Verification of upconversion in ZBLAN:Ho3+ glass under photon-avalanche-type excitation at 980 nm

Following earlier predictions, we have attempted to excite a Ho3+:ZBLAN sample into the absorption-less region (980 nm) and obtained a distinct upconverted emission at ∼540 nm accompanied by two other longer wavelength bands. After performing additional lifetime measurements and simulation of the system kinetics, we provide a simple interpretation of the obtained results.