Development of a Blue Emitting Calcium-Aluminate Phosphor

Abstract

We report methodological advances that enhance the phosphorescence efficiency of a blue-emitting calcium aluminate phosphor (CaAl2O4: Eu2+, Nd3+). The investigation of long-persistence blue-emitting phosphors is highly desirable due to their promising applications, such as white LEDs; however, the development of highly efficient blue-emitting phosphors is still challenging. Here, we have quantitatively characterized the phosphorescence properties of the blue-emitting phosphor CaAl2O4:Eu2+, Nd3+ with various compositions and directly related these properties to the quality of its luminescence. We optimized the composition of the activator Eu2+ and the co-activator Nd3+, the doping conditions with alkaline earth metals, alkali metals, and Si to create crystallographic distortions and, finally, the flux conditions to find the best parameters for bright and persistent blue-emitting phosphors. Our research has identified several doping compositions with good to excellent performance, with which we have demonstrated bright and persistent phosphors with afterglow characteristics superior to those of conventional phosphors.

d–f luminescence of Ce3+ and Eu2+ ions in BaAl2O4, SrAl2O4 and CaAl2O4 phosphors

“…It shows blue luminescence having peak at 440 nm. This is exactly the same as that reported by Palilla et al [11] and close to the result of Kim et al [37]. Observation of single emission band in CaAl 2 O 4 and SrAl 2 O 4 indicates emission from one site only.…”

Recent Developments in Lanthanide-Doped Alkaline Earth Aluminate Phosphors with Enhanced and Long-Persistent Luminescence

“…Various alkali metals have been employed as dopants to increase the afterglow intensity and lifetime. Dhananjaya 3+ phosphor with alkali metals (Li + , Na + , K + ) and alkaline earth metals (Mg 2+ , Ca 2+ , Ba 2+ ) can significantly boost the phosphorescence intensity and increase the afterglow lifetime [12,81]. These apparently imply that Si 4+ doping is also effective for enhancing the phosphorescence intensity.…”

“…Dhananjaya et al observed that the photoluminescence intensity of the Gd 2 O 3 :Eu 3+ phosphor remarkably increased after the incorporation of Li+, Na+, and K+ into this phosphor [ 105 ]. Kim et al also reported that the doping of SrAl 2 O 4 :Eu 2+ ,Dy 3+ , and CaAl 2 O 4 :Eu 2+ ,Nd 3+ phosphor with alkali metals (Li + , Na + , K + ) and alkaline earth metals (Mg 2+ , Ca 2+ , Ba 2+ ) can significantly boost the phosphorescence intensity and increase the afterglow lifetime [ 12 , 81 ]. These apparently imply that Si 4+ doping is also effective for enhancing the phosphorescence intensity.…”

“…This long-persistent luminescence was presumed to result from the trapping–transporting–detrapping of the holes, a process in which Nd 3+ ions behaved as hole traps between the ground and the excited states of the Eu 2+ ion. Kim et al reported the optimized composition of the Eu 2+ activator and Nd 3+ coactivator for CaAl 2 O 4 [ 81 ]. The introduction of Nd 3+ into the CaAl 2 O 4 :Eu 2+ system was found to significantly boost its phosphorescence intensity and lifetime, similar to that of Dy 3+ doping in the SrAl 2 O 4 :Eu 2+ system.…”

“…For example, the effect of the concentration of H 3 BO 3 as a fluxing agent on the structure, morphology, and luminescent properties of Ca 1−x Al 2 O 4 :xEu 2+ have been explored by Zeng et al [ 78 ] A comparison of different amounts of H 3 BO 3 for phosphor synthesis revealed that an H 3 BO 3 mass ratio of 0.5 wt.% resulted in a product with an adequate morphology without agglomeration and the best luminous intensity among the various samples. Kim et al also presented a comparative study of varying amounts of H 3 BO 3 [ 81 ], which suggested that 0.25 mol per mol of CaAl 2 O 4 :Eu 2+ ,Nd 3+ resulted in the brightest phosphorescence among the various samples; however, a higher concentration of H 3 BO 3 was found to produce a hardened final product, which can create difficulties in the subsequent mortar grounding process.…”