Li~+共掺杂对掺Er~(3+):TiO_2上转换发光的增强作用·

采用非水性溶胶-凝胶法制备了0.1%Er~(3+)(摩尔分数,下同)、0%～2%Li~+共掺杂TiO_2粉末,在980nm半导体激光器(LD)激发下获得了中心波长526nm、550nm的绿色和663nm的红色上转换发光.Li~+共掺杂对掺Er~(3+):TiO_2的相结构未产生影响,但极大增强了上转换发光强度.随Li~+共掺杂摩尔分数的逐渐增大,绿色和红色上转换发光强度先增大后减小,当Li~+摩尔分数为1%时,上转换发光强度达到最大,绿色和红色上转换发光强度分别比掺Er~(3+):TiO_2提高了约330倍、30倍和60倍.Er~(3+)Li~+共掺杂TiO_2粉末的绿色和红色上转换发光均为双光子吸收过程.Li~+共掺杂不改变Er~(3+)的上转换发光机制,但破坏了Er~(3+)的局部晶体场对称性,影响了Er~(3+)内部4f能级的跃迁几率,导致上转换发光强度增强.

Enhanced Upconversion Emissions of Er~(3+)-doped TiO_2 by Li~+Codoping

The 0.1%Er~(3+)-doped TiO_2 powders with 0%～2%Li~+codoping are performed by the non-aqueous sol-gel method.The green and red upconversion emissions centered at about 526nm,550nm and 663nm are detected by a 980nm semiconductor laser diode excitation.The codoping of Li~+has no effect on the structure of Er~(3+):TiO_2,however,strongly improves the upconversion emission intensity.With increasing the codoping concentration of Li~+,the intersity of green and red upconversion emissions increases at first and then decreases,with highest intensity for 1%Li~+ codoping.The intensity of green and red emission is about 330 times,30 times and 60 times greater than that of Er~(3+)-doped TiO_2 without Li~+.The two-photon absorption upconversion process is involved in the green and red upconversion emission of Er~(3+)-Li~+codoped TiO_2.The codoping of Li~+does not change the upconversion mechanism of Er~(3+),but distort the local field symmetry of the Er~(3+) and hence increases the intra-4f transitions of Er~(3+),which enhances the upeonversion emission intensity of Er~(3+):TiO_2.