Up-conversion luminescence in the NdAl3(BO3)4 (NAB) microchip laser crystal

Abstract The infrared to visible luminescence of the Nd 3+ ion in the NdAl 3 (BO 3 ) 4 (NAB) laser crystal has been investigated in the 730–840 nm excitation spectral range. Green, yellow and red up-converted emission bands centred at about 535, 595 and 675 nm are observed under excitation within the 4 I 9/2  →  4 F 5/2 transition. All these emissions have been attributed to the transitions 4 G 7/2  →  4 I 9/2 (green), 4 G 7/2  →  4 I 11/2 (yellow) and 4 G 7/2  →  4 I 13/2 (red). From luminescence measurements and using a simple ratio equation model to fit the experimental data, it can be inferred that the 4 G 7/2 excited state is populated mainly via energy transfer up-conversion between Nd 3+ ions in the 4 F 3/2 metastable state.