Quenching of tribo- and photoluminescence in a Tb$_2$(SO$_4$)$_3$ $\cdot$ 8H$_2$O + NaNO$_2$ crystalline mixture

It is found that the addition of NaNO$_2$ to Tb$_2$(SO$_4$)$_3$ $\cdot$ 8H$_2$O crystals quenches tribo- and photo-luminescence from the latter. In the case of triboluminescence, the glow of both Tb$^{3+^*}$ ions (solid component of triboluminescence) and N$_2^*$ molecules (gas component) is quenched. The NO$_2^-$ ion is known to be an efficient quencher of Tb$^{3+}$ ion luminescence by the mechanism of radiationless energy transfer in solutions. That quenching takes place when a crystalline quencher is in contact with a crystalline phosphor and also with a gaseous (molecular) phosphor seems to indicate that the excitation energy is transferred not only within individual crystals but also between contacting surfaces of the phosphor and quencher and at the gas-solid interface.