Synthesis And Optical Properties Of Er³⁺,Na⁺Ions Codoped12CaO·7Al₂O₃Powders

A new up-conversion emission12CaO·7Al3O2(C12A7：Er³⁺，Na⁺) was prepared bychemical precipitation method followed by annealing inorganic precursors，The X-raydiffraction （XRD）, excitation spectra, emission spectra, were conducted to characterize themicrostructure of C12A7: Er³⁺,Na⁺powders and study their optical properties.The results of XRD indicated that the cage structural polycrystalline C12A7powders ofsingle cubic phase were obtained. The photoluminescence of C12A7: Er³⁺,Na⁺at roomtemperature were observed in the visible region by using980nm Ar+line as excitation source.410nm，480nm，550nm，660nm emission band were observed which attributed to²H_9/2â†'⁴I_15/2，²H_9/2â†'⁴I_15/2,²H_9/2â†'⁴I_15/2,⁴F_7/2â†'⁴I_15/2,4S3/2â†'⁴I_15/2,⁴F_9/2â†'⁴I_15/2of Er³⁺ions. Thepump power dependence of C12A7：Er³⁺，Na⁺on UC luminescence suggest two-photonprocess were occurred for green and red emission bands. For a fixed Er³⁺concentration，theluminescence properties as a function of Na⁺concentration were systematically studied under980nm excitation. Enhanced green emission at550nm was observed and the intensity was14times stronger than that of sample without Na⁺ion. Except for the charge compensation，thisenhancement was related to the structure distortion and decreasing centrosymmetry.Usually，the difference of valence state between rare-earth ions and cation could formanion or cation vacancies or free oxygen species （O2-or O-）in the cage of C12A7due tocharge compensation. Alkali metal Na⁺replace Ca2+will form anion vacancies or cationicclearance. Charge compensation is provided by the coupled substitution mechanisim, that is,the simultaneous substitution of two Ca2+by one Er³⁺and one Na⁺ion. The forbiddentransitions of intra-4f shell electrons in free Er³⁺ions have been allowed due to lack of theinversion symmetry in the Er³⁺position in C12A7crystal field. Doped Na⁺ions will enhancesthe visible green and red up-conversion emissions.Our results suggested that C12A7was an appropriate candidate for Er³⁺doping, Thestructural adjustment of Na⁺，which is expect to lead a broader range of applications, such asnanoceramics for volumetric displays, temperature sensors, UC lasers, biomedical imaging,DNA detection and photodynamic therapy.