The upconversion properties of Er^3＋-doped heavy metal oxyfluoride germanate glasses under 975 nm excitation have been investigated. The intense green （551 and 529 nm） and relatively weak red （657 nm） emissions corresponding to the transitions ^4S3/2→^4I15/2, ^2H11/2→^4 I15/2 and ^4F9/2 →^4I15/2, respectively, were simultaneously observed at room temperature. The content of PbF2 has an important influence on the upconversion luminescence emission. With increasing content of PbF2, the intensities of green （529 nm） and red （657 nm） emissions increase slightly, while the green emission （551 nm） increases markedly. These results suggest that PbF2 has an influence on the green （551 nm） emission more than on the green （529 nm） and red （657 nm） emissions.
Infrared-to-visible upconversion fluorescence of Er^3＋/Yb^3＋ co-doped lithium-strontium-lead-bismuth （LSPB） glasses for developing potential upconversion lasers has been studied under 975-nm excitation. Based on the results of energy transfer efficiency and upconversion spectra, the optimal Yb^3＋-Er^3＋ concentration ratio is found to be 5：1. Intense green and red emissions centered at 525, 546, and 657 nm, corresponding to the transitions ^2H11/2 → ^4I15/2, ^4S3/2→ ^4I15/2, and ^4 F9/2 →^4I15/2, respectively, were observed. The quadratic dependence of the 525-, 546-, and 657-nm emissions on excitation power indicates that a two-photon absorption process occurs under 975-nm excitation. The high-populated ^4I11/2 level is supposed to serve as the intermediate state responsible for the upconversion processes. The intense upconversion luminescence of Er^3＋/yb^3＋ co-doped LSPB glasses may be a potentially useful material for developing upconversion optical devices.
