White Light–Generation Phosphor Ba[sub 2]Ca(BO[sub 3])[sub 2]:Ce[sup 3+], Mn[sup 2+] for Light-Emitting Diodes

Abstract

A pulsed bipolar electrodeposition procedure of palladium film onto polycrystalline gold surfaces from alkaline solution containing dianion Pd(CN)42−Pd(CN)42− complex was investigated. Several experimental parameters such as pulse amplitude, pulse frequencies, pH, K2Pd(CN)4K2Pd(CN)4 concentration, time of deposition, and electrode substrate, were evaluated and critically discussed. The palladium electrodeposition on the gold electrode substrates was performed using a multipulse of potentials. The optimized waveform should consist of oxidation potentials, E1=1.0VE1=1.0V vs saturated calomel electrode (SCE) and a reduction potential, E2=−1.0VE2=−1.0V vs SCE. The relevant pulse duration of t1=0.05st1=0.05s and t2=0.05st2=0.05s (repetition rate of 10Hz10Hz ) for 30 or 60s60s has to be chosen to give maximum efficiency of palladium electrodeposition. The deposited palladium film was characterized by using electrochemical and X-ray photoelectron spectroscopy (XPS) techniques. The probable mechanism of palladium electrodeposition involves in the first instance a strong and direct adsorption of Pd(CN)42−Pd(CN)42− complex on the gold surface at negative potentials, while during the subsequent anodic sweep, palladium oxide formation (PdOn)(PdOn) passes through the intermediate Pd(CN)2Pd(CN)2 product and the simultaneous formation of a stable Au(CN)2−Au(CN)2− complex. The reduction process of palladium oxide species to form Pd0Pd0 particles is simultaneously accompanied by the gold complex reduction process. The XPS analysis confirms the presence on the electrode surface of Pd0Pd0 , PdO, and PdO2PdO2 species, while the oxygen-containing species increase significantly with increasing the palladium surface concentration.