Photon avalanche upconversion in Ho3+-doped gallium nano-garnets

• Synthesis of Ho3+ ions-doped Lu3Ga5O12 and Y3Ga5O12 nano-garnets is described.
• Intense green emission is observed by the naked eyes in both nano-garnets under 751 nm laser excitation.
• Photon avalanche process is responsible for the observed green emission at 545 nm.
• The threshold pump power density is found to be low for these nano-garnets.

Lu3Ga5O12 and Y3Ga5O12 nano-garnets doped with 1.0 mol% Ho3+ ions have been prepared by a citrate sol–gel method. Size distribution of the nano-garnets has been studied by dynamic light scattering technique. Intense green and weak red emissions have been observed in these nano-garnets under 751 nm excitation. The observed green upconverted emission is due to photon avalanche process, characterized by a threshold pump-power density and a time of establishment of 331 kW/cm2 and 33 ms for the Lu3Ga5O12 nano-garnets and 238 kW/cm2 and 18 ms for the Y3Ga5O12 nano-garnets, respectively. The results indicate that the nano-garnets are suitable for green upconversion photonic applications.