The OP538FC from TT Electronics is a Phototransistor with Collector Emitter Voltage (Breakdown) 30 V, Collector-Dark Current 225 nA, Collector Emitter Voltage(Saturation) 1.1 V, Emitter Collector Voltage(Breakdown) 5 V, On-State Collector Current 1.1 mA. More details for OP538FC can be seen below.