (0 ≤ x ≤ 1), phosphor system was investigated as a novel candidate for phosphor-converted white light-emitting diode (LED) applications and successfully synthesized by wet chemical methods based on the hydrolysis of tetraethyl orthosilicate (TEOS). Different crystal structures and emission spectra were obtained by varying the ratio of Al to Si in the phosphor Na_2−xAl_2−xSi_xO₄ with x value ranging from 0.25 to 0.55. The Na_2−x−yAl_2−xSi_xO₄:yEu²⁺ phosphor system emitted a maximum intensity at 470–600 nm when using a 395 nm excitation wavelength, and the emission was strongly affected by the crystal structures determined by the x value. Substitution of Eu²⁺ affected the center wavelength and emission intensity due to changes in the crystal-field effect, which was strongly dependent on the crystal structure. The LED device exhibited an excellent color-rendering index R_a of 93 at a correlated color temperature of 4258 K with CIE color coordinates of (0.3629, 0.3427) under a 20 mA forward-bias current. Based on these results, we are currently evaluating the potential application of Na_2−x−yAl_2−xSi_xO₄:yEu²⁺ as a white-emitting UV-convertible phosphor.