Tuning the color purity of LaAlO3:Eu3+ red phosphor by the cross relaxation

Abstract

Precisely adjusting the color purity of LaAlO 3 :Eu 3+ red phosphor with 593 and 618 nm emissions is achieved in a strategy of suppressing transitions of high energy levels of Eu 3+ ions through varying the doping concentration. As the doping concentration increases, the transitions from high levels 5 D 3,2,1 will be weakened, while those from 5 D 0 are enhanced up to a critical value with the aid of the cross relaxation. As a result, an increase of the color purity from 95.2% to 97.4% is obtained. It indicates that the red phosphor could be one of the excellent red-light-emitting phosphors in illuminating and display devices.For the applications of energy-saving fluorescent lamps, solid state lighting and high resolution display devices, phosphor materials [1][2][3] , especially red-light-emitting phosphors with a high color rendering index (CRI), high efficiency and high color purity are in the urgent need. Lots of candidate phosphors with those merits, including Eu 3+ -doped Na 5 La (MoO 4 ) 4 [4] , Gd 2 (MoO 4 ) 3 [5] , Y 2 O 3 [6] , CaO [7] , Gd 1-x Zn x O 3 [8] , Eu 2+ -doped Ca 1-x Sr x S [9] , Sr 2 Si 5 N 8 [10] , CaAlSiN 3 [11], Mn-doped BaZnOS [12] , CaAl 12 O 19[13] and Ce 3+ -doped CaSiN 2 [14] red phosphors, have emerged recently. Generally, due to the narrow line emission of Eu 3+ other than the broad band emission, Eu 3+ -doped red-light-emitting phosphors show better color purity than those with Eu 2+ and Ce 3+ . Specifically, there are two types of transitions for Eu 3+ : one is the electric dipole 5 D 0 -7 F 2 transition ranging from 610 to 625 nm as Eu 3+ occupies some sites of cations in a non-centrosymmetric lattice, and the other is the magnetic dipole 5 D 0 -7 F 1 transition, ranging from 590 to 600 nm as Eu 3+ substitutes some sites of cations in a centrosymmetric lattice [15] . Consequently, a dependence of the red-light-emission position on the CRI and lumen output could be established [16] . Namely, the emissions peaked in 610-625 nm exhibit higher CRI, while those peaked in 590-600 nm give greater lumen output than in other wavelength ranges.Thus, a compromise strategy is expected to explore a redlight-emitting phosphor with emissions covering both two ranges concurrently. In our previous results [17] , a perovskite type LaAlO 3 :Eu 3+ red phosphor is obtained with peaks at 593 nm and 618 nm, much similar to those reported by Ekambaram [16] and Hreniak [18] . However, some transition emissions from high levels ( 5 D 1,2,3 ) to 7 F J are still found in the blue-green region. These transitions are generally undesirable as they most likely degrade the color purity. Some efforts, therefore, have to be made to achieve higher color purity through suppressing transitions of Eu 3+ from high levels 5 D 1,2,3 to 7 F J , ensuring an efficient transition from 5 D 0 to 7 F 1 and 7 F 2 simultaneously.In this paper, we report an efficient adjustment for the color purity with the aid of the cross relaxation by simply varying the doping concentration of Eu 3+ ions.A conventional solid-state reaction me...

Synthesis and down conversion emission property of $$\hbox {Eu}^{3+}$$ Eu 3 + doped $$\hbox {LaAlO}_{3}, \hbox {CsAlO}_{2}$$ LaAlO 3 , CsAlO 2 and $$\hbox {LiLaO}_{2}$$ LiLaO 2 phosphors

“…Other weak intensity peaks are seen on either side of strong peaks. The two weak emission peaks at 536 and 557 nm are due to 5 D 2 → 7 F 3 and 5 D 1 → 7 F 2 transitions as reported in reference (Mao et al 2010). The intensity ratio of 591 nm peak to 616 nm peak is a measure of asymmetry of the Eu 3+ site in the host lattice (Blasse and Grambier 1994).…”