On the ultraviolet B emissions of CaLaB7O13:Gd3+ phosphor

UVB upconversion of LiYO2:Ho3+,Gd3+ for application in luminescence thermometry

“…As schematically illustrated by the simplified energy level diagrams of Gd 3+ and Ho 3+ ions shown in Fig. 3d, absorption of the first blue ∼445 nm photon can make energy populate the 5 F 1 / 5 G 6 states of Ho 3+ (ground state absorption, GSA), and then the energy nonradiatively relaxes to the lower-lying 5 F 3 and 5 F 4 / 5 S 2 states and blue (∼490) nm and green (∼551 nm) photoluminescence can be generated through the 5 F 3 → 5 I 8 and 5 F 4 / 5 S 2 → 5 I 8 transitions, [44][45][46] respectively. At the same time, from the relatively long-lived 5 F 3 and 5 F 4 / 5 S 2 excited states, the successive absorption of a second blue ∼445 nm photon will occupy the deep-UV excited states of Ho 3+ (excited state absorption, ESA), such as the 5 D j states at around 42 700 cm −1 and the 3 M 9 , 3 I 6 states at around 40 000 cm −1 .…”