Growth And Upconversion Luminescence Of Er³⁺/Yb³⁺ Doped C12A7Single Crystal

C12A7is a kind of alternative material of TCO (transparent conductive oxide).Its structure and optical properties would be changed when the inner ions werereplaced. Ions in the cage-like structure of C12A7could be substituted by other ionsthrough implantation, chemical reduction and other ways. Lattice constant wasdetermined by the diameter and state of inner ions. The substitute ions could be e-,H-, Cl-, OH-and F-. These oxygen were replaced and formed a new compound.C12A7sinlge crystal and doped C12A7powder crystal were prepared byCZ(Czochralski) method and solid-phase method respectively in this paper. Processfor growing C12A7single crystal was studied. The research showed that theatmosphere in the furnace, growth rate and temperature condition had greatinfluence on the single crystal, the oxygen content is one of the key factorsdetermining the crystal quality, excessive oxygen content will cause oxidation ofcrucible and introduce coloration and bubble defects, but less content of oxygen willcause the decomposition. When the oxygen content in the melt is higher, dissolvedoxygen will form bubble defects in crystallization process. At the same time, thecrucible material will be oxidized and introdue Ir4+ions. A small amount of bubbledefects could be eliminated by annealing. The optimum technology was thatatmosphere condition was0.5%O2containing N2atmosphere; the raw material wasCaCO3and a-Al2O3; crystal growth temperature was1350°C; lifting speed was1mm/h; the rotating speed was5-10rad/min; the surface temperature was30°C/h;the annealing temperature was1300°C; the temperature gradient was50°C/h.Efects on its optical and electrical properties of C12A7were studied bytheoretical analysis caused by iternal ions. Functional theory and generalizedgradient approximation were selected in quantum chemical methods. The cutoffenergy was340eV; the K point was4×4×4ensuring energy convergence(<10-6eV) calculated. The inner ions affected the properties of C12A7crystalanalysed by quantum chemistry when the polarization was increased with the ions,the Fermi level was increased. The Fermi level of C12A7materials and derivativeswere formed by the inner ions and the framework. A metal bond was formedbetween the frame structure and the free ions. Fermi level of C12A7and itsderivatives were changed when changing the inner ions. C12A7derivatives weregotten by oxidation and reduction respectiively. The ion exchange process wasanalysed through the structure and optical properties. The results showed that C12A7can be oxidized to C12A7:Oin an oxidizing atmosphere, C12A7can bereducted to C12A7:H-in an reducing atmosphere.The Er3+/Yb3+doped C12A7power crystal as prepared by solid reaction. Thecontent of Er3+was1mol%and the contents of Yb3+increased from0%mol to20mol%. Strong green and red emissions were found in the samples which wereincreased with the contents of Yb3+. But the increase of the red emission was greaterthan the green one. In order to analyze the luminescence mechanism of Er3+andYb3+ions, the intensity of red and green light as adjusted to the same ensuring thewhole process, Er ions and Yb ion corresponded the ratio of1:10. Emission of530nm and550nm correspond to the2H11/2/4S3/b2—4I15/2of Er3+. Emission of660nmcorrespond to the4F9/2—4I15/2of Er3+. Er3+/Yb3+C12A7single crystal as prepared byCzochralski method and the upconversion emission was tested. The upconversionluminescence characteristics found in Er3+/Yb3+1:10crystals caused by Effectfrom the segregation coefficient of the dopant ions, the ion concentration in thecrystal has an offset, obtained by adjusting the concentration ratio of1:1red greencrystal doping concentration.Band structure of Er3+-doped C12A7and pure C12A7crystals were comparedto study the effects of doped ions. The results showed that doped ions C12A7hadchanged the band structure but not the Fermi level. C12A7:e-were prepared bymetal reduction and hydrogen reduction. Small polaron conduction mechanism asfound by testing conductiveity. Theoretical analysis on C12A7compared with Erdoped C12A7showed that no rare earth ions entered into interior of the cage-likestructure, but a substitutional ion. The bandwidth of Er3+doped C12A7wasincreased and the optical absorption range was decreased compared with C12A7, sothe metal properties were increased in Er3+doped C12A7.