Upconversion emission of LiNdP4O12 and KNdP4O12 crystals

► Bright upconversion emission in Li(K)NdP4O12 crystals in atmospheric pressure was governed by photon avalanche mechanism. ► The intense anti-Stokes white emission of Li(K)NdP4O12 crystals was observed in vacuum under 808 nm excitation. ► The mechanism of white emission has been discussed in term of Nd2+-charge transfer luminescence. ► Intensity of anti-Stokes white emission was strongly dependent of surrounding pressure and applied excitation power.