Temperature dependent luminescence Cr3+-doped GdAl3(BO3)4 and YAl3(BO3)4

Chromium activated YAl3(BO3)4 (YAB) and GdAl3(BO3)4 (GAB) were synthesized and show efficient broad band near infrared emission under excitation in the UV, blue and orange spectral regions. Temperature dependent luminescence measurements for GAB:1%Cr3+ and YAB:1%Cr3+ reveal high quenching temperatures for the broad band Cr3+ emission, 620 K for YAB:Cr and 650 K for GAB:Cr. To gain insight in the luminescence the crystal field strength, Racah parameters, nephelauxetic effect and phonon coupling parameters have been investigated by using spectroscopic data. The crystal field splitting for Cr3+ is similar in the two borates (around 1670 cm−1). However, the calculated B Racah parameters indicate a higher global covalency in GAB. The electron phonon-coupling parameter (S) and the effective phonon energy (ħω) were determined to be 5.9 and 263 cm−1 for YAB and 5.4 and 309 cm−1 for GAB, respectively. The larger electron-phonon coupling strength in YAB:Cr is in agreement with the lower quenching temperature in comparison with GAB:Cr.