White luminescent emissions from HfO₂ and HfO₂:Al³⁺ layers deposited by ultrasonic spray pyrolysis technique

Polycrystalline HfO₂ and HfO₂:Al³⁺ coatings were synthesized by the spray pyrolysis technique. The photoluminescence and cathodoluminescence characteristics of the coatings were studied as a function of the synthesis parameters; the temperature of deposition and the dopant content (Al³⁺ions). A blue, bluish-white and warm white emission was found in the coatings, depending on the substrate temperature, doping concentration and excitation wavelength. The photoluminescence emission was enhanced with the increment of the deposition temperature and a quenching effect was also observed with the dopant concentration. The CIE chromatic coordinates: (0.3067, 0.3462), (0.3091, 0.3502) and (0.3073, 0.3498), were close to the ideal white emission. CCT values for some of the coatings make them potentially useful in white lighting systems. The structural characterization was also carried out by X-ray diffraction, SEM, HRTEM and EDS elemental composition.