Photoluminescence of rare-earth ion (Eu
3+
, Tm
3+
, and Er
3+
)-doped and co-doped ZnNb
2
O
6
for solar cells
Gao Sen-Pei
a),
b)
, Qian Yan-Nan
c)
, Wang Biao†
a),
b)
Excitation and emission spectra of undoped ZnNb
2
O
6
.