Novel blue-emitting LaOBr:Eu(2+) and LaOI:Eu(2+) phosphors have been successfully synthesized and compared to LaOCl:Eu(2+). The emission spectra of LaOX:Eu(2+) (X = Cl, Br, and I) show that the peak maxima change somewhat to the red-shift region; 425 nm for LaOCl:Eu(2+), 427 nm for LaOBr:Eu(2+), and 431 nm for LaOI:Eu(2+), which is quite opposite to one based on spectrochemical series (I(-) < Br(-) < Cl(-)). From diffuse reflectance spectra, the band gap energies for LaOCl, LaOBr, and LaOI host lattice are estimated as 5.53 eV (44,594 cm(-1)), 5.35 eV (43,142 cm(-1)), and 4.82 eV (38,868 cm(-1)), respectively, using the Kubelka-Munk function. For LaOX host lattices, the band gap energies are gradually decreased going from Cl to I as the order of energy levels of np orbitals is Cl 3p < Br 4p < I 5p. A quantum wave function calculation from crystal field theory (CFT) indicates the same tendency with experimental data in the LaOX:Eu(2+) (X = Cl, Br, and I) phosphor materials. With considerations of the radial wave function shape, crystral structure differences and electronegativities among phosphor materials, the splitting energies of 5d orbitals are calculaed; ΔECl = 14,597 cm(-1), ΔEBr = 14,864 cm(-1), ΔEI = 15,001 cm(-1) for LaOX:Eu(2+) (X = Cl, Br, and I). It is noteworthy that the crystal field strength decreases when the interatomic distance decreases, which is probably dependent on the ionic radius of halide ions in the series of LaOX:Eu(2+) phosphor materials.
Current appropriate technology promoting social sustainability for rural, underprivileged populations is often plagued by lack of affordability, maintenance, and personal training, and is also empathetically disconnected from local people and culture. This study proposes criteria for balancing design thinking processes and appropriate technology for social sustainability. In this study, we concretized five assumptions for design thinking processes: user-oriented design with mass productivity; reiterative nature through user satisfaction surveys; affordability for purchase, maintenance, and repair services; local appropriateness; and eco-friendliness with environmental sustainability. Next, we applied the criteria to 28 representative cases from the water, energy, health, shelter, and transportation fields. The cases were evaluated using qualitative content analysis. Findings show that the criteria are necessary for setting economic, social, and environmental development goals for underprivileged regions after considering local contexts. Cultural empathy and collaboration with locals are key for finding practical solutions and co-creating options iteratively. Further, the cases were compared quantitatively using radar diagrams, histograms, and graphs showing average values and standard deviations, providing an objective measure for appropriate technology. Notably, both qualitative and quantitative approaches can serve as useful guidelines for designers, developers, and local users when developing appropriate technology for social sustainability in underprivileged regions.
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