The OP535A from TT Electronics is a Phototransistor with Collector Emitter Voltage (Breakdown) 15 V, Collector-Dark Current 100 nA, Collector Emitter Voltage(Saturation) 1.10 V, Emitter Collector Voltage(Breakdown) 2 V, On-State Collector Current 10.5 mA. More details for OP535A can be seen below.