Yb³⁺/Ho³⁺ doped Ba₃Y₂B₄O₁₂ phosphors: Upconversion luminescence and temperature sensing properties

Optical thermometry achieved by luminescent materials with good stability and high sensitivity has attracted much attention. In this article, Ba3Y2B4O12, a borate with good chemical stability and high laser threshold was chosen to be host material for preparing a series of Ba3Y2-x-yYbxHoyB4O12 (BYBO:xYb(3+)/yHo(3+); 0.01 <= x <= 0.35, 0.005 <= y <= 0.035) upconversion phosphors by a facile solid-state method. Under 980 nm excitation, phosphors show strong 551 nm green emission, weak 668 nm red emission, and 755 nm near-infrared emission, while bright greenlight can be observed by naked eye. When x = 0.15, y = 0.01, luminescent intensity obtains the maximum value. At higher doping concentration, the reduction of cell parameters caused by doping can accelerate the decrease of distance between dopants, so that the energy back transfer process is more likely to occur, weakening the green emission. The intensified non-radiative relaxation results in an increased red emission proportion at higher temperature. According to this rule, the temperature sensing properties based on the fluorescence intensity ratio I-668/I-551 and I-688/I-755 are studied. The maximum relative sensitivity (S-R) reaches 1.53 % K-1 at 478 K, which is higher than most of reported materials. It shows that BYBO:Yb3+/Ho3+ has application potential in temperature sensing.