Upconversion fluorescence in Sm3+-doped zinc phosphate glassy matrix

The mechanism governing the upconversion fluorescence from the ⁴G_5/2 level of Sm³⁺ ion has been investigated in zinc phosphate glass matrices under infrared (1.06?µm) laser excitation. This visible emission is centred at 590?nm and corresponds to the ⁴G_5/2?→?⁶H_7/2 transition. The dependence of the integrated intensity on the excitation power confirms that this emission is due to the three-photon absorption process and is in agreement with the existing theory. The intensity of the upconversion fluorescence has a cubic dependence on the excitation power. An absolute upconversion efficiency of about 10^?7 was obtained for the sample doped with 0.5?wt% Sm³⁺ ions. A quantitative estimate of the number of photons leaving the sample was also determined.