Photoluminescence, Non-Reduction and Thermal Stability Characteristics of Red Phosphors Ca_3La_(3(1-X))Eu_(3X)(BO_3)_5 Prepared in Reducing Atmosphere

摘要

A series of Ca_3La_(3(1-X))Eu_(3X)(BO_3)_5 phosphors were prepared via a solid-state reaction under reducing atmosphere. Rietveld refinements were performed by adopting the powder X-ray diffraction data, which indicates the occupations of Eu~(3+) on both La~(3+) and Ca~(2+) sites with a preferred location on the La~(3+) site over the Ca~(2+) site. This kind of phosphors could be excited by UV and blue LED in solid-state lighting technology and the CIE chromaticity coordinates for phosphors CLBO: 0.06Eu~(3+) (λ_(ex) = 254 nm) and CLBO: 0.12Eu~(3+) (λ_(ex) = 393 nm) are (0.6712, 0.3328) and (0.6685, 0.3287), respectively, which are compliant with the national television system committee (NTSC) standard for red chromaticity. The energy transfer rate between the Eu~(3+)-Eu~(3+) pairs is weak that proved by the results of the decay process and the efficiency of the Eu~(3+) ~5Do->-~~7F_2 emission. The mechanism responsible for the non-reduction of Eu~(3+) was analyzed, which was determined by two factors: 1) no element of the host matrix can be oxidized and 2), cationic vacancies which can be regarded as the electron donor cannot exist. The temperature dependence study shows thermal quenching behavior is attributed to crossover from the ~5Do excited state of the Eu~(3+) to the charge transfer state band and these phosphors have good thermal stability.