Temperature dependence of narrow-band UVB photoluminescence of silica-(Gd,Pr)PO 4 transparent glass-ceramic phosphors.

The effect of temperature on photoluminescence (PL) due to the 6 P j → 8 S 7/2 ( j = 5/2, 7/2) transitions of Gd 3+ ions was examined between 200 and 500 K for a sol-gel-derived silica-(Gd,Pr)PO 4 transparent glass-ceramic phosphor with negligible concentration quenching under excitation into the 5d-4f transition of Pr 3+ ions at 220 nm. The intensity of the narrow-band ultraviolet B (UVB) PL at ~313 nm associated with the 6 P 7/2 → 8 S 7/2 transition slightly increased between 200 and 300 K, but was decreased to ~86 and ~62 % of that at 300 K when temperature was raised to 400 and 500 K, respectively. The observed magnitude of the thermal quenching of the UVB PL intensity agreed well with that recorded in a prototype narrow-band UVB lamp consisting of another silica-(Gd,Pr)PO 4 transparent glass-ceramic window and a KrCl excimer lamp as a light source at 222 nm. The silica-(Gd,Pr)PO 4 transparent glass-ceramics was more resistant to thermal quenching of the narrow-band UVB PL than a conventional powder phosphor, probably because of the encapsulation of (Gd,Pr)PO 4 nanocrystals with low quenching centre concentrations in inert silica glass matrix.