A yellow-emitting Ce3+ phosphor, La1−xCexSr2AlO5, for white light-emitting diodes

Abstract

A yellow-emitting phosphor, La1−xCex3+Sr2AlO5, is reported that displays a peak in the excitation at 450nm and a peak in the emission at 556nm. When this phosphor is pumped by a blue InGaN light-emitting diode (λmax=450nm) we obtain white light with color rendering index (Ra) between 81 and 85 and color temperatures between 4200 and 5500K, suggesting that this material is competitive as a blue-pumped yellow phosphors.

Photoluminescence properties and local electronic structures of rare earth-activated Sr3AlO4F

“…Since the strong excitation band of Ce 3+ extends to unusually long wavelengths covering from 350 to 480 nm with a maximum at about 405 nm, Sr 3 AlO 4 F:Ce 3+ ,Na + shows high promise for application in white-light UV-LEDs. As mentioned above, apart from few materials based on the garnet-like structure [6][7][8][9][10][11][12] and a LaSr 2 AlO 5 [13,14] related to the structure of Sr 3 AlO 4 F, Ce 3+ -activated oxide-based materials can hardly be excited efficiently by near-UV or blue light because the 5d excitation band of Ce 3+ normally is at higher energies ranging from UV to 360 nm [27]. A relatively large crystal field splitting in Sr 3 AlO 4 F:Ce 3+ ,Na + of ∼7600 cm −1 (estimated from the energy difference between the longest and the shortest excitation bands in the excitation spectrum) of the 5d levels of Ce 3+ could be mainly responsible for such long-wavelength absorption and excitation of the 5d levels of the Ce 3+ ions, since a contribution from the nephelauxetic effect should be very limited due to predominated ionic bond of Ce Sr -O and in particular Ce Sr -F having higher electronegativity difference ( ∼ 2.86 vs. ∼ 2.32 for Ce-F and Ce-O, respectively) in Sr 3 AlO 4 F. On the basis of the fact that the position of the 5d levels of Ce 3+ is generally located at relatively higher energy in a less covalent lattice, it is believed that the crystal structure of Sr 3 AlO 4 F, in particular the local crystal structure around the Sr ions, could be mainly responsible for the long-wavelength absorption and excitation bands of Sr 3 AlO 4 F:Ce 3+ similar to the case of YAG:Ce 3+ [8].…”

“…Similarly, several structurally related materials of Ce 3+ -doped Y 3 Ga 5 O 12 [8], Lu 3 Al 5 O 12 [9], Gd 3 Sc 2 Al 3 O 12 [10] and Ca 3 Sc 2 Si 3 O 12 [11,12] based phosphors with the garnet structure can also be efficiently excited by blue light and show broad emission in the spectral range of 480-560 nm with varying compositions. Apart from the garnet-like phosphors, within the oxide framework, recently Ce 3+ -doped LaSr 2 AlO 5 [13,14] was also found to be a yellow emitting phosphor with the emission maxima between 552 and 577 nm when excited by blue light in the range of 435-453 nm. In addition, Eu 2+ -doped alkaline earth silicates (e.g., M 2 SiO 4 :Eu 2+ , M = Ca, Sr, Ba) [15,16] were also proposed to be promising green and yellow emitting phosphors for use in blue-and UV-LEDs, respectively.…”

Effect of Eu 3+ concentration on the photocatalytic activity of LaSr 2 AlO 5 powders

“…This small difference in radius will introduce lattice distortions as the Eu concentration increases provoking a larger number of lattice defects. Moreover, Europium forms an octahedral configuration with oxygen (EuO 8 polyhedron) [36,37]. The effective charge of the EuO 8 polyhedron is negative and this is advantageous to attract the positive charges of MB (R-S + ) at the surface of the grains, favoring the adsorption of the molecules as observed in other systems such as TiO 2 which had a negative charge Ti-O − on its surface.…”

Orange emission enhancement by energy transfer in Sr3Al2O5Cl2:Ce3+, Eu2+ phosphor for solid-state lighting

“…Recently, the research on phosphors suitable for fabricating white-light-emitting diodes (LEDs) has attracted more attention [1][2][3][4]. Phosphor-converted LEDs is an important kind of solidstate lighting.…”