Red, green, and blue upconversion luminescence of trivalent-rare-earth ion-doped Y2O3 nanocrystals

Trivalent-rare-earth ion-doped ${\mathrm{Y}}_2{\mathrm{O}}_3$ nanocrystals have been synthesized, and their photoluminescence properties have been studied under 980 nm laser diode excitation. The crystallite size estimated by x-ray diffractometry and scanning electron microscopy was about 30–40 nm. In ${\mathrm{Yb}}^{\text{3+}}$ and ${\mathrm{Tm}}^{\text{3+}}$ codoped ${\mathrm{Y}}_2{\mathrm{O}}_3$ nanocrystals, the bright blue emissions near 450 and 480 nm have been noticeable due to the ${}^1{D}_2{–}^3{F}_4$ and ${}^1{G}_4{–}^3{H}_6$ transitions of ${\mathrm{Tm}}^{\text{3+}},$ respectively. The bright green emissions of ${\mathrm{Er}}^{\text{3+}}$ doped ${\mathrm{Y}}_2{\mathrm{O}}_3$ nanocrystals appeared near 530 and 550 nm were assigned to the ${}^2{H}_{\text{11/2}}{–}^4{I}_{\text{15/2}}$ and ${}^4{S}_{\text{3/2}}{–}^4{I}_{\text{15/2}}$ transitions of ${\mathrm{Er}}^{\text{3+}},$ respectively. The ratio of the intensity of green luminescence to that of red luminescence has decreased with an increase of concentration of ${\mathrm{Yb}}^{\text{3+}}$ in ${\mathrm{Er}}^{\text{3+}}$ doped ${\mathrm{Y}}_2{\mathrm{O}}_3$ nanocrystals. In sufficient quantities of ${\mathrm{Yb}}^{\text{3+}}$ to ${\mathrm{Er}}^{\text{3+}},$ the bright red emission near 660 nm has been predominant due to the ${}^4{F}_{\text{9/2}}{–}^4{I}_{\text{15/2}}$ transition of ${\mathrm{Er}}^{\text{3+}}.$ The primary color components are in these red, green, and blue emissions, from which a wide spectrum of colors, including white, would be produced by appropriate mixing them.