Sensitized thulium blue upconversion emission in Nd3+/Tm3+/Yb3+ triply doped lead and cadmium germanate glass excited around 800 nm

Abstract

Bright blue upconversion emission by thulium ions in PbGeO3–PbF2–CdF2 glass triply doped with Nd3+–Tm3+–Yb3+ under diode laser excitation around 800 nm is reported. The results revealed that the Nd3+/Tm3+/Yb3+-codoped sample generated ten times more 475 nm blue upconversion fluorescence than the Yb3+-sensitized Tm3+-doped one, under the same excitation power. The upconversion process also showed a strong dependence upon the Yb3+ concentration. The results also indicated that the neodymium ions played a major role in the upconversion process by transfering the 800 nm excitation to thulium ions. The population of the Tm3+ ions G41 emitting level was accomplished through a multiion interaction involving ground-state absorption of pump photons around 800 nm by the Nd3+(4I9/2→2H9/2, 4F5/2) and Tm3+(3H6→3F4) ions followed by energy-transfer processes involving the Nd3+–Yb3+(4F3/2, 2F7/2→4I11/2, 2F5/2) and Yb3+–Tm3+(2F5/2, 3F4→2F7/2, 1G4) pairs.