Upconversion enhancement in Yb3+,Tm3+:BaY2F8 quasi-nanoparticles

► New quasi-nanocrystals (qNCs) Yb3+,Tm3+:BaY2F8 have been produced and analysed. ► A comparison with bulk crystal shows an enhancement of the upconversion efficiency. ► A possible explanation of this enhancement is given.