Near-infrared-to-visible upconverting luminescence of Er3+-doped CdSe nanocrystals grown by chemical bath

CdSe thin films were prepared by chemical bath and doped in situ with Er3+ ions. Three impurity levels were prepared by changing the relative volume of the salt solution containing Er3+ ions in the CdSe growing solution. Changes in the grain size (∼5.5-3.5 nm) and band gap energy (∼1.80-2.25 eV) were observed in the undoped and doped CdSe films, respectively. Photoluminescence studies displayed room temperature emission exhibiting NIR-to visible upconversion. The transition bands 4I13/2 → 4I15/2, 2I9/2 → 4I15/2 and 2F9/2 → 4F15/2 in the ∼700-850 nm region were investigated. Upconversion emissions were observed from the CdSeEr sample under light excitation (325 nm). The upconversion emission intensity ratio of these transitions is attributed to the variation of the local structure around Er3+ ions. These results confirm that visible upconversion emissions of Er3+ in the CdSeEr nanocrystals are mainly produced via two-photon excited-state absorption and energy transfer upconversion processes.