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Enhanced upconversion and downshifting emissions from Tm3+, Yb3+ co-doped CaZrO3 phosphor in the presence of alkali ions (Li+, Na+ and K+)
摘要： The Tm3+, Yb3+ co-doped CaZrO3 phosphor samples have been synthesized through solid state reaction method in the absence and presence of alkali metal ions (i.e. Li+, Na+, K+). The X-ray diffraction (XRD) study shows the formation of CaZrO3 crystal with orthorhombic phase. The Tm3+, Yb3+ co-doped CaZrO3 phosphor emits intense upconversion emission in blue (474 nm) and NIR (799 nm) regions due to 1G4 → 3H6 and 3H4 → 3H6 transitions of Tm3+ ions, respectively on excitation with 980 nm radiation. The emission intensity is significantly enhanced in the presence of alkali ions due to charge compensation and asymmetry in the crystal field. The emission intensity in the case of Na+ co-doped phosphor is maximum and at 1 W pump power, it is increased by ~ 44 and ~ 31 times in blue and NIR regions, respectively as compared to without alkali ions co-doped phosphor. The downshifting emission in blue region has been observed due to oxygen vacancy and Tm3+ ions on excitation with 277 and 360 nm radiations which is enhanced significantly in the presence of alkali ions. Thus, the intense blue emission by this material is suitable for blue and white light emitting phosphors.
关键词： Calcium Zirconate,Downshifting,Alkali ions,Upconversion,Rare earth
更新于2025-09-19 17:15:36
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Bandgap opening in graphene using alkali ions by first principles
摘要： Recently, bandgap opening at the Dirac point in graphene, formed on SiC(0001) surfaces, has been reported in different experiments, by deposition of positively charged alkali ions. This is clearly of great relevance for the countless practical applications of graphene in nano-electronic devices. By first principles calculations, based on the Density Functional Theory, the electronic band structure and the energetic properties are obtained for Na+, K+, and Cs+ ions interacting with graphene on SiC. We show that simple adsorption of alkali ions on intact graphene cannot give rise to a significant energy gap. An appreciable bandgap opening, similar to that observed in actual experiments, occurs instead due to the formation of Stone-Wales defects and substitutional defects (where positively charged alkali ions replace carbon atoms) that lead to a significant breaking of the charge symmetry among the carbon atoms of pristine graphene.
关键词： bandgap opening,graphene,alkali ions,Stone-Wales defects,substitutional defects,Density Functional Theory,first principles
更新于2025-09-09 09:28:46