White up-conversion luminescence of NaYF4:Yb3+,Pr3+,Er3+

• White up-conversion luminescence obtained from NaYF4:Yb3+,Pr3+,Er3+ (λexc: 976 nm).
• Up-conversion of Er3+ impurity observed due to efficient Yb3+–Er3+ energy transfer.
• The presence of Er3+ may boost the Pr3+ up-conversion luminescence.

Photon up-conversion which yields higher energy emission by stacking lower energy photons is possible only with specific rare earth ions. Despite this, it has several potential applications. NaYF4 with Yb3+,Er3+ co-doping has been recognized as one of the most feasible materials for efficient up-conversion luminescence. In this work, the up-conversion luminescence of the Pr3+–Er3+ combination was studied using sensitization by Yb3+. Emission was observed in the visible including blue, green, yellow, orange and red. These are due to the 3P0,1 → 3H4–6,3F2–4 and 1D2 → 3H4 (Pr3+) as well as 2H11/2,4S3/2,4F9/2 → 4I15/2 (Er3+) transitions. Concentration quenching of the Pr3+ luminescence was observed already with 1 mol-% due to many cross-relaxation processes. With naked eye, the up-conversion luminescence was seen as white light. The CIE chromaticity coordinates are close to those of the standard illuminant F4 which represents warm white.