Understanding the photoluminescence behaviour in nano CaZrO3:Eu3+ pigments by Judd-Ofelt intensity parameters

Abstract

CaZrO3 ceramic pigment exhibits high chemical, thermal and structural stability. However, its application as a host for various luminophores/activators has not been clearly explored. In the present investigation, CaZrO3 doped with Eu3+, as a potential orange-red phosphor has been demonstrated. Ca1-xZrO3:Eux (x = 0.01–0.09) nanophosphor is prepared here through a low temperature, one pot solution combustion synthesis approach using glycine as the fuel. X-ray diffraction results show that all the samples are stabilized in orthorhombic crystal structure without any impurity phases. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high resolution TEM are carried out to determine the microstructure of the phosphor. The particles are found to be significantly agglomerated and in the nano-regime (∼40 nm). The observed excitation spectrum suggests that Ca1-xEuZrO3 can be efficiently excited using ultra-violet (UV), near-UV and UV blue (UVB), making it immediately relevant for current solid state lighting technologies. In fact with every ∼1 at% doping increase, the primary excitation line intensity increases by a factor of ∼1.5; this provides a simple parameter to enhance the UV excitability of the phosphor. The color coordinates are deduced using the Commission International De Eclairage (CIE) co-ordinates (x, y = 0.58, 0.40). The critical distance of energy transfer in this system is determined to be ∼10.7 Å, making multipole-multipole interactions as the plausible reason for concentration quenching beyond 7 mol.% Eu doping. The luminescence behaviour of the material is evaluated using Judd-Offelt (JO) intensity parameters. Judd-Ofelt (JO) intensity parameters (Ω2 and Ω4) are calculated for the sample Ca1-xZrO3:Eux (x = 0.01–0.09), in order to understand the local structure around the activator. Irrespective of the concentration of Eu3+, Ω2 is found to be greater than Ω4, indicating asymmetric environment around the activator. Furthermore, with increase in Eu3+, Ω2 increases suggesting an increase in covalency of Eu-O bonds with significant effect of host crystal field on Eu3+.