The influence of grain size and vanadium concentration on the spectroscopic properties of YAG:V3+,V5+ and YAG: V, Ln3+ (Ln3+ = Eu3+, Dy3+, Nd3+) nanocrystalline luminescent thermometers

The first demonstration of using V-based phosphor as a luminescent temperature sensor is presented. The luminescent properties of YAG:V3+, V5+ and YAG:V Ln3+ (Ln3+ = Eu3+, Nd3+ and Dy3+) nanocrystals were investigated in a wide range of temperature (-150 °C-300 °C). The influence of dopant concentration and size of the nanocrystals on the emission color output of the YAG:V3+, V5+ was analyzed. The provided analysis reveals that V3+ and V5+ are mainly localized in octahedral sites of Al3+ of core part of the nanocrystals and surface tetrahedral sites of Al3+, respectively. The emission spectra consists of two broad emission bands, attributed to the CT emission of V5+ (at 520 nm) and 3T2g → 3T1g electronic transition emission of V3+(at 820 nm). It was found that emission color output of the YAG:V3+, V5+ nanocrystals can be modulated either by the vanadium concentration or by the size of nanocrystals. Based on the V3+ to V5+ emission intensity ratio (LIR) in the temperature range from −150 °C to 300 °C self-reference thermometer was defined, which reveals 0.7%/°C of sensitivity at the physiological temperature and increases above 4% in 250-300 °C. However its usable temperature range was strongly restricted. It was showed that by the appropriate choice of lanthanide co-dopants, the temperature range in which high sensitivity can be modulated (0.4%/°C at 100 °C for YAG:V,Eu3+; 4%/°C at −150 °C for YAG:V,Dy3+; and 0.8%/°C at 300 °C for YAG:V,Nd3+).