Optimization of Gd[sub 2]O[sub 3]-Based Red Phosphors Using Combinatorial Chemistry Method

Abstract

Combinatorial chemistry was applied to the optimization of (Gd 2ϪxϪy M x )O 3 :Eu y 3ϩ phosphors for displays. The (Gd 2ϪxϪy M x )O 3 :Eu y 3ϩ phosphor is a promising candidate for red field emission display ͑FED͒ phosphors. Screening was performed in terms of cathodoluminescence at a low voltage excitation and photoluminescence. We developed a ternary material library of a triangle-type composition array to obtain the optimum composition of co-dopants. Three co-dopants ͑Al, Ca, Mg͒ were introduced into Gd 2 O 3 :Eu 3ϩ . Gd 2 O 3 was a good host material for red FED phosphors at a low voltage excitation, and the cathodoluminescent efficiency of Al co-doped phosphor, ͑Gd 1.83 Al 0.05 ͒O 3 :Eu 0.12 3ϩ , was superior to that of the commercial red phosphor Y 2 O 3 :Eu 3ϩ . We also investigated the energy transfer between Eu 3ϩ ions by analyzing the decay curves of emissions originating from 5 D 0 energy states in terms of multipolar interactions. We can explain the quenching of emissions from 5 D 0 in terms of a newly proposed cross relaxation in association with an intercenter diffusion.There has been a growing interest in Eu 3ϩ doped red phosphors for applications in field emission or electroluminescent displays. The Gd 2 O 3 :Eu 3ϩ phosphor is a promising candidate material for red field emission display ͑FED͒ phosphors. The solution combinatorial chemistry 1,2 was adopted for optimized phosphor materials discovery. Xiang et al. developed the combinatorial approach to discover efficient red, green, blue ͑RGB͒ phosphors based on solid-state combinatorial chemistry. 3,4 Combinatorial methods make it possible to rapidly synthesize, process, and analyze large libraries ͑with hundreds to thousands of members͒, dramatically accelerating the rate at which these experiments can be designed, executed, and analyzed.Conventional solid-state combinatorial chemistry, in which phosphors are dealt with based on thin-film technology, is carried out on a large scale. A huge number of compounds are given on the small substrate and synthesized at one time, but the amount of each compound is too small to be characterized properly, and thin-film properties may be different from powder properties. 5-7 To overcome these problems, solution-based combinatorial chemistry has been developed and applied to the synthesis of phosphor powders. Thus, we adopt solution combinatorial chemistry in search of optimized phosphor materials. We have developed a scanning multi-injection delivery system to deliver microliter volumes of precursor solutions to sample sites rapidly and accurately. The combinatorial chemistry method adopted here makes it possible to characterize all the properties of an individual compound in the libraries in the same way as for a conventional individual powder sample. Thus, we can use conventional UV and cathodoluminescence ͑CL͒ spectroscopic techniques to measure all properties of a member compound in the libraries of materials.In our present combinatorial approach, we investigate the effect of some co-dopants on the CL eff...

Luminescent mechanism of Eu3+-doped epitaxial Gd2O3 films grown on a Si (111) substrate using an effusion cell

“…Hence, the optimal concentration of Eu 3þ for maximum intensity was determined to be 0.18 mol. This value is much less than previously reported results for chemically synthesized Gd 2 O 3 :Eu 3þ [15]. However, if there are differences in surface morphology among Gd 2 O 3 :Eu 3þ films, this luminescence intensity has to be corrected because the luminescence efficiency is increased when the surface is rough.…”

“…4 shows the 1/e decay times for different Eu 3þ concentrations. From this figure, we estimated the critical concentration for radiative transition to be approximately 0.11 mol, indicating that physically evaporated Gd 2 O 3 :Eu 3þ film has a smaller critical concentration than that of chemically synthesized film, which is 0.4 mol [15]. Using the above formula, we calculated the critical distance to be 11.1 Å which is about 4 Å larger than that of chemically synthesized Gd 2 O 3 :Eu 3þ [15].…”

“…From this figure, we estimated the critical concentration for radiative transition to be approximately 0.11 mol, indicating that physically evaporated Gd 2 O 3 :Eu 3þ film has a smaller critical concentration than that of chemically synthesized film, which is 0.4 mol [15]. Using the above formula, we calculated the critical distance to be 11.1 Å which is about 4 Å larger than that of chemically synthesized Gd 2 O 3 :Eu 3þ [15]. This result means that the PL from the evaporated thin film decays faster than the PL of chemically synthesized Gd 2 O 3 :Eu 3þ because of a greater probability of cross-relaxation between Eu 3þ ions and a smaller probability of non-radiative transition, even when films have the same Eu 3þ concentration.…”

“…The results of theoretical calculations show that this type of transition has R ÀS dependence, where R is the distance between the sensitizer (Gd 2 O 3 ) and activator (Eu 3þ ) and S equals 6 for the electric dipoleedipole interaction. However, reported experimental data for Gd 2 O 3 :Eu 3þ phosphors show that the observed S values are not consistent with the theoretical value of 6 [15]. To prove the luminescent mechanism of Gd 2 O 3 :Eu 3þ materials with no interference from crystalline defects, growth of epitaxial films with perfect crystallinity is essential.…”

Influence of morphological transformation on luminescence properties of europium-doped gadolinium oxide nanostructures

“…fluorescence labels [9][10][11][12]. Since the morphology and dimensionality of nanostructures are vital factors, which particularly have an effect on the physical, chemical, optical, and electronic properties of materials, it is expected that rare-earth-doped oxides synthesized in nanoscale form of may take on novel spectroscopic properties of both dimension-controlled and modified ion-phonon confinement effects compared to their bulky counterparts.…”