Effect of Yb3+ concentration on upconversion luminescence in Yb3+, Tm3+ co-doped Lu2O3 nanophosphors

Energy level diagram of the Tm3+ and Yb3+ ions with relevant excitation and emission processes scheme is shown in the above figure. The full arrows pointing upward/downward represent energy absorption/emission. The dotted arrows pointing downward represent multiphonon relaxation (nonradiative decay), whereas the dash-dotted arrows indicate sensitization processes.121